# Reducing Squish on a Poulan Clamshell



## Chris-PA (Feb 14, 2015)

I have a nice running ported 42cc Poulan which was the subject of this thread: http://www.arboristsite.com/community/threads/yet-another-42cc-poulan-porting-thread.262612/ However, the squish clearance is large on these engines, and I wondered if I could reduce it. I believe it has been done before, mentioned in this thread: http://www.arboristsite.com/community/threads/wildthing-races-at-gtgs.140451/ but I did not know how. The problem is that the crankshaft must be repositioned in the cylinder:




I got to looking at this design. Unlike some other clamshells these engines are not machined other than the bore and the spark plug hole. The bearing pockets and bottom surface are as-cast (they are actually very nice castings):


Further, the bearings have a pretty thick rubber outer boot that surrounds them and forms the crank seal:




That means these engines can tolerate some slop in the location of the bearing pockets, and that with some sealant it really should not be hard to grind out those pockets - I can get that close by hand. I considered filing the cylinder lower surface with a hoof rasp (OK, a good flat file), but decided to turn it on a lathe instead. 

That presented a problem, because these engines are not turned at the factory and so they do not have a boss on the top for a tail support during turning:


There's just a spark plug hole. I wonder if they have a better plug location because of that?


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## treesmith (Feb 14, 2015)

How about extending the rod? Is that an option?


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## Chris-PA (Feb 14, 2015)

I decided to try printing a mandrel on the 3D printer, as I did not want to have to put much pressure up into the cylinder while it was on the lathe in the absence of a good boss for the tail support. This is what I came up with:


It was intended to lock into the bearing pockets for rotation. I decided to print it in ABS, which we had not done much of, since I figured I would need to turn the outer diameter (in the end I didn't have to), and the PET plastic is awfully soft. However, the ABS has a problem in that it shrinks and curls as it cools. I had to try a twice, and a few other experiments too. This took 9:15 to print, and I had to add a supporting structure. Here are some shots of the printing process:




Bottom view showing the support structure:


Here you can see that the outer wings curled - enough that the support structures pulled off the tapered lower portion:


I decided to try it anyway. After cutting away the support, here is how it fit:




I designed it so I could run a 7/16" aluminum hex rod through the center. I added a divot in the end for centering on the lathe. Oh, the shape of the end shaft was so that I would not have to use a lot of pressure on the jaws to keep it from slipping.




I epoxied the rod in with JB Quik


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## old-cat (Feb 14, 2015)

Cut or grind the flat mating surface of the cylinder where the pan fits. Take off the amount of squish reduction you want. Then you have to figure how to mount it in a lathe or mill to cut the bearing bore.


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## fordf150 (Feb 14, 2015)

cut your base to give the desired squish and chuck the cylinder in a mill and cut your bearing bore deeper into the cylinder by the same amount as you removed from squish.


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## Chris-PA (Feb 14, 2015)

I had a scrap jug from an earlier project and decided to try it first. Here is the lathe setup:


I need to grind out that wood block next time to better clear the plug boss. Here is the result:


I took measurements on each corner before I cut so I could see how even I got it. I need to spend a little more time indexing it for the real one, but it's pretty good.

That was pretty easy and the tool worked well. Now I had to deal with the bearing pockets, which I intended to cut with a sanding drum on a Dremel. But first I figured I'd need reference tool so I could see how I was doing. I measured the bearing pocket at a 36mm diameter, so I printed a tool at 37mm with thick side walls and turned it down:


I added some grooves so I could tell where the middle is. Here is how it fits in the factory castings:


So I tried it today, and it could not have been easier. Here is one side ground out (notice there is very little material to remove):

Here's how the reference tool fits (I think I'd go just a little further on the real thing:


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## fordf150 (Feb 14, 2015)

old-cat beat me to it but i have been thinking about this for awhile since nobody ever talks about doing these motors.


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## fordf150 (Feb 14, 2015)

i think at one point a boring bar was mentioned for cutting the bearing pockets deeper


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## Chris-PA (Feb 14, 2015)

I need to wait now until my new piston gets here - the intake will be too low if I cut the one I have. And of course I need to disassemble the engine and measure the squish with the new piston before cutting. So there will be a bit of a delay!


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## HuskStihl (Feb 14, 2015)

Chris-PA said:


> I decided to try printing a mandrel on the 3D printer, as I did not want to have to put much pressure up into the cylinder while it was on the lathe in the absence of a good boss for the tail support. This is what I came up with:
> View attachment 403561
> 
> It was intended to lock into the bearing pockets for rotation. I decided to print it in ABS, which we had not done much of, since I figured I would need to turn the outer diameter (in the end I didn't have to), and the PET plastic is awfully soft. However, the ABS has a problem in that it shrinks and curls as it cools. I had to try a twice, and a few other experiments too. This took 9:15 to print, and I had to add a supporting structure. Here are some shots of the printing process:
> ...


That's super-cool. How about a pop-up?


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## Chris-PA (Feb 14, 2015)

treesmith said:


> How about extending the rod? Is that an option?





old-cat said:


> Cut or grind the flat mating surface of the cylinder where the pan fits. Take off the amount of squish reduction you want. Then you have to figure how to mount it in a lathe or mill to cut the bearing bore.





fordf150 said:


> cut your base to give the desired squish and chuck the cylinder in a mill and cut your bearing bore deeper into the cylinder by the same amount as you removed from squish.





fordf150 said:


> i think at one point a boring bar was mentioned for cutting the bearing pockets deeper



I too have spent many hours thinking about how to do this, but I think it will turn out to be much easier than all of that. Truthfully, I think I could do it with a flat file and a sanding drum and a bit of careful measurement.


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## Chris-PA (Feb 14, 2015)

HuskStihl said:


> That's super-cool. How about a pop-up?


After Treemonkey's latest thread I almost decided to make a tool to cut the squish band and eliminate the small step there. However, there is not much meat on the casting or clearance for the counterweights, and I decided I didn't feel like pushing it.


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## RedneckChainsawRepair (Feb 14, 2015)

3000fps has done something like this a few years ago to tighten up his poulan clamshell. Just using good ole redneck ways.


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## Chris-PA (Feb 14, 2015)

JeremiahJohnson said:


> 3000fps has done something like this a few years ago to tighten up his poulan clamshell. Just using good ole redneck ways.


Yeah, as I said I have no doubt a file, a sanding drum and some careful measurements would do it. But it's Marbruary and things get dull you know?


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## RedneckChainsawRepair (Feb 14, 2015)

Chris-PA said:


> Yeah, as I said I have no doubt a file, a sanding drum and some careful measurements would do it. But it's Marbruary and things get dull you know?



I take it you didnt read the 6 page thread on the redneck way elsewhere. What file are you talking about?


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## Chris-PA (Feb 14, 2015)

JeremiahJohnson said:


> I take it you didnt read the 6 page thread on the redneck way elsewhere. What file are you talking about?


You lost me - was there a link I missed?


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## RedneckChainsawRepair (Feb 14, 2015)

Chris-PA said:


> You lost me - was there a link I missed?



Yep big time . But this place isnt friendly to other sites with info not here.  So no link you have to use google. 

Love the 3D stuff by the way.


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## Chris-PA (Feb 14, 2015)

JeremiahJohnson said:


> Yep big time . But this place isnt friendly to other sites with info not here.  So no link you have to use google.
> 
> Love the 3D stuff by the way.


Oh, ok - Depending on which site it is I'll see if I can find it. If it's on the other than I won't.


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## drf255 (Feb 15, 2015)

Great job Chris. 

Very interested in how it works out. 

I got a ton of 4047 alloy here. If you want a small dome welded on that you can turn down, just say the word.


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## Chris-PA (Feb 15, 2015)

Well the piston should arrive tomorrow and I'd like to disassemble the saw so I could get moving on this project. But not in an unheated barn at 10deg and blowing (assuming it actually gets that warm).


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## Moparmyway (Feb 15, 2015)

Great idea with the 3D printer !
When you drop the jug, do you think the counterweights will have enough clearance so they wont hit the casting by where the cylinder begins ?
How would you measure that clearance ?
The only way I could imagine would be clay or putty, then slice and measure


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## Chris-PA (Feb 15, 2015)

Moparmyway said:


> Great idea with the 3D printer !
> When you drop the jug, do you think the counterweights will have enough clearance so they wont hit the casting by where the cylinder begins ?
> How would you measure that clearance ?
> The only way I could imagine would be clay or putty, then slice and measure


Yes, that was one of my concerns. However, since I have the cutway engine in the first picture I can see in there pretty well. Just eyeballing it I'd say I've got around 0.070" until it hits, so I should be OK with the amounts I'm going to be cutting here.


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## Moparmyway (Feb 15, 2015)

Chris-PA said:


> Yes, that was one of my concerns. However, since I have the cutway engine in the first picture I can see in there pretty well. Just eyeballing it I'd say I've got around 0.070" until it hits, so I should be OK with the amounts I'm going to be cutting here.


You dont miss much .............. great ideas and another well put together thread !


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## HuskStihl (Feb 15, 2015)

Chris could probably end world hunger and eradicate disease if he didn't spend so much time on cheap clamshells.


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## Chris-PA (Feb 15, 2015)

Moparmyway said:


> You dont miss much .............. great ideas and another well put together thread !


Thanks - you've got me looking at that gap now on the cut way engine. That whole bottom cap is perfectly symmetrical to the crankshaft weights all the way around, and there is case volume there I'd like to get rid of!



HuskStihl said:


> Chris could probably end world hunger and eradicate disease if he didn't spend so much time on cheap clamshells.


Thank you, but you're the one with skills in that area and those are far more important than anything that can be done playing with little engines!


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## Wagnerwerks (Feb 15, 2015)

I have got to get a 3d printer.


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## RedneckChainsawRepair (Feb 15, 2015)

Chris-PA said:


> Well the piston should arrive tomorrow and I'd like to disassemble the saw so I could get moving on this project. But not in an unheated barn at 10deg and blowing (assuming it actually gets that warm).



-10F this morning and 0F as I type. Drifted shut right now. need to hook plow up later. Enjoy and good talking to ya.


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## Moparmyway (Feb 15, 2015)

Chris-PA said:


> Thanks - you've got me looking at that gap now on the cut way engine. That whole bottom cap is perfectly symmetrical to the crankshaft weights all the way around, and there is case volume there I'd like to get rid of!



If it was easy to grind/sand for proper bearing clearance on the block, then make an adapter for the cap and spin her up on the lathe - take off some material, re-shape the bearing bore, case volume reduced !!


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## Chris-PA (Feb 15, 2015)

Moparmyway said:


> If it was easy to grind/sand for proper bearing clearance on the block, then make an adapter for the cap and spin her up on the lathe - take off some material, re-shape the bearing bore, case volume reduced !!


Yeah, but all the cool guys are using epoxy these days, and I don't think that lowly Poulans should be neglected! Actually, dropping the cap as you suggest would only reduce that clearance in the center. However, if I print up a spacer and epoxy it into the cap I can reduce the gap all the way around. I just finished taking measurements and I'll try to print it tomorrow. Then I just have to JB Weld them into the cap.


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## Chris-PA (Feb 16, 2015)

I looked at the bottom cap for the clamshell, and realized that there were more differences between the earlier and later caps than I thought. I've always preferred the later caps as they added a groove on the ends to help seal to the cylinder. however, they also changed the shape of the part a bit:



For the purpose of reducing case volume I decided the earlier cap would work better. I drew up a filler - there was 1.5mm clearance to the counterweights, and I kept 0.5mm clearance:


I will glue them in tonight, but here is how they fit:



The material is PETG, which is pretty soft, so hopefully if there is a collision it will not be catastrophic.


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## Moparmyway (Feb 16, 2015)




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## Paragon Builder (Feb 16, 2015)

Pardon my ignorance... Why do you want to reduce case volume? This is pretty cool!!!


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## jackjcc (Feb 16, 2015)

Paragon Builder said:


> Pardon my ignorance... Why do you want to reduce case volume? This is pretty cool!!!


Boost transfer velocity. If there is no idle space than all movement of the engine results in fuel/air mix being forced into the transfer and into the combustion chamber, or drawing it into the bottom end from the carb.


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## Chris-PA (Feb 16, 2015)

Paragon Builder said:


> Pardon my ignorance... Why do you want to reduce case volume? This is pretty cool!!!


It's been a topic of discussion for a while - it's the purpose of "crank stuffers" - basically plastic fillers that round out the crankshaft counterweights. The idea is that with a 2-stroke the engine must draw air into the case, and then squeeze it up the transfers into the cylinder. But of course air is compressible. If you imagine some ridiculously large volume (like say the case was as big as your room, with the inlet on the other side from the piston). It's still sealed, so if the piston goes up it will eventually draw a volume of air equal to the cylinder into the big case, but it may take a while. If the piston is moving very fast then it will just reduce the pressure locally a bit and not much air will be drawn in.

So if you can reduce the volume of the case relative to the displacement, you can improve the pumping efficiency and move more air into the case, as well as increase the pressure pushing it up the transfers.


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## Paragon Builder (Feb 16, 2015)

Ahh, I get it! Like trying to pull a vacuum, pressurize a space. The less volume the quicker either can happen. Correct?


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## Paragon Builder (Feb 16, 2015)

Thanks! While I was writing you explained my thoughts with more elegant words. [emoji106]


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## HuskStihl (Feb 16, 2015)

But if you reduce the volume too much you can lose power


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## Paragon Builder (Feb 16, 2015)

HuskStihl said:


> But if you reduce the volume too much you can lose power


Because too small means not enough room to "store" the charge?


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## Hedgerow (Feb 16, 2015)

Why wouldn't you just use a piston with a taller deck height?
Maybe I missed a post?


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## Hedgerow (Feb 16, 2015)

HuskStihl said:


> But if you reduce the volume too much you can lose power


More case volume = more HP to an extent..


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## Paragon Builder (Feb 16, 2015)

Hedgerow said:


> More case volume = more HP to an extent..


?????
Ok, that sounds like you might want to increase from stock?
How do you figure out that fine balance?


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## Red Amor (Feb 16, 2015)

yall very clever fellers ;O) good thread thanks


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## Chris-PA (Feb 16, 2015)

HuskStihl said:


> But if you reduce the volume too much you can lose power


I have read that, but I'm not sure what the mechanism for it would be. The only thing I can think of would be in the mechanical resistance as the case build pressure - but you can control that by reducing the case compression angle. Hey, it's an experiment!



Hedgerow said:


> Why wouldn't you just use a piston with a taller deck height?
> Maybe I missed a post?


Well, I haven't got one! Actually, this has mostly been playing around to stave off cabin fever, but as it turns out it's been surprisingly easy. Enough so that playing around with fitting other pistons seems like it would be a hassle.


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## Chris-PA (Feb 16, 2015)

Oh, I found a way to measure the volume of the fillers I made - they reduce the case volume by 3cc. I wish I could measure the total case volume easily.


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## Hedgerow (Feb 16, 2015)

Paragon Builder said:


> ?????
> Ok, that sounds like you might want to increase from stock?
> How do you figure out that fine balance?


There is a case volume/displacement ratio, but that one is above my pay grade... Successful platforms have been built on both extremes though..
Chris' platform/case volume, is rather tight already, so it will be interesting to see what the stuffers do to the useful operating rpms..


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## Paragon Builder (Feb 16, 2015)

Ok great! I'm absorbing as much of this as I can.


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## drf255 (Feb 16, 2015)

Great Job Chris.


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## Paragon Builder (Feb 16, 2015)

drf255 said:


> Great Job Chris.


Love your avatar!


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## LegDeLimber (Feb 16, 2015)

Any chance of carving out a step in the flat face of the pan, where the radius meets the corner?
I'm thinking of a having a tab on the end of that insert and the tab being captive between the pan and the cylinder base, when they're assembled.
Of course that would mean a redrawn & printed insert.
If the insert rolls up while the motor's at full throttle, I'm kinda envisioning a 
"How to straiten your Clam-Crank" project.

Not wishing bad weather on anyone, but these cabin fever, Marbruary projects 
that come out of it, are some interesting/entertaining reading.


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## mp5n (Feb 16, 2015)

Chris,

What was the squish before you started? On another note I want your calculator! Is it a 11C or 15C?


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## drf255 (Feb 16, 2015)




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## kz1000 (Feb 16, 2015)

Why not just buy a real saw?


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## Hedgerow (Feb 16, 2015)

At this point, it's not about the destination...
It's about the journey..


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## Chris-PA (Feb 16, 2015)

LegDeLimber said:


> Any chance of carving out a step in the flat face of the pan, where the radius meets the corner?
> I'm thinking of a having a tab on the end of that insert and the tab being captive between the pan and the cylinder base, when they're assembled.
> Of course that would mean a redrawn & printed insert.
> If the insert rolls up while the motor's at full throttle, I'm kinda envisioning a
> ...


Good thinking - I tried to do something similar, in that there is a 1mm radius on the edge of the cap, and the same on the edge of the cylinder. I originally drew it with a bump there to try to lock in to that seam, but the printer prints with a 0.35mm string and it just wasn't giving good enough detail on a geometry that small. Then too, with the PETG material and the thin wall that piece is not stiff enough to lock in well anyway. So I'm just going to JB Weld it in - there is no force on it other than vibration. 



mp5n said:


> Chris,
> 
> What was the squish before you started? On another note I want your calculator! Is it a 11C or 15C?


It was 0.040". That seems to be pretty typical for this series of Poulan. 

It's an 11C and you can't have it! I've had it since college - I was staggered at what they go for on eBay. I have an app for it on my iPhone.



kz1000 said:


> Why not just buy a real saw?


Seriously? Why does it bother you? It's a cheap 20 year old saw that will already embarrass many more expensive saws, what's not real about it? 



Hedgerow said:


> At this point, it's not about the destination...
> It's about the journey..


Exactly, thank you for getting it!


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## Hedgerow (Feb 16, 2015)

I am sure I have seen them somewhere else before, but what did the transfers look like on that model?


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## LegDeLimber (Feb 16, 2015)

Need the fluid and gas engineers to weigh in with some jargon here!
Tight as you're swinging the crankweights to the insert, at 9 thou or so,
There's going to be a pretty surprising amount of drag against the inserts, imposed by craknweights.
I expect there a strong pressure wave just infront and between the weights and insert
and Then a negative one, just behind them, as things are spinning.
lots of dynamic load changing will be happening, IF and I say IF i'm thinking correctly.


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## Chris-PA (Feb 16, 2015)

Hedgerow said:


> I am sure I have seen them somewhere else before, but what did the transfers look like on that model?



This is an earlier one I did, but transfers are the same:


They did change the shape in later years. 



LegDeLimber said:


> Need the fluid and gas engineers to weigh in with some jargon here!
> Tight as you're swinging the crankweights to the insert, at 9 thou or so,
> There's going to be a pretty surprising amount of drag against the inserts, imposed by craknweights.
> I expect there a strong pressure wave just infront and between the weights and insert
> ...



There should be 0.018" to 0.020" clearance to the filler. 

I think there should be a pressure wave in front of the big, flat counterweights of this saw, which was the subject of this thread: http://www.arboristsite.com/community/threads/clamshells-transfer-shape.232407/page-2#post-5194065

It is a secondary reason I'm filling in that gap at the bottom of the engine, to help build pressure before the transfers open. Of course I cannot get rid of the big slot in the middle where the rod goes - though I have tried to figure out what I could do there too!


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## tree monkey (Feb 16, 2015)

Hedgerow said:


> There is a case volume/displacement ratio, but that one is above my pay grade... ..



1.2 to 1


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## Chris-PA (Feb 16, 2015)

Well, I'm a total idiot - I blew it! See the nice bevel on the counterweights - and the total lack of a bevel on the boss on the other end:



I was test fitting prior to gluing them in, and of course it isn't going to work - not without bevelling the boss. A matching bevel won't quite get into the pin hole, and it's pretty wide, so I'm considering it. I have no way to know how much it will weaken the crank or how much margin it has. Then again it's an old cheap engine.


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## LegDeLimber (Feb 16, 2015)

What, maybe 3/4 of the way, or better, to the pin?
Just remember to cut it in the lathe and don't file or sand it axially.
Don't want the really badly oriented stress lines that would create.


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## Hedgerow (Feb 16, 2015)

Chris-PA said:


> This is an earlier one I did, but transfers are the same:
> View attachment 404279
> 
> They did change the shape in later years.
> ...


The squish improvement will help your cause, but you'll have to deal with your transfers .. They're simple, but not efficient... Of course that may not be the objective here.. But you should raise them the same amount you dropped the jug.


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## Chris-PA (Feb 16, 2015)

LegDeLimber said:


> Just remember to cut it in the lathe and don't file or sand it axially.
> Don't want the really badly oriented stress lines that would create.


I have to measure again more carefully, but something like that. The OD at the crank pin boss is smaller than at the counterweights. One benefit of the wide weights is that the pin boss is considerably wider than on other cranks 

I'll take your advice on not grinding - I had not thought about that aspect.



Hedgerow said:


> The squish improvement will help your cause, but you'll have to deal with your transfers .. They're simple, but not efficient... Of course that may not be the objective here.. But you should raise them the same amount you dropped the jug.


Yeah, I know, and I've not really been able to do an acceptable job on raising transfers before, but I'm going to have to deal with that. I'll have to come up with something. I have a bunch of scrap cylinders to practice on.


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## Hedgerow (Feb 16, 2015)

tree monkey said:


> 1.2 to 1


And there you have it...


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## Chris-PA (Feb 16, 2015)

tree monkey said:


> 1.2 to 1


Wow, that's tight! Considering it has to be at least 1:1 that gives you only 20% of the displacement for case volume.


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## angelo c (Feb 16, 2015)

Just loggin in to follow along with my "buddy from up the hill"


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## tree monkey (Feb 16, 2015)

120% of displacement


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## Hedgerow (Feb 16, 2015)

Chris-PA said:


> Wow, that's tight! Considering it has to be at least 1:1 that gives you only 20% of the displacement for case volume.


But you'll have to ask him what the desired outcome of that ratio is...



Different strokes for different folks...


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## Hedgerow (Feb 16, 2015)

tree monkey said:


> 120% of displacement


Is that for max HP? Rpm's be damned??
And why am I thinking that's not all that tight??


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## Hedgerow (Feb 16, 2015)

Stephen C. said:


> transfer rate. Higher ratios will move more fuel/air


In most cases, yes..
Unless you lose your velocity..


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## dirt_19 (Feb 16, 2015)

looking forward to reading any further progress  . Subscribed


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## Chris-PA (Feb 16, 2015)

tree monkey said:


> 120% of displacement


I'm confused as to what that means - the case should be 120% of displacement or 20%? 

This is 42cc and the piston has a simple flat lower edge. That edge sweeps 42cc in the case. There is volume under the piston that is considerably more than 20% of the swept volume, so just the volume under the piston crown at TDC to the lower edge of the skirt at BDC is way more than 120%

On this saw the volume of the crank/counterweight cavity plus the transfers is something like 2.5 X the displacement. If I add the swept volume plus the volume under the piston it's around 4 X the 42cc. Then again it has enormously thick flywheel weights. 

My little cap fillers will reduce the total case volume by less than 2%. It would require crank stuffers to make any significant difference. But I'll probably try it anyway.


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## LegDeLimber (Feb 16, 2015)

Actually you should be able to remove the stock in about any fashion that's handy.
Just remember to polish things out to remove any valleys or grooves that run axially 
or even on a helix.
Keep everything running radially for the final finish work.
Believe I'd take a good close look a the holes in the outer walls of the crank weights too.
Just in case there are any voids, pitting or manufacturing dings from ham-handed workers.


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## Hedgerow (Feb 17, 2015)

The more


Stephen C. said:


> huh? If the case compression is increased how can it decrease velocity? Oh never mind...[/QU


If the time/area of the upper transfers is increased and you have less degrees of crank case compression from dropping your intake down, you could end up with a net loss in velocity..
Though I doubt that will be a problem with this saw in question..


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## Moparmyway (Feb 17, 2015)

Chris-PA said:


> It would require crank stuffers to make any significant difference.


   

Print them up and JB them in.
It has to be lighter than making a full circle crank out of pure JB


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## kz1000 (Feb 17, 2015)

kz1000 said:


> Why not just buy a real saw?


That was an attempt at humor that failed Chris, I'm always in the back ground watching what you achieve out of these critters. Sorry


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## Chris-PA (Feb 17, 2015)

Moparmyway said:


> Print them up and JB them in.
> It has to be lighter than making a full circle crank out of pure JB


I have been going over and over that! I think you would need to turn the OD of the crank counterweight/pin boss to allow a retaining ring, or a notch for a wire, or something. The stuffer would likely have to be in 4 parts as I'm not sure there is enough clearance to go around the pin boss, and eve if there were it would be really thin. At first I thought it was doable, but now I don't think it would be so easy.

Besides, I still think the wide crank weights were intentional and they were trying for some sort of pressure wave effect at the transfers - they make other cranks that are much narrower. The whole saw design was effected by how wide the crank/engine is. Anyway, I'm still exploring that and don't want to defeat it by filling out the crank weights.



kz1000 said:


> That was an attempt at humor that failed Chris, I'm always in the back ground watching what you achieve out of these critters. Sorry


And I darn well should have known that given your comment history. Sorry for being too touchy!


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## HuskStihl (Feb 17, 2015)

Touchy bastard. So according to TM a 42cc (it's funny to even type a number that small in front of "cc") saw should have a crankcase volume between 42 and 50cc for maximum power. Smaller volume will increase compression and speed they the transfers, but at some point, it will blow the unburned charge straight out the exhaust port


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## weimedog (Feb 17, 2015)

First, I really appreciate the fact you are willing to push boundaries to make things happen...
Second, I think you with an obvious engineering background should continue to follow your instincts as you have despite what you may see in the commentary.
Three...an interesting read relative to case volume & intake timing:
(Note some applies and some doesn't but what it does do is help with defining directions to explore.)
http://www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdf


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## weimedog (Feb 17, 2015)

HuskStihl said:


> Touchy bastard. So according to TM a 42cc (it's funny to even type a number that small in front of "cc") saw should have a crankcase volume between 42 and 50cc for maximum power. Smaller volume will increase compression and speed they the transfers, but at some point, it will blow the unburned charge straight out the exhaust port



All fun aside, How do you calculate or measure that volume? If the piston volume and transfer volume is included, that's a very small area. Are you just considering the volume of the case itself? Or the entire system when the piston is at BDC? Seems to me there are practical limits based on crank, case, transfer port, and piston design. And in those less than optimal designs, intake size & timing along with Transfer size & timing can help mitigate issues. Would rather see this as a baseline all things perfect and then push the other numbers as a discussion when they can't be. I guess a random number doesn't compute for me. A number in context with the other "numbers" defining a system does.

( Now if I had a "Solid Modeling Based Cad System... that calculation might be a bit easier.. Even that would be "plus or minus" some based on the accuracy of the models and the way that system does Booleans & calculates volume)


----------



## Grande Dog (Feb 17, 2015)

Howdy,
Good read. I like the stuffers. Depending on how well it scavenges, you might want to put a rougher surface on them. Chris, it looks like you don't have any lack of tools. If you have the tools to do it, a cam ground crank pin will do the trick for adjusting squish on a clamshell.
Regards
Gregg


----------



## Chris-PA (Feb 17, 2015)

HuskStihl said:


> it's funny to even type a number that small in front of "cc"


Think of it as 4200mm3!



weimedog said:


> an interesting read relative to case volume & intake timing:
> (Note some applies and some doesn't but what it does do is help with defining directions to explore.)
> http://www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdf


Thanks for that - it's going to take some digesting!



weimedog said:


> How do you calculate or measure that volume? If the piston volume and transfer volume is included, that's a very small area. Are you just considering the volume of the case itself? Or the entire system when the piston is at BDC?


This is what confuses me - what is included and what is not, and is it at TDC or BDC (max or min)? The only thing that makes sense to me is that it excludes the volume of the cylinder. 



Grande Dog said:


> I like the stuffers. Depending on how well it scavenges, you might want to put a rougher surface on them. Chris, it looks like you don't have any lack of tools. If you have the tools to do it, a cam ground crank pin will do the trick for adjusting squish on a clamshell.


Thanks, but other than the printer I actually don't have much to work with other than the usual drill presses, Dremels and such. I can use the shop at work, but that mostly just gets me an old lathe. All the CNC mills and lathes are set up for production. So taking apart the crank and cam grinding the pin is out of my capability. 

I'll have to give the surface finish some thought - it had not occurred to me.


----------



## Chris-PA (Feb 17, 2015)

I was working from home today and the temperature got up high enough to work in the barn, so I took a break and took the engine out and apart. I also tried my hand once again at grinding the transfer outlets. I cut down a cut off wheel and that did seem to work OK, but still a bit hard to control. 

The new piston should arrive tomorrow, but first I have to try turning the crankshaft. After that I can attach the piston and do a test fit to measure the squish and port timing, and then cut the cylinder appropriately.


----------



## Hedgerow (Feb 17, 2015)

Chris-PA said:


> This is what confuses me - what is included and what is not, and is it at TDC or BDC (max or min)? The only thing that makes sense to me is that it excludes the volume of the cylinder.


Should consist of what's under the piston and in the crank case and transfer ports when piston is at BDC...


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## cobey (Feb 17, 2015)

Hedgerow said:


> Should consist of what's under the piston and in the crank case and transfer ports when piston is at BDC...


 dang thats what i was thinking.... I might be understanding this stuff


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## mdavlee (Feb 17, 2015)

Chris-PA said:


> I was working from home today and the temperature got up high enough to work in the barn, so I took a break and took the engine out and apart. I also tried my hand once again at grinding the transfer outlets. I cut down a cut off wheel and that did seem to work OK, but still a bit hard to control.
> 
> The new piston should arrive tomorrow, but first I have to try turning the crankshaft. After that I can attach the piston and do a test fit to measure the squish and port timing, and then cut the cylinder appropriately.


Have you thought of 2 small grooves a little higher on the transfers to start flowing a little earlier than the whole thing to see if it gains rpms? Just thinking out of the box here with the open port set up.


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## Chris-PA (Feb 17, 2015)

Hedgerow said:


> Should consist of what's under the piston and in the crank case and transfer ports when piston is at BDC...


OK, using that definition and the measurements I took last night, it looks like this engine starts off around 2:1. My filler blocks will reduce the case volume by 3.6% - not much.


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## Chris-PA (Feb 17, 2015)

mdavlee said:


> Have you thought of 2 small grooves a little higher on the transfers to start flowing a little earlier than the whole thing to see if it gains rpms? Just thinking out of the box here with the open port set up.


That would probably be easier to do.


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## tree monkey (Feb 17, 2015)

1.2 to 1 is supposed to be optimal, for what ever that's worth. I don't think it can be achieved.
full circle cranks will reduce volume more then anything.



it's painted to seal the epoxy


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## heyduke (Feb 17, 2015)

just a question. i'm stoked with what you're trying to do, but are you working at the wrong end? might it be easier to cut the top off the cylinder and machine a new head with the desired squish/compression ratio? it would make it easier to mod the transfers too. my understanding was that the mission was to reduce the .040" squish. we all get a little crazy at this time of year.


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## Hedgerow (Feb 17, 2015)

tree monkey said:


> 1.2 to 1 is supposed to be optimal, for what ever that's worth. I don't think it can be achieved.
> full circle cranks will reduce volume more then anything.
> View attachment 404592
> 
> ...


It just wouldn't be a genuine pic from Augusta without a mtn dew can in it...
Has it ever got "real" cold up there yet?


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## Homelite410 (Feb 17, 2015)

I want to do a jb weld popup n see how long it lasts in a compression/fire environment!


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## tree monkey (Feb 17, 2015)

Hedgerow said:


> It just wouldn't be a genuine pic from Augusta without a mtn dew can in it...
> Has it ever got "real" cold up there yet?



yes it's cold and windy


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## Homelite410 (Feb 17, 2015)

I give it a tank!


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## Hedgerow (Feb 17, 2015)

tree monkey said:


> yes it's cold and windy


I wish someone woulda got a pic of Alan and I trying to start that stupid frost bit splitter with the recoil and electric start at the same time...
I can only imagine what it's like now...
We ***** when it gets below 10 here..


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## tree monkey (Feb 17, 2015)

-35 below with wind chill


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## cobey (Feb 17, 2015)

tree monkey said:


> -35 below with wind chill


 wow!...... im not gonna complain about our 7 deg. tonight


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## Hedgerow (Feb 18, 2015)

tree monkey said:


> -35 below with wind chill


Yuk...


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## LegDeLimber (Feb 18, 2015)

Homelite410 said:


> I want to do a jb weld popup n see how long it lasts in a compression/fire environment!


I'm curious as to what results some of this type of aluminum brazing rod give.
durafix dot com
=


heyduke said:


> just a question. i'm stoked with what you're trying to do, but are you working at the wrong end? might it be easier to cut the top off the cylinder and machine a new head with the desired squish/compression ratio? it would make it easier to mod the transfers too. my understanding was that the mission was to reduce the .040" squish. we all get a little crazy at this time of year.


That had me thinking about this Wild Thing parts saw, For about 5 mins. 
And then I looked at the prices for copper shim stock.
Hmmm, maybe I could weave a loop from some of that 22g dollar store speaker wire.

Picked this one up a couple yeras ago, off C'list. Yeah another victim of running with the brake on.
Surprisingly the crank seal wasn't melted, Saw actually cranked pretty easily.
It's all there, just got that melted problem.


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## Moparmyway (Feb 18, 2015)

Chris-PA said:


> I have been going over and over that! I think you would need to turn the OD of the crank counterweight/pin boss to allow a retaining ring, or a notch for a wire, or something. The stuffer would likely have to be in 4 parts as I'm not sure there is enough clearance to go around the pin boss, and eve if there were it would be really thin. At first I thought it was doable, but now I don't think it would be so easy.
> 
> Besides, I still think the wide crank weights were intentional and they were trying for some sort of pressure wave effect at the transfers - they make other cranks that are much narrower. The whole saw design was effected by how wide the crank/engine is. Anyway, I'm still exploring that and don't want to defeat it by filling out the crank weights.





tree monkey said:


> full circle cranks will reduce volume more then anything.
> View attachment 404592
> 
> 
> it's painted to seal the epoxy



Maybe not so complex ........... ???


----------



## heyduke (Feb 18, 2015)

LegDeLimber said:


> I'm curious as to what results some of this type of aluminum brazing rod give.
> durafix dot com
> =
> 
> ...




yeah, i wish i had $5 for every time someone brought a saw to the shop with the chain "jammed." just gently explain the function of the chain brake and send them on their way. i've also encountered a totalled poulan where the hombre had re-installed the clutch cover with the chain break on. didn't know his own strength.


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## Chris-PA (Feb 18, 2015)

heyduke said:


> just a question. i'm stoked with what you're trying to do, but are you working at the wrong end? might it be easier to cut the top off the cylinder and machine a new head with the desired squish/compression ratio? it would make it easier to mod the transfers too. my understanding was that the mission was to reduce the .040" squish. we all get a little crazy at this time of year.


Well, setting aside the case stuffer thing, so far dropping the cylinder has been pretty easy. It's hard to imagine cutting off the top would be easier - and since this is a clamshell there are no through bolts, so I don't know how you'd reattach it.

Of course I have not done the real cylinder yet and put it back together, so we'll see!



LegDeLimber said:


> Yeah another victim of running with the brake on.
> Surprisingly the crank seal wasn't melted, Saw actually cranked pretty easily.
> It's all there, just got that melted problem.


I have to point out this is the ONLY Poulan or Husqvarna plastic cased saw with an inboard clutch. It's a change they made at the time they changed the 42cc model over to strato - now it has the Stihl melted case disease too. They didn't make that mistake twice though, and the PP5020 has an outboard clutch and metal cover.


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## Chris-PA (Feb 18, 2015)

Moparmyway said:


> Maybe not so complex ........... ???


I think I remember that there is more to those crank stuffers than just epoxy, but I have not found the thread. 10,000rpm would put a lot of force on them!


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## LegDeLimber (Feb 18, 2015)

I was wondering about the stuffers and that rpm too. Was also thinking of some sort of "rebar" scheme.
Can't recall if there has been a detailed description of how they're done.
The act of setting a mold ring around the weights is pretty much a case of make sure it's centered/true and will clear everything as the crank turns, yada yada...
But I cant recall if the mold wall is also a strap that gets left in place after filling in the large open areas that the crank weights don't occupy.


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## heyduke (Feb 18, 2015)

Chris-PA said:


> Well, setting aside the case stuffer thing, so far dropping the cylinder has been pretty easy. It's hard to imagine cutting off the top would be easier - and since this is a clamshell there are no through bolts, so I don't know how you'd reattach it.
> 
> Of course I have not done the real cylinder yet and put it back together, so we'll see!.



yes, you're right. i was only brain storming although "brain" might be an exaggeration... i wasn't thinking about how the pan bolts up. a head gasket would be a challenge too.


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## LegDeLimber (Feb 18, 2015)

Looking at Chris-pa cutaway pics, sort of leaves you thinking of a ring of 
number 8 or 10 diameter screws to hold the head on one of these.
Would be a pretty slick task to align your drilling pattern to precisely hit the that cylinder wall with every hole.


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## Chris-PA (Feb 18, 2015)

So I beveled the crank around the pin boss. It wasn't too bad, but I had to go very slow - it's a sloppy old lathe and I got a bit of chatter on one side. I probably had the cutter too high too. I matched the angle of the cutter to the bevel on the counterweights, and cut the pin boss until I heard it begin to touch the weights. 

I also had some trouble epoxying the fillers in the cap, as the epoxy was so thick that the one filler did not seat well enough, so I had to do some sanding. I think I have it clearanced pretty well now, but may have to do a little more. 

Here are some shots of the setup and the crank:









With this new piston the squish is now 0.043", so I know what I need to cut off the cylinder.


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## LegDeLimber (Feb 18, 2015)

Change your tool bit to just cut with a smaller area 
Set it like My childish looking sketch.
Keep the nose radius vs tool size proportional to what I scratched out
and You'll see a big improvement in the cutting action! 

When you have a broad face cutting like you did there,
it will be really bad to cause chatter.

Edit: you'll need to rotate the compound and feed by hand,
in order to keep the tool at the angle I show.
Unless you have the odd/semi-rare lathe with with an angle drive
ability on the compound.


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## Homelite410 (Feb 18, 2015)

I would have set the compound to desired angle and used a .060" radius cutter. Just my .02


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## LegDeLimber (Feb 18, 2015)

One other thought: If you have *any* of those chatter lines on the crankpin area,
You should file and smooth them off.
I cant tell from the pics if there are any.


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## Mastermind (Feb 18, 2015)

Really cool thread Chris. 

I raised the crank in a Wild thing once......just to see if I could. I milled the base, and used a boring bar to fly cut the bearing pockets. It was pretty simple really.


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## fordf150 (Feb 18, 2015)

Haha my dumb+ss remembered something. I knew it was a boring bar to cut the pockets


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## Mastermind (Feb 18, 2015)

It worked well. I was able to spin a .030" popup on the piston. 

It had an air leak here........but you get the idea.


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## Chris-PA (Feb 19, 2015)

LegDeLimber said:


> Change your tool bit to just cut with a smaller area
> Set it like My childish looking sketch.
> Keep the nose radius vs tool size proportional to what I scratched out
> and You'll see a big improvement in the cutting action!
> ...





Homelite410 said:


> I would have set the compound to desired angle and used a .060" radius cutter. Just my .02


Thanks for the tips guys. I'll freely admit I don't know my ass from my elbow when it comes to cutters and lathes. I do normally use the corner of the cutter, but on this lathe I don't know how to adjust the compound angle and I didn't want to change the setup. I'll talk to the machinist today and ask him how to do it though - it was after hours when I turned it and he wasn't around.


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## Homelite410 (Feb 19, 2015)

Get us a picture of the carriage without a tool post on it I bet we can help you out!


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## LegDeLimber (Feb 19, 2015)

Give him a few months on a universal mill ("Bridgeport") and 
we'll have him able to freehand that 45deg with the saddle and cross slide!!

I'll say it again: I MISS being in a nice little machine/fab shop.


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## old guy (Feb 19, 2015)

Mastermind said:


> It worked well. I was able to spin a .030" popup on the piston.
> 
> It had an air leak here........but you get the idea.



Is that chuckleing sound as the saw decelerates an indication of an air leak? any saws I heard do that always cut very well and I thought it was a good state of tune. I fear my ignorance is showing.

John


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## Moparmyway (Feb 19, 2015)

Mastermind said:


> I was able to spin a .030" popup on the piston.



BLASPHEMY !!!!! 
YOU did WHAT ??????? 
My world now stands crushed !!!!!


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## Chris-PA (Feb 19, 2015)

OK, I know how to adjust the angle on the lathe now!


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## Mastermind (Feb 19, 2015)

old guy said:


> Is that chuckleing sound as the saw decelerates an indication of an air leak? any saws I heard do that always cut very well and I thought it was a good state of tune. I fear my ignorance is showing.
> 
> John



That is a classic air leak sound. It had a crack in the JB Weld external transfers. 



Moparmyway said:


> BLASPHEMY !!!!!
> YOU did WHAT ???????
> My world now stands crushed !!!!!



Yeah.....when I was a newbie I used popups. I'm not a newbie anymore......


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## Chris-PA (Feb 19, 2015)

Mastermind said:


> Yeah.....when I was a newbie I used popups. I'm not a newbie anymore......


So you've reached that age where pop ups just aren't happening any more?


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## Mastermind (Feb 19, 2015)

Chris-PA said:


> So you've reached that age where pop ups just aren't happening any more?



I'm not saying that popups are a bad idea. They work just fine in many applications. I was pushed into cutting the squish bands by guys that wanted me to build them a saw without a popup. Some people just do not want a custom made piston in their engine. 

After doing hundreds of saws with a cut squish band.......using a popup piston just seems like going backward rather than forward.


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## Mastermind (Feb 19, 2015)

Chris-PA said:


> So you've reached that age where pop ups just aren't happening any more?



Oh wait........you were making a funny.


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## Chris-PA (Feb 19, 2015)

OK, I hope to cut the cylinder down this evening, and I'm trying to decide how small to set the squish. My initial thought was to shoot for around 0.018" But then I got to thinking about how the crank is essentially mounted in rubber bushings, and I wonder if it moves at all? The rubber coating is pretty thin and clamped down well, so I'm hoping it doesn't move too much. 

I guess if I go too far I can always take a little off the piston.


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## Mastermind (Feb 19, 2015)

Chris, I would take off .040......then set clearance by cutting a popup.


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## Chris-PA (Feb 19, 2015)

Mastermind said:


> Chris, I would take off .040......then set clearance by cutting a popup.


Yeah, I've been toying with that. It gives me more to grind out the the bearing pockets, but that doesn't seem to be a big deal.


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## Mastermind (Feb 19, 2015)

As large as that lathe is you probably could use it to cut the bearing pockets. Mounting the jug on a back plate wouldn't be as tough as you might think.


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## Chris-PA (Feb 19, 2015)

Mastermind said:


> As large as that lathe is you probably could use it to cut the bearing pockets. Mounting the jug on a back plate wouldn't be as tough as you might think.


Nah, I'm going to grind them out by hand with a Dremel like I did on the practice cylinder. It was easy to do using the sizing gauge I made.

I guess I won't be cutting the cylinder today - got a call that someone's been stealing my firewood, so I'm going home to find out what's up with that. Frozen green white oak isn't going to help them much.


----------



## Chris-PA (Feb 19, 2015)

Well, it looks like it was a scrounger taking some punky, fractured stuff I had decided to leave next to the road. Doesn't look like he went back into the woods after my real stacks - what my wife thought was a trail to those stacks was just a deer path. 

Now I wish I had stayed at work and cut that cylinder. Oh well, It's going down to -7 tonight so I got a head start on getting the stoves cranking. Hopefully the guy that took that wood needs it to keep warm tonight.


----------



## Mastermind (Feb 19, 2015)

It's suppose to be -6 here tonight. Thanks a lot PA.


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## Mastermind (Feb 19, 2015)

Stephen C. said:


> it was -7 several hours ago when I was running around doing errands. It is now -17 and the wind is blowing, had -26 last night, supposed to be colder tonight.
> I can't bring myself to go to the barn to mess with saws in these temps.



I don't blame you. 

We've got a good heater in the shop.......and the shop is small. Well insulated too.


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## Mastermind (Feb 20, 2015)

12 degrees warmer than it was at daybreak.


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## Mastermind (Feb 20, 2015)

We have lots of people with frozen water right now. I was able to get 16" minimum when I ran my line from the water meter. A lot of people have less soil than that. 

We had to blast for the septic tank.


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## Chris-PA (Feb 20, 2015)

Well, I cut 0.040" off the cylinder, and I'm happy with how it came out:


Tomorrow I'll try grinding out the bearing pockets.

I also cut both the new piston and the old one:




There's nothing wrong with the old piston, but there is a notch cut in the skirt and I think the intake duration will be too long now. After I get the bearing pockets done I can try mounting the pistons and measuring squish and timing.


----------



## Chris-PA (Feb 20, 2015)

We have a scotchbrite belt at work, and I used it to smooth the crankshaft where I cut it, and the counterweights:


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## Mastermind (Feb 20, 2015)

Chris did you get a benchmark to see if you will be getting good gains from this compression increase. I know you will.....but think the difference may be huge.


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## Chris-PA (Feb 20, 2015)

Mastermind said:


> Chris did you get a benchmark to see if you will be getting good gains from this compression increase. I know you will.....but think the difference may be huge.


I had run the saw a fair amount, but I don't have any consistent wood to use as a before/after benchmark. And I will have changed several things at once by the time it's back together. However, I did run it against my stock engined saw (in some very hard hickory ), so I can redo that comparison I suppose.


----------



## Mastermind (Feb 20, 2015)

I do believe the first one had a better chain. Is that right?


----------



## Flattop Burns (Feb 20, 2015)

Grande Dog said:


> Howdy,
> Good read. I like the stuffers. Depending on how well it scavenges, you might want to put a rougher surface on them. Chris, it looks like you don't have any lack of tools. If you have the tools to do it, a cam ground crank pin will do the trick for adjusting squish on a clamshell.
> Regards
> Gregg




Was it just me but did that just seem like you and your buddies were camping and Lyle Alzado or Kent Tekulve walked out of the woods and sat down next to the fire said something and then walked off into the night?


----------



## Chris-PA (Feb 20, 2015)

Mastermind said:


> I do believe the first one had a better chain. Is that right?


That was a variable - the first was Carlton lo pro, and this one had Oregon 91PX. Generally I find them to be very close. I was disappointed that the ported saw was not faster - it felt faster and was more willing to rev, but it didn't show in the times. Chain could have been a factor.


----------



## Mastermind (Feb 20, 2015)

Timed cuts really mean very little to me. There is too much emphasis put on the cut times has the only indicator of which saw is "better".

Like you said, the ported saw felt better.....that's what really matters. I've yet to meet a tree with a stopwatch.


----------



## Mastermind (Feb 20, 2015)

This thread is the most interesting thing I've seen on this site in awhile. 

Thanks Chris.


----------



## Flattop Burns (Feb 20, 2015)

It's true. Me and a first cousin are building his 4218 to run better he got for $119 with a case and sharpening kit. Somehow I got interested in winding up the little creature a bit being as it was a tough saw to begin. All we did so far was put two holes in the deflector that were turboconed from the inside and put spacers on the deflector retainer stud to space it a bit farther than it was with just the (now deleted) screen alone. It was an improvement but just the first step.


----------



## Mastermind (Feb 20, 2015)

These saws were the first ones that I started doing "strange" things on. External transfers, carb swaps, etc.....

If you kill one you've not broke the bank........you can find another and keep playing.


----------



## drf255 (Feb 21, 2015)

Really great job Chris. 

I'm interested in the compression increase as well. 

I learned the hard way on my MS250 project that a little dome goes a long way on these guys. You remember the thread.


----------



## Duke Thieroff (Feb 21, 2015)

Instead of cutting the jug, why not the engine pan?


----------



## Chris-PA (Feb 21, 2015)

Duke Thieroff said:


> Instead of cutting the jug, why not the engine pan?


I suppose you could grind out the bearing pockets in the cylinder, and cut the edge of the pan down, but then the split between the cylinder & pan would not be in the center any more, and the bearing hole would not be completely round. The distortion would be small though, so it could probably be filled with sealant. I'll have to think about how to fixture the pan so it could be cut down.


----------



## Chris-PA (Feb 21, 2015)

After hauling firewood and other chores getting ready for the snow, I got to spend a bit of time in the barn on this project. It was about 22deg. I got the bearing pockets ground out - it took a little while to take off 0.040", but it wasn't hard. I had to go slow and keep checking. Here is what I used:


I used the gauge I made, along with a measurement from that raised ridge that holds the bearings in. I also used the bearings as the seam between the cap and the cylinder is impressed into the rubber. Here's how the gauge fit:


And here's the finished cylinder:



I ended up with 0.021" squish, which is close enough given all the things I had to cut. 

Timing with the new piston is (duration/deg from TDC):

E = 150/105
I = 158/79
T = 106/127
Which gives a BD of 22 and a case compression angle of 48. I'm not going to raise the transfers at this point as I don't want to risk damaging the cylinder, and I'm not convinced it needs it.

I think I'd like a little lower case compression angle though, so I'm considering trimming 0.050" off the piston skirt to get an intake duration of 166, and a case compression of 44.

I hope to get the engine together tomorrow.


----------



## Moparmyway (Feb 22, 2015)

Great idea on trying it first, before the transferrs get any treatment from the grinder (or cutoff wheel) !
Looking forward to seeing this run !!


----------



## auskip07 (Feb 22, 2015)

Chris looking at the end of the transfers the 90* shelf at the top of the transfer. Could you gain any air speed/flow by inserting a peice to smooth out that bend? Its essentially a dead corner


----------



## Chris-PA (Feb 22, 2015)

auskip07 said:


> Chris looking at the end of the transfers the 90* shelf at the top of the transfer. Could you gain any air speed/flow by inserting a peice to smooth out that bend? Its essentially a dead corner


From what I have read an outlet angle of 90deg is desirable (although I have not thoroughly investigated why). Surely the air in the back corner of the upper transfer will be dead air, which effectively makes it curved anyway. A more sophisticated casting would have a transfer runner that loops further back from the bore and comes in from a larger radius, but this is an inexpensive design.


----------



## Chris-PA (Feb 22, 2015)

It runs! After I got done moving snow I cut the lower edge of the piston up by 0.050" to increase the intake duration, and put it back together. It fit properly in spite of all the cutting:




I had to sand down the lower edge of the intake/air box seal because that part of the cylinder is now lower, and I could not get the bolts started. I little more work with the sanding drum:



Here is the finished port timing:



I didn't have much to cut that was out of the snow other than a small old chunk of pine - I cut that but of course it didn't tell me much! There are a lot of variables that have changed, including the port timing and the new ring which will need to seat. Subjectively it feels pretty snappy and seems to want to rev, but I'll have to reserve judgment until I can get it in some wood. Hopefully I can post s video soon.


----------



## barneyrb (Feb 22, 2015)

After all the 3d printing and high tech equipment you have access to you wound up using a dremel tool?


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## Chris-PA (Feb 22, 2015)

barneyrb said:


> After all the 3d printing and high tech equipment you have access to you wound up using a dremel tool?


The 3D printer is about the only "high tech" equipment I do have access to. Other than that it an old worn out lathe driven by a leather belt, some drill presses and belt sanders. The CNC stuff is all set up for production work and I don't know how to use it anyway (although I have been considering learning to program one). And a Dremel.


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## auskip07 (Feb 22, 2015)

barneyrb said:


> After all the 3d printing and high tech equipment you have access to you wound up using a dremel tool?



macgyver would be proud of chris


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## Chris-PA (Feb 22, 2015)

auskip07 said:


> macgyver would be proud of chris


Lol, thanks. In fact the 3D printed stuff was just playing around. This could be done with a flat file and a dremel, and the old bearing as a reference. Or at least if you just take off the difference to get the right squish, rather than doing the pop up for which you'd need a lathe.


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## Wood Doctor (Feb 22, 2015)

I think I need to send Chris a non-running Poulan 42/18 in a carton. It has a new piston and rings, has hardly been run, and still will not start. Maybe he can save it or tell me how I can save it.


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## auskip07 (Feb 22, 2015)

Wood Doctor said:


> I think I need to send Chris a non-running Poulan 42/18 in a carton. It has a new piston and rings, has hardly been run, and still will not start. Maybe he can save it or tell me how I can save it.



They are easy to work on i brought back to life my Poulan Pro 260


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## Wood Doctor (Feb 22, 2015)

auskip07 said:


> They are easy to work on i brought back to life my Poulan Pro 260


OK, I'm all ears. After installing a new piston and rings (saw looked like it was straight-gassed), it still seems to have insufficient compression to start, even with a good spark and carb settings as recommended. Saw has very few hours on it and looks brand new. My Stihl dealer told me to stop wasting my time on junk. What's next for me to try?


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## Chris-PA (Feb 22, 2015)

Wood Doctor said:


> I think I need to send Chris a non-running Poulan 42/18 in a carton. It has a new piston and rings, has hardly been run, and still will not start. Maybe he can save it or tell me how I can save it.


These saws are so straightforward you should be able to get it running. Check the flywheel for a sheared key/tab, and fuel line which often fail. 

Also use the purge bulb to diagnose the lines/carb - it should pull fuel with very few bubbles. If you get air then it is either the lines or a leaking check valve in the carb. 

Fuel line routing can get mixed up too - the small fuel line should go to the carb nipple near the end with the cover with the single center screw. The line from the nipple nearest the mixture screws goes to the purge bulb inlet, and the purge bulb outlet goes back to the tank, ususlly through a larger line.


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## Wood Doctor (Feb 22, 2015)

Chris-PA said:


> These saws are so straightforward you should be able to get it running. Check the flywheel for a sheared key/tab, and fuel line which often fail.
> 
> Also use the purge bulb to diagnose the lines/carb - it should pull fuel with very few bubbles. If you get air then it is either the lines or a leaking check valve in the carb.
> 
> Fuel line routing can get mixed up too - the small fuel line should go to the carb nipple near the end with the cover with the single center screw. The line from the nipple nearest the mixture screws goes to the urge bulb inlet, and the purge bulb outlet goes back to the tank, ususlly through a larger line.


OK, Chris, I'll double check all of that. But, I think that's what I already did in November. Compression still seems nil compared to any Stihl that I own, and that's usually the bottom line. I was very careful when rebuilding the top end and saw no difference in rope pull resistance after completing it. Not much is more depressing than that. I'll report back what I find and show you a Pic of the piston before I started.


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## redfin (Feb 22, 2015)

Thanks for posting this Chris. I'm eager to see the results.


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## VinceGU05 (Feb 22, 2015)

i recently done up a MS390. being a clamshell. i went the easiest option to boost the comp. 





tried this but fouled.. so got a stock piston and with the aid of Plasticine, got am imprint from the combustion chamber along with the plug in! 




ended up with something similar to this . and ended up with 185 psi. all standard port timing as nothing else was changed.


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## Moparmyway (Feb 23, 2015)

Chris-PA said:


> The 3D printer is about the only "high tech" equipment I do have access to. Other than that it an old worn out lathe driven by a leather belt, some drill presses and belt sanders. The CNC stuff is all set up for production work and I don't know how to use it anyway (although I have been considering learning to program one). And a Dremel.


Handicapped or blessed ......... even a combination of them, you did a fantastic job. What I am really looking forward to is the fact that you could easily cut another cap and swap out the stuffed one to see what difference those 3D inventions make. I love the timing charts you do !!

Great job !!


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## Chris-PA (Feb 23, 2015)

Wood Doctor said:


> OK, Chris, I'll double check all of that. But, I think that's what I already did in November. Compression still seems nil compared to any Stihl that I own, and that's usually the bottom line. I was very careful when rebuilding the top end and saw no difference in rope pull resistance after completing it. Not much is more depressing than that. I'll report back what I find and show you a Pic of the piston before I started.


Do you know what the squish is? These engines are easy to pull over stock, so maybe it is not a sign of a problem with the piston/cylinder.


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## angelo c (Feb 23, 2015)

Wood Doctor said:


> OK, I'm all ears. After installing a new piston and rings (saw looked like it was straight-gassed), it still seems to have insufficient compression to start, even with a good spark and carb settings as recommended. Saw has very few hours on it and looks brand new. My Stihl dealer told me to stop wasting my time on junk. What's next for me to try?



Doc, 
will it fire if you force feed a few drops down the exhaust or intake ? should still pop and fire somewhat uncontrolled.


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## auskip07 (Feb 23, 2015)

angelo c said:


> Doc,
> will it fire if you force feed a few drops down the exhaust or intake ? should still pop and fire somewhat uncontrolled.



Not if he isnt getting spark


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## Chris-PA (Feb 23, 2015)

Sitting here at work wishing I was home and the ground & wood were not covered with snow so I could try that saw out for real.


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## angelo c (Feb 23, 2015)

auskip07 said:


> Not if he isnt getting spark


Absotively , my assumption was he confirmed spark and was concerned for compression. If it won't fire with known spark well then it can only be "timing" or compression.


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## angelo c (Feb 23, 2015)

Chris-PA said:


> Sitting here at work wishing I was home and the ground & wood were not covered with snow so I could try that saw out for real.


Soon we'll be complaining about the heat and ticks.... !!!


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## Chris-PA (Feb 23, 2015)

angelo c said:


> Soon we'll be complaining about the heat and ticks.... !!!


And mud.


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## angelo c (Feb 23, 2015)

Chris-PA said:


> Sitting here at work wishing I was home and the ground & wood were not covered with snow so I could try that saw out for real.



I hear ya...


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## Chris-PA (Feb 23, 2015)

Stephen C. said:


> heat ticks and mud all sound wonderful this weather is really getting me down...........
> View attachment 406418


What is that that "-" symbol in front of the number 18? That's a bad thing, right?



angelo c said:


> View attachment 406419
> 
> 
> I hear ya...


Hey, I see some wood sticking out there - enough to run a saw in for a few minutes anyway!


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## angelo c (Feb 23, 2015)

Chris-PA said:


> What is that that "-" symbol in front of the number 18? That's a bad thing, right?
> 
> 
> Hey, I see some wood sticking out there - enough to run a saw in for a few minutes anyway!


Sure thing...come and join me. Bring some saws. I got a few we can run too.
Id say we'd last a good 15-20 minutes at least....shop is in the basement. ...plenty heat there.


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## Wood Doctor (Feb 23, 2015)

angelo c said:


> Doc,
> will it fire if you force feed a few drops down the exhaust or intake ? should still pop and fire somewhat uncontrolled.


Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.

Is it worth removing the cylinder again? How could there be practically no compression at all? I've never seen anything like this.


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## auskip07 (Feb 23, 2015)

Wood Doctor said:


> Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.
> 
> Is it worth removing the cylinder again? How could there be practically no compression at all? I've never seen anything like this.



I would say kep trying. There has to be something you missed.


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## angelo c (Feb 24, 2015)

Wood Doctor said:


> Model is 18/42. Saw measures 25 psi compression, which is nothing. All cylinder mounting bolts are tight. Original was straight gassed. I installed a new piston and rings. Spark is good. Engine hardly has any hours on it.
> 
> Is it worth removing the cylinder again? How could there be practically no compression at all? I've never seen anything like this.



Doc, 
Its got to be leaking somewhere. Spark plug, case fittings, seals ect. can you add some pressure and hunt down the leak.
maybe start another thread and keep Chris's focused on hotrodding a clam. lets get yers runnin then have Chris turn up the volume !!!


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## drf255 (Feb 24, 2015)

VinceGU05 said:


> i recently done up a MS390. being a clamshell. i went the easiest option to boost the comp.
> 
> 
> 
> ...


Great job. Did you use 4047 filler rod?

It seems like whatever size dome your minds eye predicts for these should be halved. I'm surprised you got only 185 psi with that dome. The chamber space much be rather large on a 390. 

Did you relieve the piston under the dome at all? What weight difference did you come up with?


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## Wood Doctor (Feb 24, 2015)

angelo c said:


> Doc,
> It's got to be leaking somewhere. Spark plug, case fittings, seals ect. can you add some pressure and hunt down the leak. Maybe start another thread and keep Chris's focused on hotrodding a clam. lets get yers runnin then have Chris turn up the volume !!!


OK, I'll back out. I took it apart again and found the problem. A chunk of the lower right rear (carb side) corner of the cylinder broke off. It must have had a hairline crack in it that I didn't see when I installed the new piston and ring. Funny thing also, the piston ring was broken, even though the saw never started and ran after I installed it. Anyway, at least we now know why there was no compression.

Are you guys sure that these saws are built well enough and tough enough to hot rod them? I have to wonder after seeing this.


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## Chris-PA (Feb 24, 2015)

Wood Doctor said:


> Are you guys sure that these saws are built well enough and tough enough to hot rod them?


The castings are quite nice on these - remember, the only machining that gets done is the bore and the spark plug hole. The rest must be accurate enough to use without machining, so it can't be junk. I'm not sure what happened on yours, but I've never had one break - just the typical scoring and stuff.


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## auskip07 (Feb 24, 2015)

Stephen C. said:


> Oh yes. I think the guys had a wild thing build off a couple years ago. The ones that lost the competition were amazing. The winner was unbelievable in the power it put out. This is Masterminds saw. Seems to run pretty well even with the air leak.





Where is that thread? i would love to read it. Im sure i could get my hands on a wildthing for around 30 dollars


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## Chris-PA (Feb 24, 2015)

auskip07 said:


> Where is that thread? i would love to read it. Im sure i could get my hands on a wildthing for around 30 dollars


No doubt, but Wild Things have no A/V system. They did make plenty of equivalent saws with quite nice A/V, often sold as Craftsman or Poulan Pro. The Poulan Pro versions further have chromed cylinders - at least the ones prior to the later strato engines did.


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## auskip07 (Feb 24, 2015)

Chris-PA said:


> No doubt, but Wild Things have no A/V system. They did make plenty of equivalent saws with quite nice A/V, often sold as Craftsman or Poulan Pro. The Poulan Pro versions further have chromed cylinders - at least the ones prior to the later strato engines did.



It looks like the one i have is just a nicer version of the Wild thing, it has a chrome cylinder and AV system. So i guess ill just keep modifying mine


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## VinceGU05 (Feb 24, 2015)

drf255 said:


> Great job. Did you use 4047 filler rod?
> 
> It seems like whatever size dome your minds eye predicts for these should be halved. I'm surprised you got only 185 psi with that dome. The chamber space much be rather large on a 390.
> 
> Did you relieve the piston under the dome at all? What weight difference did you come up with?



yes i used 4047 rod on it. and the dome ended up 5mm bigger in diameter. and .5mm higher than that shot.. i should have taken a final pic.
yes its a pretty deep chamber! i didnt relieve the piston. weight added would be 5 to 10 grams max i think.


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## LegDeLimber (Feb 25, 2015)

VinceGU05 said:


> i recently done up a MS390. being a clamshell. i went the easiest option to boost the comp.
> 
> ended up with something similar to this . and ended up with 185 psi. all standard port timing as nothing else was changed.



I gotta ask. What's the story behind the line (crack?) across the top of the piston in pic 3?


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## LegDeLimber (Feb 25, 2015)

This project has me thinking of a couple of the Pre-strato, 46cc poulans sitting here that will need piston & ring(s), possibly a cylinder for a strait gassed one
(but that one will likely never get put back together - parts saw!)
So I looked at prices and see that the cyls are NLA on some sites and the pistons are hitting 
$28~ 39, depending on the site.


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## VinceGU05 (Feb 25, 2015)

LegDeLimber said:


> I gotta ask. What's the story behind the line (crack?) across the top of the piston in pic 3?



It's just a mark from when I cut the plasticine with a knife to see the cross section to check clearances from plug and chamber. 
A bit like using solder to measure the squish.


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## Chris-PA (Feb 25, 2015)

VinceGU05 said:


> It's just a mark from when I cut the plasticine with a knife to see the cross section to check clearances from plug and chamber.
> A bit like using solder to measure the squish.


I did consider having a buddy add some aluminum to the piston top so I could make bigger pop up, but in the end I decided not to risk the piston. This version of the Poulan cylinder has a decently small and well shaped combustion chamber (without having a boss cast into the top of the cylinder for turning, they were free to locate the spark plug there). 

Also, I re-calculated the volume of my case inserts - they reduce the case volume by 5%. It's still not much, but a bit more than I first thought. I wish I had taken today off so I could run it!


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## Chris-PA (Feb 28, 2015)

Well, I have a nasty head cold and sore throat, everything is coved with snow and I could not get the tractor back to the wood pile. But I trudged through anyway, and then I was out of storage space on my phone, but I got one poorly exposed video at least!



The thing actually ran really well, and I doubt the ring is seated yet. I'm pretty happy with it. This is frozen white oak, and I measure 3.5 to 4sec faster than my ported Earthquake in the same round (when it was not frozen):



Now I'm going to load the little stove in the living room and crank the heck out of it, and sit there and bake.


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## auskip07 (Feb 28, 2015)

very nice. Im assuming the earthquake is a lesser CC?


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## Chris-PA (Feb 28, 2015)

auskip07 said:


> very nice. Im assuming the earthquake is a lesser CC?


Thanks! The Earthquake is 38cc, but it is also ported and has the base cut for better compression.


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## Chris-PA (Mar 15, 2015)

Well it's been a couple of weeks but the snow has finally melted enough that I could get to a wood pile, I'm mostly over the cold I had and it isn't pouring rain - which meant I could try out the saw a bit. In the mean time I got a new GB bar for it:



This bar is supposed to be 18" but is actually a full 19" from the case installed (19.5" with the chain), which is pushing it for a 42cc saw. The chain is 91VXL.

I don't like to waste wood cutting cookies so I noodled a few instead. I'm really pretty happy with this saw - it's got guts. This is noodling white oak with a knot, almost full bar:

It's working pretty hard but I think it's decent given the bar length.

Also, it illustrates how stupid the Piltz stuff is! This heavily modified 42cc saw can actually pull this bar with lo pro, but no way a smaller saw can handle a longer bar.


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## bikemike (Mar 15, 2015)

LegDeLimber said:


> This project has me thinking of a couple of the Pre-strato, 46cc poulans sitting here that will need piston & ring(s), possibly a cylinder for a strait gassed one
> (but that one will likely never get put back together - parts saw!)
> So I looked at prices and see that the cyls are NLA on some sites and the pistons are hitting
> $28~ 39, depending on the site.


I was able to get a ring for my 46cc from jacks small engine. Shipping cost 3 times the price of the part


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## bikemike (Mar 15, 2015)

Chris-PA said:


> Well, I have a nasty head cold and sore throat, everything is coved with snow and I could not get the tractor back to the wood pile. But I trudged through anyway, and then I was out of storage space on my phone, but I got one poorly exposed video at least!
> 
> 
> 
> ...



Runs real nice


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## Paragon Builder (Mar 15, 2015)

Chris-PA said:


> Well it's been a couple of weeks but the snow has finally melted enough that I could get to a wood pile, I'm mostly over the cold I had and it isn't pouring rain - which meant I could try out the saw a bit. In the mean time I got a new GB bar for it:
> View attachment 412135
> 
> 
> ...



I was noodling today myself. Mostly with my 61, and a little with my 55. That saw is strong for 42cc!! Nice job, Chris!!!


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## bikemike (Mar 15, 2015)

bikemike said:


> Runs real nice


Il have to get a vid of my poulan posted now that i got the new ring in it


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## bikemike (Mar 15, 2015)

Poulan pro 46cc


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## Chris-PA (Mar 15, 2015)

bikemike said:


> Poulan pro 46cc



Ha ha - very cool!


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## bikemike (Mar 15, 2015)

Chris-PA said:


> Ha ha - very cool!


Its not bad for a old saw. Its got many hours on it and still runs like a champ. I did put the husky 136 clutch cover on it instead of the tooless crap


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## old guy (Mar 15, 2015)

That clutch cover did catch my eye, I don't know if my stock 2900 will keep up wit dat saw.

John


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## bikemike (Mar 15, 2015)

old guy said:


> That clutch cover did catch my eye, I don't know if my stock 2900 will keep up wit dat saw.
> 
> John


What size is the 2900 in displacement?


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## Chris-PA (Mar 15, 2015)

bikemike said:


> What size is the 2900 in displacement?


It's the same 46cc saw as yours.


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## bikemike (Mar 15, 2015)

Chris-PA said:


> Well it's been a couple of weeks but the snow has finally melted enough that I could get to a wood pile, I'm mostly over the cold I had and it isn't pouring rain - which meant I could try out the saw a bit. In the mean time I got a new GB bar for it:
> View attachment 412135
> 
> 
> ...





Chris-PA said:


> It's the same 46cc saw as yours.


If your looking to pipe your saw dont do what i did with the pocket bike pipe. Get one for a go ped they are very nice


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## Chris-PA (Mar 15, 2015)

Here was my 46cc:


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## bikemike (Mar 15, 2015)

I likke all the vids coming up


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## bikemike (Mar 15, 2015)

This here is 10 times the pipe than what i have it is for a go ped and will let a saw screem with a broad power band especially for big or hard wood


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## LegDeLimber (Mar 15, 2015)

I keep thinking about something like that ,tucked in around my leaf blower.
Got room for a nice glasspack end can. and it would have to be close to the moded mufler on it now, noisewise. Actually would preffer to get the DBs a bit lower and carrying a couple extra pounds on a backpack wouldn't be that big of a deal to me.

The power band would have to run from no higher than 5000-ish to around 7500~7800 rpm.
ah but seems I've so many more ideas than dollars nowdays.


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## old guy (Mar 15, 2015)

bikemike said:


> What size is the 2900 in displacement?


46cc

John


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## Chris-PA (Mar 29, 2015)

Another video - I wanted to try it out with a more typical bar length rather than the oversized GB bar. This is a bar from a McCulloch that is supposed to be 18", but is actually 17". I got it on a used saw and had to modify it so it would oil, otherwise it was similar to an A041 mount bar. It's 60DL rather than the 62DL typical on Poulans. The chain is WodlandPro (Carlton) lo pro.



I'm really happy with the way this thing runs. I put the GB bar back on it after a while and have decided that it pulls the longer bar just fine, and oils it well, so I'm leaving that on. I have other lighter saws to use the shorter bars on.


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## Moparmyway (Mar 29, 2015)

NICE !!
She handles changes in load very well !!!


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## drf255 (Mar 30, 2015)

Chris, that saw runs great!

Good luck with it.


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## old-cat (Mar 30, 2015)

http://www.ebay.com/itm/GO-PED-HIGH...167?pt=LH_DefaultDomain_0&hash=item3a93579abf


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## Chris-PA (Mar 30, 2015)

old-cat said:


> http://www.ebay.com/itm/GO-PED-HIGH...167?pt=LH_DefaultDomain_0&hash=item3a93579abf


Neat, but this is a real working saw - it's the one made out of pieces of various saws that doesn't have a case or a place on the shelf. It sits on the floor of the shop, and consequently it's the one that gets picked up most often. Besides, the port timing isn't set up for a pipe, and if I wanted to do that I'd have to go and read all those 2-stroke tuning books that don't apply to saws!

It sure is cool looking though!


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## old-cat (Mar 30, 2015)

Chris-PA said:


> Neat, but this is a real working saw - it's the one made out of pieces of various saws that doesn't have a case or a place on the shelf. It sits on the floor of the shop, and consequently it's the one that gets picked up most often. Besides, the port timing isn't set up for a pipe, and if I wanted to do that I'd have to go and read all those 2-stroke tuning books that don't apply to saws!
> 
> It sure is cool looking though!


Perfect for a little top handle saw!!! HaHaHa


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## Chris-PA (Jun 29, 2015)

So how long will the 3D printed inserts last? Longer than I expected, but not forever:



Actually I figured they would fail immediately, and they held up for quite a few tanks. This evening I was noodling up some oak knots, and it ran great. I set it down and picked it up and restarted - it started, bogged, and a thick white cloud of smoke came out the muffler. It stank like heck too. I was pretty sure what it was!

It looks like one of the plastic parts pulled up, and then it cleaned off all the rest. The epoxy pulled off completely. The piston, cylinder and ring look ok but will need the junk cleaned off. Epoxy and PETG plastic aren't really appropriate materials for inside the crankcase of an internal combustion engines.

Now I have to decide what I'm going to do. The thing ran so nice I don't want to give up anything, but I doubt I will put it back the same way. I don't really think the volume reduction was that effective, but I do think the fillers helped direct the pressure wave off the front of the counter weights up the transfers. I have another idea about that I want to explore.


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## Paragon Builder (Jun 29, 2015)

I'm interested in your idea! But in the meantime maybe put it back together to see the difference those made??


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## Chris-PA (Jun 29, 2015)

Paragon Builder said:


> I'm interested in your idea! But in the meantime maybe put it back together to see the difference those made??


I should, but that may be more work than I want to do. I _really_ liked the way this saw ran. 

I'm not sure I'll do the other idea, as I was just considering that turning new inserts out of aluminum on the lathe would be pretty easy. Just turn an appropriate bevel onto a disk, then part it into a ring and cut it into two inserts. Probably epoxy would be ok holding aluminum to aluminum.


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## smokey7 (Jun 30, 2015)

The clamshells i did poulan 3314 and eager beaver. I made a new lower pan with a cmm machine and a program on the cnc. I moved up the bearing pockets up.050 and and welded a .020 popup. I dont know what the port timing, is just it now blows 227psi with .019. Squish now and runs a 18" bar no problem. I widened
exhuste 2mm per side with no transfer tining change. Just lightly trimmed. It now runs with 4816 and a pp5020. neck and neck with a hot 350. Someone know why that works so well? She now 4 strokes hard at 14800- 15200 which i barely could 10500 before.What u guys think. Both of these saws have almost 10-15 gal of mix at 40:1 with 93 premium no ethanol..


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## drf255 (Jun 30, 2015)

Wouldn't welding a popup piston just be easier Chris?

I'm intrigued by your work, for sure. It just stinks that it only lasted that long. 

I'd be glad to weld a piston up for ya, just say the word.


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## bikemike (Jun 30, 2015)

With a goodheavy mix these saws will run forever. when youreduced squish050 inch you may want to consider running up the ports 050 inch so you get your port timing back. but then again the smaller transfer opening may be why its running great by forcing the new fuel air mix to the top of the cylinder with less mixing of spent gasses


smokey7 said:


> The clamshells i did poulan 3314 and eager beaver. I made a new lower pan with a cmm machine and a program on the cnc. I moved up the bearing pockets up.050 and and welded a .020 popup. I dont know what the port timing, is just it now blows 227psi with .019. Squish now and runs a 18" bar no problem. I widened
> exhuste 2mm per side with no transfer tining change. Just lightly trimmed. It now runs with 4816 and a pp5020. neck and neck with a hot 350. Someone know why that works so well? She now 4 strokes hard at 14800- 15200 which i barely could 10500 before.What u guys think. Both of these saws have almost 10-15 gal of mix at 40:1 with 93 premium no ethanol..


----------



## smokey7 (Jun 30, 2015)

It ona a test that wemt well. I am very happy with it. I ended up with tons of torque and good holding revs in cut. I sure can lean on it. If i i run it piss revving it i am sure its blowing raw fuel out the exhuste probable from my huge exhuste opening. I am thinking about adding bafels or a pipe for fun to let it.pull some of the raw back into engine. Its a meg gas guzzler it burn way more fuel then my hot 630. Maybe twice as much as a compairson.


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## bikemike (Jun 30, 2015)

Yeah a pipe did wonders om my saw


smokey7 said:


> It ona a test that wemt well. I am very happy with it. I ended up with tons of torque and good holding revs in cut. I sure can lean on it. If i i run it piss revving it i am sure its blowing raw fuel out the exhuste probable from my huge exhuste opening. I am thinking about adding bafels or a pipe for fun to let it.pull some of the raw back into engine. Its a meg gas guzzler it burn way more fuel then my hot 630. Maybe twice as much as a compairson.


----------



## bikemike (Jun 30, 2015)

Yeah a pipe did wonders om my saw


smokey7 said:


> It ona a test that wemt well. I am very happy with it. I ended up with tons of torque and good holding revs in cut. I sure can lean on it. If i i run it piss revving it i am sure its blowing raw fuel out the exhuste probable from my huge exhuste opening. I am thinking about adding bafels or a pipe for fun to let it.pull some of the raw back into engine. Its a meg gas guzzler it burn way more fuel then my hot 630. Maybe twice as much as a compairson.


----------



## smokey7 (Jun 30, 2015)

I am looking at a.pocket pipe forbit to see. I am looking for another 630 or 670 jug also. Can you bridge a open port 625.0or thers like it. What do you do to a open port jug? Does anyone.make flanges for. Piped saws?


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## Chris-PA (Jun 30, 2015)

smokey7 said:


> The clamshells i did poulan 3314 and eager beaver. I made a new lower pan with a cmm machine and a program on the cnc. I moved up the bearing pockets up.050 and and welded a .020 popup. I dont know what the port timing, is just it now blows 227psi with .019. Squish now and runs a 18" bar no problem. I widened
> exhuste 2mm per side with no transfer tining change. Just lightly trimmed. It now runs with 4816 and a pp5020. neck and neck with a hot 350. Someone know why that works so well? She now 4 strokes hard at 14800- 15200 which i barely could 10500 before.What u guys think. Both of these saws have almost 10-15 gal of mix at 40:1 with 93 premium no ethanol..



Cool! I could draw up a lower pan pretty easily on Inventor, and we now have a plug-in that will basically write the G-codes for the mill. However, I'd have to get time on the machine and get help from the guys in the shop, and everything is set up for production. So I don't think I will go that route.



drf255 said:


> Wouldn't welding a popup piston just be easier Chris?
> 
> I'm intrigued by your work, for sure. It just stinks that it only lasted that long.
> 
> I'd be glad to weld a piston up for ya, just say the word.


Thanks, but thankfully the piston and cylinder are OK and I expect they will run fine. It's just the 3D printed plastic pan filler that I added that was destroyed. 

I don't even know if it does anything, and I'm sure the engine would run great without it so other than dyno testing I'm skeptical that a comparison test would be conclusive enough to be worth the trouble. Nevertheless I went to considerable effort to modify the crank and I'd like to put the modification back - just not with that material.


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## bikemike (Jun 30, 2015)

Well i can say if your going to go with a pocket bike pipe make the header pipe as short as possible it worked wonders on my poulan 46 cc i have a very broad power range now and it sounds good got some vids on you tube mike schlak


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## Mastermind (Jun 30, 2015)

smokey7 said:


> The clamshells i did poulan 3314 and eager beaver. I made a new lower pan with a cmm machine and a program on the cnc. I moved up the bearing pockets up.050 and and welded a .020 popup. I dont know what the port timing, is just it now blows 227psi with .019. Squish now and runs a 18" bar no problem. I widened
> exhuste 2mm per side with no transfer tining change. Just lightly trimmed. It now runs with 4816 and a pp5020. neck and neck with a hot 350. *Someone know why that works so well?* She now 4 strokes hard at 14800- 15200 which i barely could 10500 before.What u guys think. Both of these saws have almost 10-15 gal of mix at 40:1 with 93 premium no ethanol..



Compression my man.........it makes huge differences.


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## Chris-PA (Jul 3, 2015)

So I've been thinking about why the first pieces failed, and my suspicion falls on the attachment system which was just epoxy. Given how completely the stuff was cleared off once it failed it might have been better if I had dimpled the surface under the epoxy. I don't know what got it started, but maybe the epoxy let go in a spot.

Given that, I decided that I'd like a positive mechanical means of attachment, and the way I wanted to do that kind of eliminated an aluminum part. I modified the design to add a lip at the edge that would be confined between the cap and the cylinder. Then I added a hole at the bottom for a locating pin. I decided to make them out of ABS this time, as it is harder and has a higher melting point, and it is sandable.

We've had trouble printing ABS, but I spent some time messing with temperature profiles and reducing the print head speed, and I got it to work pretty well.

I had to bevel the lip on the inside of the cap, and I added two locating pins (which are stainless 2-56 screws):



This is how they fit:






I was mostly happy with how it fit, although I wish I had more locating pins to hold the upper ends against the outside. I was all ready to put it back together with a little adhesive to secure the fillers.

*BUT.......*

There's a little problem. ABS dissolves in gasoline. Which was why I used PETG in the first place! I forgot. I set an extra part in a container of 2-stroke mix and it was getting gooey in 30min. I'll have to wait until Monday to print new ones in PETG, and hope that they won't fail the same as the first ones. I am considering adding additional locating pins if I think I can flex the part onto them.


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## LegDeLimber (Jul 4, 2015)

A step at the end of the pan radius would do wonders for trapping them.
You know you've gotta be thinking about it already.
That taper will still let them loose.
IF the tips (thin tips = most susceptible/saturate-able area) swell any little bit, it's going to push them out.

Plus I'd toss a set in some E-85 "gas" (if available) to see what it does to them.
I'm thinking of the E-85 as a way to push both any susceptibility and the results time. 
[ at least use some of whatever corn-gas that you're tormenting yourself with ]
A warm location for the test container would be preferred also.

The mix oil could even be not getting along with the plastic.
So ditto on immersion testing. 
Just 'nother half dozen mason jars of gunk, huh?
Ain't R&D a hoot!


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## Chris-PA (Jul 4, 2015)

LegDeLimber said:


> A step at the end of the pan radius would do wonders for trapping them.
> You know you've gotta be thinking about it already.
> That taper will still let them loose.
> IF the tips (thin tips = most susceptible/saturate-able area) swell any little bit, it's going to push them out.
> ...


Well, I'll think about the step vs. bevel - there's not a lot of meat on the edge of that cap and a step will cut in further. I was worried about breaking through as it is. I think if the part gets flexible enough to be pushed out by the bevel it won't last anyway. 

The PETG actually has decent resistance to both gasoline and ethanol. 

Not surprisingly the cap is cast with a little be of draft, and so it's a little narrower at the bottom than it is up by the bevels. When I print the replacement parts I'm going to try to accommodate that. It will cause some issues as that was the side I had down on the print bed and now it will no longer be flat.


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## Chris-PA (Jul 6, 2015)

Today I printed the parts again. I modified the design to accommodate the draft of the metal cap. I added ridges to the bottom of the part where it would be elevated off the print bed. I knew it would be a pain to cut them off but I couldn't come up with anything else. 

Here's the drawing:

And here's the printed part:


It took a bunch of cutting, filing and sanding to clean it up but it wasn't too hard to do. Then I added more locating pins:




And here's how they fit:



I glued them in with Seal-All, and bolted the cap to a cylinder until it set. Then I put the engine back together with sealant. Hopefully I'll have the saw back together soon.


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## drf255 (Jul 7, 2015)

That's super nice work there Chris.


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## smokey7 (Jul 7, 2015)

Printers rock!!!!!


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## bikemike (Jul 7, 2015)

I'm too computer phucktarded to use those


smokey7 said:


> Printers rock!!!!!


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## Chris-PA (Jul 8, 2015)

It's all back together and running - I didn't take any pictures of it assembled as it looks just like it did on all the other threads where I've built this saw! It started and seemed to run just like it did before, but it will have to wait until (hopefully) tomorrow before I can put it in wood. I just so happen to have an ash I dropped on Sunday that needs to be bucked up.


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## Chris-PA (Jul 9, 2015)

I got a chance to run the saw in that ash before the daily deluge hit. This was a standing dead ash that was really hard. On my first cuts it was not very fast and it made a lot of dust in addition to chips, and I figured maybe the 91VXL was in need of some touch up. So I put on a 16" bar with some sharp Carlton N1. It was faster, but still made quite a bit of fine dust. I measured 10,800 to 11,800rpm in this first cut:


Then I took a look at the 91VXL, and it wasn't dull. So I put it back on and gave it another try (looks like I cut off the very end of the video - not sure how I did that):

It's definitely loaded more, running maybe 9600rpm, and it cuts slower.

That's all I had time for before before the storm. I played with tuning a bit, and had some vapor lock issues - I didn't really feel like I got it running quite right. Then again, this is different wood than I was running it in and it's quite a bit harder.

But the saw stayed together!


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## Raganr (Jul 9, 2015)

Great work and thread. Keep it up.


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## Chris-PA (Jul 10, 2015)

I put the chain for the longer GB bar on the chain vice this evening, and as usual it's easier to see the condition there than it is on the stump. I won't say it was dull, but it's sharper now! I suspect this is part of the issue I was seeing.


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## mexicanyella (Oct 16, 2015)

This is fascinating stuff; more well-documented experimentation, and in an area that never would have occurred to me. Using a 3D printer to fabricate plastic crankcase inserts! My gray "36cc" Craftsman is a easy-to-start, good-running little saw but yours runs like an animal, and with a 2"longer bar to boot. Really cool.

Hopefully the following digression is okay here since squish-talk seems to have wrapped up...and you may well already know all this but...you made a comment a page or so back about this saw's porting not being ideal for a pipe. I think a two-stroke with any porting, in any state of tune, can benefit from a pipe; it's a matter of sizing and shaping the pipe to work in the engine's operating range...and deciding--as in all things related to the search for more HP--whether you will settle for less power over a broad range of rpm, or more power over a narrow (and probably higher) range of rpm. If you have the ability to weld or braze sheet metal, it would be interesting to see you build a pipe to work with one or more of your saw(s).

You know your port timing, which would give you a starting point in terms of headpipe length and overall length. Headpipe and stinger diameters are pretty much determined by exhaust port area. You could still spend a LOT of time trying to optimize cone angles before finding the ideal configuration--some pipes have compound angles of divergence and convergence, which introduces even more variables--but with the basic diameters and lengths in mind, I'd bet you could whip up something that would be significantly better than a box-shaped muffler with a diffuser and outlet hole in it. Looking at Bikemike's 4620, it seems possible to do it in a way that you could even hold the saw safely and operate it in most positions without burning yourself on it.

My point is, pipes don't exist to make more power at higher rpm; they exist to improve scavenge efficiency and retain fuel in the cylinder at whatever rpm you want. The absolute lack of any two-stroke bike WITHOUT some form of expansion chamber exhaust, even trail bikes, from the 70s on, is evidence that it's worth it even on engines in a fairly mild state of tune, and if it can work over a broad-enough speed range for a trail bike, it can work for a WOT-all-the-time saw engine.

I managed to build pipes that worked on a bike I had without even doing much math, after reading up on how they worked and how the various dimensions affected operating parameters...using info from the early 70s by Gordon Jennings. Using parts of existing pipes saved me having to make my own cones. A .pdf of Jennings' useful "Two-Stroke Tuner's Handbook" and his article "Do You Really Want to Know About Expansion Chambers?" are easy to find on Google. Or I can send them to you if you're interested and haven't seen them already. Clearly, I really wanted to know about expansion chambers.


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## David Young (Oct 22, 2015)

@Chris-PA 
any progress on this?


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## Big Block (Oct 22, 2015)

Thats a running little bastard


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## Chris-PA (Oct 25, 2015)

David Young said:


> @Chris-PA
> any progress on this?


I don't come here much any more so I didn't see your post - but funny you should ask! One of the inserts failed today, and I thought I should document that in case anyone else is tempted to use a 3D printed engine part. 

I've put at least 8 tanks through it, probably more, and it has become my go-to saw for everything. With that GB bar and no spikes it has 19" of exposure, which is at least as long at a couple of my larger saws with 20" bars, and with the lo pro chain it is easily as fast. 

Anyway, the engine isn't damaged and just needs a bit of cleaning. The insert that was still attached is interesting:


This end is on the exhaust side and is the leading edge where the counterweights approach the inserts. Notice how it is eroded and pushed back, though there is no sign of mechanical impact. 


This is the trailing edge and the ledge is still mostly intact. 



This tells me that the inserts were actually doing what I hoped they would - damming up the pressure wave pushed along by the front edge of the counterweights and creating a high pressure area right in front of the transfer opening. Still, it's pretty apparent that these materials are not appropriate for use in an engine. They are too low temperature and don't have the strength. I suspect the temperature is OK when the engine is running, but I pushed the heck out of this thing on 90+ degree days, and I'm assuming the heat soak was the problem. However, the erosion of the leading edge would have been happening while it was running. Today was not hot and I didn't run it that long.

I liked the way it ran too much to give up on this part of it, so I am considering a couple of options. One is to just skip the filler and make a close fitting aluminum edge on the front and back. I'm also thinking about how I could make fillers out of some material more durable. If I do that project it will probably be documented elsewhere.


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## Chris-PA (Nov 22, 2015)

All better now.


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## Moparmyway (Nov 22, 2015)

Now you went all out and blinged with JB ................... NICE !!!!!


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## Chris-PA (Jan 18, 2016)

At the time I posted the pictures above I was not really participating here, so most of the info was put elsewhere. 

I decided that the only appropriate material I have ready access to is JB Weld, but forming it was a problem. I wanted it to fit decently close to the crank all the way around the bottom cap. Then I thought that while the 3D printed parts might not hold up in the engine, they should work as a mold/form for the epoxy. I also decided to use the same cap I had modified for the first attempts, as it had pins inserted that would help hold the inserts. I cut some brass window screen strips to embed into the epoxy. I did one side at a time, after smearing the form and other parts of the cap with silicone grease as a mold release - which basically didn't work at all, so the form got destroyed each time. After googling it I found that car wax is better.

I had a lot of excess to clean/grind/chip off. 

I cut the outer edges off an old cap so that I could clamp the bearings down and be able to measure the clearance to the crank - at least sort of.

Then I decided that the inserts really should extend further up toward the transfers in the cylinder, so I made another form to add an insert there. The car wax worked better on that one. I also did a little grinding to open the access from the barrier to the lower transfers. I did not take a picture of the mold form for the upper inserts, but this is what the initial cast looked like:


The ridges are artifacts of the 3D printing on the form. It turned out I made an error on the shape (I forgot to subtract the distance I moved the crank), so these had to be ground down a bit, and I never took a picture of that. 

The intent of all of this was not really to reduce case volume, as the inserts are too small to matter much there. Rather it was to try to block some of the air pushed by the leading edge of the counterweights, creating a high pressure at the base of the transfers as they open. Basically, an inefficient and weak case blower helping to force air up the transfers. The thin con rod and narrow slot help some too. Of course I have no way to measure if it really does anything, but the saw runs well. It is holding a very consistent 10,500rpm in each of the cuts here:



I'm hoping it will hold together now, and I even bought a matching NOS Craftsman clutch cover so it won't look like such a jalopy any more.


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## bikemike (Jan 18, 2016)

Very nice sounds responsive and strong. Is squish reduction something you would do again on other clamshell saws? I was about check up on this thread and ask what's going on ,then you popped In again.


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## Chris-PA (Jan 18, 2016)

bikemike said:


> Very nice sounds responsive and strong. Is squish reduction something you would do again on other clamshell saws? I was about check up on this thread and ask what's going on ,then you popped In again.


I would do it on any of the Poulans with the rubber caps on the bearings, frankly because you don't need to be that accurate in grinding out the pockets. It was actually not that hard to grind the bearing pockets with a sanding drum on the Dremel if you go slow and carefully, and would be even easier if you just removed enough to tighten the squish. Factory is always around 0.040", so you would only need to take off 0.020" - I took off more here and made a pop-up, but that was probably not worth it. 

On clamshells with machined pockets where steel bearings sit directly you'd need to use some sort of tooling on a lathe or mill. But these bearing pockets are used as-cast, and the rubber+sealant covers up a few sins!

Turning the cylinder wasn't much different from any other. 

I learned that the later 46cc engines used on saws like the PP4620 should have the rubber covered bearings too, but my older 2775 does not.


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## bikemike (Jan 18, 2016)

Chris-PA said:


> I would do it on any of the Poulans with the rubber caps on the bearings, frankly because you don't need to be that accurate in grinding out the pockets. It was actually not that hard to grind the bearing pockets with a sanding drum on the Dremel if you go slow and carefully, and would be even easier if you just removed enough to tighten the squish. Factory is always around 0.040", so you would only need to take off 0.020" - I took off more here and made a pop-up, but that was probably not worth it.
> 
> On clamshells with machined pockets where steel bearings sit directly you'd need to use some sort of tooling on a lathe or mill. But these bearing pockets are used as-cast, and the rubber+sealant covers up a few sins!
> 
> ...


What was the stock comp. And compression after reduced squish. I'm thinking of trying it on my 4620 or a popup


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## Chris-PA (Jan 18, 2016)

bikemike said:


> What was the stock comp. And compression after reduced squish. I'm thinking of trying it on my 4620 or a popup


I'm afraid I don't know - I don't own a gauge. I also don't think that low speed pressure readings mean much in relation to running cylinder pressures are rpm, which is part of why I don't bother.


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## bikemike (Jan 18, 2016)

All that matters us that ur crapsman whoops azz and looks good doing it


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## fordf150 (Jan 18, 2016)

Strange that this popped back up. We were just discussing porting clamshell saws on another site. 

Glad to hear it's still holding together and running good


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## old guy (Jan 19, 2016)

I did one of my 2900s, these have the seperate bearing seals. Squish was .050 and compresion was 138
I decided to take .025 off the base and journals, I did it all with a dowal slightly smaller than the bearing wrapped with 80 grit sandpaper and a flat piece of formica countertop with 80grit on it, I have a lot of my depth mics and measuring tools left from my machinist days so with much measuring I I got the journals down .025 within .001 of each other.
After about 9 hours of sanding, turning & sanding and measuring, the base was down .025, this resulted in a squish of .025 and a comp. of 164.
I did a little porting while I was in there, (my first), I took .020 off the intake skirt of the piston and some off the flywheel key to advance timing.
I did not have the flywheel tight enough and when I tried to start it it kicked back and spun the flywheel off and sheared the key, I put it back on probably about stock position.
It started and I made a few cuts with it, it seems to have much more torque but it was running rich and it was too cold to mess with it.
Time will tell how it comes out, would I do it this way again? probly not.

John


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## bikemike (Jan 19, 2016)

I like the wooden dowEl idea


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## Chris-PA (Jan 19, 2016)

old guy said:


> I did one of my 2900s, these have the seperate bearing seals. Squish was .050 and compresion was 138
> I decided to take .025 off the base and journals, I did it all with a dowal slightly smaller than the bearing wrapped with 80 grit sandpaper and a flat piece of formica countertop with 80grit on it, I have a lot of my depth mics and measuring tools left from my machinist days so with much measuring I I got the journals down .025 within .001 of each other.
> After about 9 hours of sanding, turning & sanding and measuring, the base was down .025, this resulted in a squish of .025 and a comp. of 164.
> I did a little porting while I was in there, (my first), I took .020 off the intake skirt of the piston and some off the flywheel key to advance timing.
> ...


That sounds like a lot of work!

I considered cutting the bottom of the clamshell with a good flat file and just measuring on the corners, much as you did. I'm sure it would have been fine, but I had access to the lathe and was having fun 3D printing the mandrel.

You can get flywheels for the 46cc saws cheap on eBay if you want to replace it, but the key is not really needed anyway.


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## old guy (Jan 19, 2016)

Yeah it was a lot of work, it took at least an hour to pull .005 off the base and without good measuring tools it is useless to even try unless you make templates like you did. I have another stock one just like it so it will be interesting to see how much good all this did, both will be running 14" bars & Stihl P S chain.
I got all my ideas from the threads you and others wrote on these forums, so thanks.

John


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## bikemike (Jan 19, 2016)

old guy said:


> Yeah it was a lot of work, it took at least an hour to pull .005 off the base and without good measuring tools it is useless to even try unless you make templates like you did. I have another stock one just like it so it will be interesting to see how much good all this did, both will be running 14" bars & Stihl P S chain.
> I got all my ideas from the threads you and others wrote on these forums, so thanks.
> 
> John


Yeah you had some good running poulans at Wadena last year


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## Chris-PA (Jan 19, 2016)

old guy said:


> it is useless to even try unless you make templates like you did.


Surprisingly I found that the old bearing with the witness marks left in the rubber cover was a better depth gauge for grinding the pockets that the thing I printed.


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## old guy (Jan 19, 2016)

I did it a little backwards, my depth mike has a square end on it so it will not give me an accurate read to the bottom of the journal, but I took a reading with it and added .025 to that and ground em down to that number, then I ground the base down till I had the original bearing depth again. By the time I got done the names Bridgeport & Southbend were were looming big.

John


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## Jeff Lary (Jan 19, 2016)

Chris-PA said:


> Another video - I wanted to try it out with a more typical bar length rather than the oversized GB bar. This is a bar from a McCulloch that is supposed to be 18", but is actually 17". I got it on a used saw and had to modify it so it would oil, otherwise it was similar to an A041 mount bar. It's 60DL rather than the 62DL typical on Poulans. The chain is WodlandPro (Carlton) lo pro.
> 
> 
> 
> I'm really happy with the way this thing runs. I put the GB bar back on it after a while and have decided that it pulls the longer bar just fine, and oils it well, so I'm leaving that on. I have other lighter saws to use the shorter bars on.



I am coming up from behind here but Chris you did a real good job the saw cuts that Oak like white Cedar.

Edit:
Well I just finished up , I read all of this thread as my nephew has a couple of the wild things I think and you have inspired me if I can get my hands on them . They will not run god only knows why ,..but any who....
Chris in the beginning unless I missed it you did not say how you measured the squish to start with? Did you use solider? if so was it plumbing solider? my electrical solider would not be thick enough to measure a big void like you had. Also I don't have any lathe,.. but I wonder if I could " draw file" the cylinder base down some or sand it down using some sand paper stuck down to a block of Granite countertop I have? Well tanks for your advice in the past and future, you did so cool stuff there ! Jeff


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## Chris-PA (Jan 19, 2016)

Jeff Lary said:


> I am coming up from behind here but Chris you did a real good job the saw cuts that Oak like white Cedar.
> 
> Edit:
> Well I just finished up , I read all of this thread as my nephew has a couple of the wild things I think and you have inspired me if I can get my hands on them . They will not run god only knows why ,..but any who....
> Chris in the beginning unless I missed it you did not say how you measured the squish to start with? Did you use solider? if so was it plumbing solider? my electrical solider would not be thick enough to measure a big void like you had. Also I don't have any lathe,.. but I wonder if I could " draw file" the cylinder base down some or sand it down using some sand paper stuck down to a block of Granite countertop I have? Well tanks for your advice in the past and future, you did so cool stuff there ! Jeff


I don't think I said how I measured it, but I always use solder - usually 0.032" electrical solder which is pretty soft. Typically I will twist two strands of that together so I can measure squish at 0.040" like this one. I've got lots of 0.064" solder around too but never tried it. 

I think you could do this with a sanding drum on a Dremel for for the bearing pockets (note there is a ridge on the outside to position the bearings/crank), using the old bearings as a gauge, and a good flat file and/or flat table and sand paper for the cylinder. If you look at the picture below I measured the thickness at each corner so I could verify how even I got it. Also, the factory cylinder is not machined on the bottom, so it will have a fair amount of variation stock.



This shows the bearings in the cap, but they fit the same in the cylinder and the old center seam is clearly visible on the rubber:


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## LegDeLimber (Jan 19, 2016)

Chris-PA said:


> I'm afraid I don't know - I don't own a gauge. I also don't think that low speed pressure readings mean much in relation to running cylinder pressures are rpm, which is part of why I don't bother.



Looking at those "rubber" bedded bearings and wondering how much of a dynamic squish band is in play here also.

First thought of this as a bit of flippant self mussing and then said to self, hmm tis likely far truer than you'd expect.


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## Jeff Lary (Jan 20, 2016)

Thanks Chris


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## Chris-PA (Jan 20, 2016)

One of the things I wanted to emphasize is that when grinding the bearing pockets you have to go very slow and check often. You are trying to grind a semi-circle freehand after all. I also used the depth gauge on my caliper to measure the distance from the ridge to the bottom of the pocket at the center. This allowed me to make sure I had not gone too far in the middle even before I could use the bearing or the tool I made.



LegDeLimber said:


> Looking at those "rubber" bedded bearings and wondering how much of a dynamic squish band is in play here also.
> 
> First thought of this as a bit of flippant self mussing and then said to self, hmm tis likely far truer than you'd expect.


I also wondered if the rubber covered bearings allow the crank to move, especially since I'm reducing the squish and the clearance to the crankshaft counterweights. I don't really think it moves too much though, as the durometer of that rubber is pretty high and it's compressed quite a bit. It probably does damp out really high frequency movement some.


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## bikemike (Jan 20, 2016)

Only thing I could think of looking at pics on first page. Possibly slot the skirt where transfer ports are located to help open up more passage way for air fuel mix to get to the transfer ports. Not sure if it would make a difference but my mind was wandering


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## Jeff Lary (Jan 20, 2016)

What did you end up with for squish or what would you recommend it should be?


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## Chris-PA (Jan 20, 2016)

bikemike said:


> Only thing I could think of looking at pics on first page. Possibly slot the skirt where transfer ports are located to help open up more passage way for air fuel mix to get to the transfer ports. Not sure if it would make a difference but my mind was wandering


Yeah, I've seen that done. I should look at the cut away engine and see how that might interact with the other things I've done here. The transfers actually extend down pretty far below the piston at BDC, all the way to the bearing. 



Jeff Lary said:


> What did you end up with for squish or what would you recommend it should be?


I ended up with 0.021". It probably could have been less but given all the hand grinding and the rubber covered bearings I was good with that.

http://www.arboristsite.com/communi...a-poulan-clamshell.273087/page-8#post-5226959


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## bikemike (Jan 20, 2016)

Yeah I figured with the width of the crank lobes and narrow passage nearing bdc it looks like it could be a Lil restricted.I honestly can't remember what my 46cc poulan piston looks like but I might practice the squish reduction on my husky 136 and se If I feel confident in my dremel skills to try what you did
this is the saw that still needs more hp runs great and reliable and I mill slabs with it. But want more out of it


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## Jeff Lary (Jan 20, 2016)

I have a 255 poulan pro like the one above I use it for liming after I drop my firewood. I have a question though she kicks back like a mule !`If you don't hang onto the recoil handle tight it will rip the handle through your fingers , hurts like,... well you know. So the timing is off I assume? if I want to fix this which way do I adjust the flywheel? Like if the magnets are lined up with the coil pick up which way would you adjust the flywheel? I really don't know how to ask this intelligently ha ha.


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## Chris-PA (Jan 20, 2016)

Jeff Lary said:


> I have a 266 poulan pro like the one above I use it for liming after I drop my firewood. I have a question though she kicks back like a mule !`If you don't hang onto the recoil handle tight it will rip the handle through your fingers , hurts like,... well you know. So the timing is off I assume? if I want to fix this which way do I adjust the flywheel? Like if the magnets are lined up with the coil pick up which way would you adjust the flywheel? I really don't know how to ask this intelligently ha ha.


My Poulan 2775 does this too. 

In general you would want to retard the spark to make it easier to start, but that is likely to kill the power & throttle response. To retard the timing you would want to rotate it clockwise in relation to the crankshaft (when viewed from the flywheel side). Maybe use better gloves or get one of those giant D handles I see on some saws?


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## bikemike (Jan 20, 2016)

I did read up on the naked lady machine that making the air gap of a coil a bigger gap can retard the timing ever so slightly cause it takes that much longer for the magnetic field to make its cycle through the iron plates. I don't know if it would be a noticeable difference in timing


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## Jeff Lary (Jan 21, 2016)

Well I can live with it instead of loosing power. The only real issue is it is hard on the recoil I think.


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## jdrepair (Jan 22, 2016)

Hi everyone this is the first time I have put anything on here. I been a long time mechanic on all sorts of different equipment and been into various hi performance hobbies especially tractor pulling so needless to say im never happy leaveing anything I own stock lol and I always enjoy building up something others say is junk into something impressive. I cut wood to heat my garage and I began with a poulan 2900 someone gave me that didnt run that I resurrected. That one poulan turned into a dozen and a few huskeys. I been doing muffler mods and simple improvements that really helped these saws. Raiseing the compression has been in the back of my mind for some time and last night I ran across this thread and what chris did is just what I had been thinking about so reading this gave me the confidence to try it. I took a 42cc craftsman measured the squish at 35 tho I surfaced the jug with a belt sander intended for wood I took it down 40 tho then deepend the bearing journals how chris did and turned the outer portion of the piston down 20 tho to make a dome. I started with 115 psi comp and now have 130 I also ported the exhaust port. Made a test cut tonight and wow what a difference. I now need to grind up an aggressive chain and see what it will really do. Sorry for the long post just wanted to introduce myself and thank everyone here for shareing the great info here and I wanted to share my findings also its good to know others are thinking outside the box like I like to do lol


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## Chris-PA (Jan 22, 2016)

jdrepair said:


> Hi everyone this is the first time I have put anything on here. I been a long time mechanic on all sorts of different equipment and been into various hi performance hobbies especially tractor pulling so needless to say im never happy leaveing anything I own stock lol and I always enjoy building up something others say is junk into something impressive. I cut wood to heat my garage and I began with a poulan 2900 someone gave me that didnt run that I resurrected. That one poulan turned into a dozen and a few huskeys. I been doing muffler mods and simple improvements that really helped these saws. Raiseing the compression has been in the back of my mind for some time and last night I ran across this thread and what chris did is just what I had been thinking about so reading this gave me the confidence to try it. I took a 42cc craftsman measured the squish at 35 tho I surfaced the jug with a belt sander intended for wood I took it down 40 tho then deepend the bearing journals how chris did and turned the outer portion of the piston down 20 tho to make a dome. I started with 115 psi comp and now have 130 I also ported the exhaust port. Made a test cut tonight and wow what a difference. I now need to grind up an aggressive chain and see what it will really do. Sorry for the long post just wanted to introduce myself and thank everyone here for shareing the great info here and I wanted to share my findings also its good to know others are thinking outside the box like I like to do lol


Cool! I'm glad to see others try it. I know of a couple of others who have ground out the bearing pockets on these through various methods, and they run pretty well.


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## Chris-PA (Jul 31, 2016)

While I was using this saw today it started acting erratically, revving at idle and all over the place. That turned out to be a loose carb mount block, but while looking for that I happened to notice what looked like arcing marks on the flywheel magnets. I though that was rather odd! So I looked into that further, and polished them off with some Scotchbrite - it was certainly from arcing. 

First I figured maybe the coil/module was bad, so I pulled it off. While cleaning it up to put the replacement module in, I realized the metal strap that connects the ignition core lamination to the engine was missing - I had forgotten to put it back when I assembled it last! So in order to fire the plug it had to arc back to the coil lamination in addition to arcing across the plug gap. I'm sure that just did _*wonderful*_ things to the bearings! 

The flywheel is of course connected to the moving portions of the engine, and the plug is connected to the stationary cylinder, so electrical connection needed to be made between the crank/rod/piston assembly and the cylinder. Because the main crank bearings are rubber coated there isn't much connection there. Maybe it arced through the ball bearings and that rubber coating, but more likely it passed through the roller bearings from the crank to the rod to the piston, and then through the ring or piston to the cylinder wall. Anyway, I have no doubt some pitting went on along that path, and I'm not very happy about it - but I didn't put a lot of hours on it since the last rebuild and I'm not pulling it apart now. It's running great. 

I am still amazed it ran like that, although I wish it hadn't.


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## HuskStihl (Jul 31, 2016)

Crazy


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## heyduke (Jul 31, 2016)

Chris-PA said:


> While I was using this saw today it started acting erratically, revving at idle and all over the place. That turned out to be a loose carb mount block, but while looking for that I happened to notice what looked like arcing marks on the flywheel magnets. I though that was rather odd! So I looked into that further, and polished them off with some Scotchbrite - it was certainly from arcing.
> 
> First I figured maybe the coil/module was bad, so I pulled it off. While cleaning it up to put the replacement module in, I realized the metal strap that connects the ignition core lamination to the engine was missing - I had forgotten to put it back when I assembled it last! So in order to fire the plug it had to arc back to the coil lamination in addition to arcing across the plug gap. I'm sure that just did _*wonderful*_ things to the bearings!
> 
> ...



yeah, that little grounding strap is easy to miss. you could run a wire from the metal top end to a module mounting screw, like a stihl 029. it's easy to imagine that strap getting lost while you're de-crustifying a dirty saw. and getting it back in is 3-d tetris. i always figured that it wouldn't fire without that strap, amazing. will you need to replace the flywheel or module?


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## Chris-PA (Aug 1, 2016)

heyduke said:


> yeah, that little grounding strap is easy to miss. you could run a wire from the metal top end to a module mounting screw, like a stihl 029. it's easy to imagine that strap getting lost while you're de-crustifying a dirty saw. and getting it back in is 3-d tetris. i always figured that it wouldn't fire without that strap, amazing. will you need to replace the flywheel or module?


I normally do not remove that strap but I had put helicoil inserts into the plastic case for the ignition screws as well as the recoil, since the threads were starting to strip out. I suspect that may have been when I forgot it. 

I did replace the ignition module just to be cautious and because I had another, but I don't think there was anything wrong with it.


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## 7sleeper (Aug 2, 2016)

Report back to tell us if it runs different.

7


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## Chris-PA (Aug 8, 2016)

7sleeper said:


> Report back to tell us if it runs different.
> 
> 7


It seems to run fine. I decided to make it work:



That's white ash and a 68DL 19" bar with Oregon 91VXL. It's mostly running about 9500rpm, but since it's loaded pretty heavy it varies a bit.


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## SalahHH83 (Aug 31, 2016)

This is awesome, Chris! Great ingenuity! I love projects like this and you've really done a great job with this.


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## Chris-PA (Dec 30, 2018)

It's been a while since I posted here as I've moved on to other things, but I had to tear this saw apart so I thought I'd stop by and give an update. The main issue was that I just could not keep the bolts for the carb mounting block tight, no matter what I tried they backed off and the carb would get lose. I could always tell because I would have to keep enriching the H and the idle would start creeping up - damned annoying when I'm trying to work!

Eventually I decided the threads must have become loose and polished from so many teardowns, and I had to drill it for some Helicoils so I could use M5 x 0.8 cap screws and LocTite them in. I figured once I had the engine out I'd open it up to see how the JB Weld inserts were holding up.

Here is the cap - it's lost a bit of the thin epoxy in the center (not as much as it appears as I picked a bit more out). It's gotten sort of brown, but seems to be holding up:



Here are the ones I formed in the cylinder - they don't have any screws to reinforce them like the cap does:



I decided to do one more mod while I had it apart - I added some notches in the piston skirt right at the transfer entrance, because the big fat counterweights really block that up at BDC. I've done this on other Poulans since I built this and they worked well. They are 0.125" high and the width of the transfer runner:



Oh, and I did the inserts too:



It also got new bearings and seals since I had some around. It seems to run quite well, and it feels like it might be pulling even better with the transfer notches. Time will tell if the carb stays on.

Anyway, take care and have a happy 2019 - I'll check this thread for a bit but don't plan to stay around too long.


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## Justin Taylor (Dec 30, 2018)

Is is one cool thread iv been moding my wildthing for a long time now and been runing out of carbs to use i got the saw up to 20'000 rpm on accident but what carb did u use?


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## Chris-PA (Dec 30, 2018)

Justin Taylor said:


> Is is one cool thread iv been moding my wildthing for a long time now and been runing out of carbs to use i got the saw up to 20'000 rpm on accident but what carb did u use?



I believe it's a WT-391, which is stock on the versions with A/V. It's been bored out to about 14mm. 20k would be extreme indeed! I keep a 19" (68DL) bar on this so it won't rev to the moon, but it pulls it well.


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## Justin Taylor (Dec 30, 2018)

Chris-PA said:


> I believe it's a WT-391, which is stock on the versions with A/V. It's been bored out to about 14mm. 20k would be extreme indeed! I keep a 19" (68DL) bar on this so it won't rev to the moon, but it pulls it well.


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## Justin Taylor (Dec 30, 2018)

What part did u bore out to 14mm? See woth my stock carb witch workes the best i have the h screw max so i can get the saw to run super fast like 16k rpms and idels at 7k or idels at 4k and only goes to 7k rpm so


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## Chris-PA (Dec 30, 2018)

Justin Taylor said:


> What part did u bore out to 14mm? See woth my stock carb witch workes the best i have the h screw max so i can get the saw to run super fast like 16k rpms and idels at 7k or idels at 4k and only goes to 7k rpm so



I bored out the venturi - this is the thread where I was working on that: https://www.arboristsite.com/community/threads/boring-out-a-carb.296271/ I'm not all that sold on bored out carbs anymore, but this one went from 11mm to 14mm which was useful. 

Usually running that high requires some lean mixtures which are liable to burn it up. Are you talking about no load rpm? I'm more interested in how they run under load, as I use my saws for firewood.


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## Justin Taylor (Dec 30, 2018)

This is mostly with no load but have been trying to get a big carb for loaded work


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