# Cylinder Porting for Dummies....



## teacherman (Jan 9, 2009)

I have followed with interest the various threads on porting saws to improve performance. I am still scared to tackle it, because I don't really know what to do. I know that widening ports is a start, but raising and lowering teh intake and exhaust timing, and the transfers, well, I don't git it. I used to be a professional sculptor, and I have used mini die grinders and the like on stone for years. Would anybody feel like posting a basic how-to that breaks it down in terms that are easy to understand, a tutorial, if you will? I think it would make a great sticky thread, butt that is JMO

Yes, I have searched, and I guess I am in the Special Ed class when it comes to porting. Many thanks.

I have an extra 026 I can practice on, and a 10 lb. orange and white screamer would be cool to have out in the woods on firewood day.


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## 7oaks (Jan 9, 2009)

teacherman said:


> I have followed with interest the various threads on porting saws to improve performance. I am still scared to tackle it, because I don't really know what to do. I know that widening ports is a start, but raising and lowering teh intake and exhaust timing, and the transfers, well, I don't git it. I used to be a professional sculptor, and I have used mini die grinders and the like on stone for years. Would anybody feel like posting a basic how-to that breaks it down in terms that are easy to understand, a tutorial, if you will? I think it would make a great sticky thread, butt that is JMO
> 
> Yes, I have searched, and I guess I am in the Special Ed class when it comes to porting. Many thanks.
> 
> I have an extra 026 I can practice on, and a 10 lb. orange and white screamer would be cool to have out in the woods on firewood day.



+1 from me...Carl


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## FELLNORTH (Jan 9, 2009)

Would Like The Same Info...
Thanx For Posting


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## blsnelling (Jan 9, 2009)

That is what I tried to do in the 361BB porting thread. What additional info are you looking for? LINK


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## teacherman (Jan 9, 2009)

I guess I am just slow. I see the pics, I see the ovals drawn on pistons, but I don't see how to configure the ports, where to grind. When you talk about timing, I dont know if you grind on the top or the bottom of the port, and I stihl have no idea whatsoever to do on the transfers. Maybe I am just challenged on the written descriptions, thus the thread title. Step by step how-tos are a pain in the bu††ox to put together, if they really explain it to dummies.

A big concern for me is the nikasil coating and the bevel.. I imagine the bevel was there before the coating was applied, and any port expansion inside the cylinder means the coating is ground off the bevel, and there seems to be a risk of the piston ring peeling the coating, because the bevel you cut when porting will have no nikasil on it.


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## blsnelling (Jan 9, 2009)

teacherman said:


> I guess I am just slow. I see the pics, I see the ovals drawn on pistons, but I don't see how to configure the ports, where to grind. When you talk about timing, I dont know if you grind on the top or the bottom of the port, and I stihl have no idea whatsoever to do on the transfers. Maybe I am just challenged on the written descriptions, thus the thread title. Step by step how-tos are a pain in the bu††ox to put together, if they really explain it to dummies.
> 
> A big concern for me is the nikasil coating and the bevel.. I imagine the bevel was there before the coating was applied, and any port expansion inside the cylinder means the coating is ground off the bevel, and there seems to be a risk of the piston ring peeling the coating, because the bevel you cut when porting will have no nikasil on it.



I actually talk about most of that stuff in that thread. The only way to learn is to get in there and start doing it. It'll start to make sense once you have the cylinder in your hand and reread the thread.

Here's what I recommend for starters.

Don't do anything to the transfers, period. You can make tremendous gains without modding them.

Do not raise or lower the intake or exhaust ports. Widen them only. Mark the ports on the piston skirt and then widen them so that there's only about 1/16" left to seal the port. DON'T go any farther though. Keep in mind you have to rebevel the port too. You also have to watch out for where the ring ends are. They are often right at the edges of the port. In that case you may not be able to go as close to the edge of the skirt. You MUST leave cylinder wall for the rign to ride on as it goes past the port window! I wouldn't leave less than 1/8".

Remove the casting lines from the windows in the piston. Also angle them on the inside as I have shown in the 361BB porting thread.

Don't make the roof or floor of the ports too flat. The flatter they are, the more area you open the fastest. But go too flat and you're likely to catch a ring even after beveling.

Make the walls of the ports straight up and down. If you leave them curved, you're not opening the port area as qickly as possible at a given point in the rotation of the crank. You want maximum area as soon as possible. A totally square port would be the max but won't work as described above. It's a balancing act.

Use a round stone to rebevel the ports. You don't need a huge angle. It only needs to be a few thousanths deep. The ring doesn't go into the port window that far. Just lightly round off the edges of the port so that the ring won't catch on it.

Reassemble the engine using a gasket made of any paper or soft metal that will give you a squish of about .020". I've used get well card, pop can cases, etc.. Make sure to use a fuel resistant sealer like Threebond 1104/1194. 

A little about port timing. Port timing on the exhaust port is measured off of the roof, closest to the combustion chamber. The critical point is where the port window first opens as it travels from TDC. Do not lower the floor. You may have the port open with the piston at TDC. That's not desireable and lowering it will give you no performance gains.

Intake timing is measured from the floor of the port. That's why some "port" the intake by removing material from the bottom of the skirt of the piston. It's best to lower the port when needed. Again, you don't need to do this on your first saw. Do not raise the roof or the rings may drop below the top of the port and catch. Some actually drop below by design, but there's no gain to be had by raising the roof of the intake.

Correct me where I may be wrong guys. I've only been doing this a couple years.


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## teacherman (Jan 9, 2009)

Thanks, Brad. I do appreciate it. I still don't quite get teh numbers you post for the degrees of rotation on that thread. Is 0˚ TDC, and all the numbers are after or before TDC, or is there another reference point?


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## Lakeside53 (Jan 9, 2009)

Good write up Brad... 

I differ on one small point - don't just use "anything" for a gasket. A gasket must not compress over time or (particularly on bigger saws) you'll end up with loose cylinder bolts and maybe cracked cylinders. Sure, almost anything will work for some period of time, but will it last?

If you have to use paper (verses a coated metal gasket), use real gasket material.


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## blsnelling (Jan 9, 2009)

I hear you Andy. I know that was a problem with the old paper gaskets Stihl used to use and is likely why they now use coated metal. Blown out paper gaskets probably led to the demise of more than one saw. I actually used a paper grocery bag on my 084. I need about .008 and that fit the bill. I'm sure I would be well advised to check to make sure they're still tight after a while. Probably right now after the first few heat cycles would be a good time.


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## 7sleeper (Jan 9, 2009)

blsnelling said:


> .....Correct me where I may be wrong guys. I've only been doing this a couple years.



your all wrong! 




just kiddin 

I wish I only knew what you wright about!

greetings from Austria (& from work another 24hr shift  )

7sleeper


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## blsnelling (Jan 9, 2009)

You can learn it too. It's just picked up from reading here and elsewhere, doing some work, posting lots of pictures and getting feedback, making changes, etc.. It's an evolutionary thing. I'm just now starting to play around a little more with port timing numbers and working on the transfers a litte more. There's a whole science to this madness that's way over my head. I don't understand all the 2-stoke theory, but have a steady even hand and improve on what's already there.


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## Lakeside53 (Jan 9, 2009)

Next you'll be buying a mill, tig, bandsaw, lathe.. and... and... and.. you'll soon realize that CAD was inexpensive in comparison


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## Tree Sling'r (Jan 9, 2009)

I would not even worry about squish and gaskets at this point, just get a concept of porting.
Leave your squish and gasket the way it is, that way you are not stressing over port timing, which is way over blown at this point.
Get your gains like Brad stated, from widening your ports. Even if you knock the coating off of the ports and smooth it up it will run better.

A basic mod:

Widen the exhaust, raise it by knocking off the coating, smooth it out.

Widen, and lower the intake by knocking off the lip, then leave it rough, but even of course.

Take and remove the lip from the lower transfers so that by feeling it and looking at it, it will obviously flow better.

Just by comparing the before and after - you want better flow and smoothness of the ports.

Don't get crazy, a little goes a long ways.

A porting tool with a abrassive bit will knock off the coating. Once the cotaing is knocked off you can use a round rasp and a chainsaw file on the aluminum with amazing results.

Bevel the ports with a lapradory needle file or a grit stone ball, smoth out with sandpaper, what ever. I use a ball, needle file, then a hone.


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## TRI955 (Jan 9, 2009)

Great info for us "dummies"....I think I'm gonna work on the 377 over the weekend.....


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## blsnelling (Jan 9, 2009)

Tree Sling'r said:


> I would not even worry about squish and gaskets at this point, just get a concept of porting.
> Leave your squish and gasket the way it is, that way you are not stressing over port timing, which is way over blown at this point.



Excellent advise for a beginner. Most of the gains are found in flow improvments rather than compression increases. I think Tree Sling'r ports with an emphasis on torque as well. All those RPMs won't help you if you can't maintain them in the cut.


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## bowtechmadman (Jan 9, 2009)

Good post guys...appreciate the info...nervous myself about trying it the first time.
I think it would make for a good GTG...porting 101.


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## blsnelling (Jan 9, 2009)

In all seriousness, you won't learn until you do it yourself. At least that's the way I am. I have to lear hands on. Start with a saw that isn't so expensive. A 260 isn't cheap but it's a lot cheaper than a 660 or 084. I use my 260 as my test bed. I'll try things on it before I will my other saws. Post up your work and let us look at it. We'll try to steer you in the right direction. It's a lot easier if you post the pics in the forum here. That way you get more input and a more balanced approach. We all do things a little differently and can learn from each other.


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## teacherman (Jan 9, 2009)

I'll get started at some point and definitely post pics. This weekend I have to start a huge hollow tree removal in my yard, it will be a lot of roping down over houses and such. I know my AC bill will be higher, and I guess my dream of a 40 foot high treehouse will have to wait a while....

Brad and Treeslinger, thanks for the info and simplification! Even ol Edward (special Edward, that is) can port a saw now! ¡Muchas gracías!

Edward


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## blsnelling (Jan 9, 2009)

teacherman said:


> Even ol Edward (special Edward, that is) can port a saw now! ¡Muchas gracías!
> 
> Edward



So you ready to tear into that 084 or what?:greenchainsaw:


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## teacherman (Jan 9, 2009)

blsnelling said:


> So you ready to tear into that 084 or what?:greenchainsaw:



At least the size would make it easier to get in there and grind on it.
Do you still have the link to the thread about that saw? I am trying to remember, doesn't it have the rev limited coil? If so, it would have to be a torque-heavy port job, which wood make it more like an 090......


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## troutfisher (Jan 9, 2009)

Just my opinion, but I feel that if I'm not going to raise the compression on a woods port, it's not worth doing. Just mod the muffler and run it.


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## teacherman (Jan 9, 2009)

Brad, if you look at an optimally ported cylinder from the top, and if you took a cross-section so you could see the port from the top, would the sidewalls of the port space be relatively straight, or would the port space have more of an hourglass shape?

I know the opening into the cylinder is to be an oval, I mean the space between the port openings. Thanks.


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## Boleclimber (Jan 9, 2009)

Below is a link to a discussion discussing 2 stroke books. I recommend you use the search function for the words port timing, duration, porting and any other word associated with porting a chainsaw. 

Using the search function and purchasing two books on 2 strokes I was able to learn enough information to woods port my saws. This worked for me and will work for you. The largest step is taking the risk and diving into a project, you will learn quick.





http://www.arboristsite.com/showthread.php?t=4175&highlight=tuning+books


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## blsnelling (Jan 9, 2009)

teacherman said:


> Brad, if you look at an optimally ported cylinder from the top, and if you took a cross-section so you could see the port from the top, would the sidewalls of the port space be relatively straight, or would the port space have more of an hourglass shape?
> 
> I know the opening into the cylinder is to be an oval, I mean the space between the port openings. Thanks.



Straight side walls if at all possible. That way you get maximum port width the fastest as the port opens.


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## Tree Sling'r (Jan 9, 2009)

troutfisher said:


> Just my opinion, but I feel that if I'm not going to raise the compression on a woods port, it's not worth doing. Just mod the muffler and run it.



I have gotten pretty good compression numbers just by widening ports.


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## blsnelling (Jan 9, 2009)

This 361BB was the first time I ever significantly raised an exhaust port. But it was really low to begin with and did not have the port timing I wanted.


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## troutfisher (Jan 9, 2009)

Tree Sling'r said:


> I have gotten pretty good compression numbers just by widening ports.



Usually step one for me is setting the squish and see what I get for compression, If I'm not happy I go to a pop up piston. I guess I've never tried widening first. Does compression raise much just widening the ports? Usually I'm looking for at least another 50psi on the guage. Thanks for sharing this Sling'r.


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## blsnelling (Jan 9, 2009)

Widening the ports will do nothing to affect compression. I'd love to have a mill and lathe to do popups and the like.


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## lovetheoutdoors (Jan 9, 2009)

great info here...thought about some tinkering myself. can someone post a pic of the main tools you grind with like the grinding stones and so forth...i have several die grinders i just need to know the size and shape of the attachment you guys are using.


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## blsnelling (Jan 9, 2009)

Nothing but a corded Dremel with a carbide burr, 1/4" diameter cylinder radius-tip double-cut. Finish shaping up and flaten out with a chain sharpening file. Use sand paper to finish.


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## parrisw (Jan 9, 2009)

Remember to measure to the narrowest part of the skirt. Unlike I did and measured to the bulge of the skirt, and farked up a good 395 cylinder.


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## Martinm210 (Jan 10, 2009)

I still don't understand what timing to look for, but I have experimented with some tools. I found my dremel with the pencil extension to work best for me as the grinder. One of those micro pencil die grinders would probably also work really well, but the dremel seems to have enough power.

The other thing I found is for polishing. They sell these little brown and blue polishing bits that work pretty well for polishing. I found them at harbor freight for $2 for a six pack.

Anyhow, after redoing the exhaust port about three times I finally started using this sort of method:
1) Grind with either sanding drums or carbid bits, sanding drums seem to work best when cutting down the coating as it's pretty hard and sand is harder than carbide. Just rough it out with these bits, and don't try to get it perfect, it won't be smooth or straight, that's where the needle files come in.
2) Needle files work great to take the rough cutting down to a nice flat surface. They leave a rough finish, but it's straight which will show later
3) Wrap sand paper on the needle files and sand. Seems like I start with 150, then 220 grit paper. That's plenty good for intake ports, but exhaust you can continue, sand down to 400
4) polish with those little brown and blue polishing bits. They were down to nothing fast, but they work much faster than any cotton buffs and compound.
5)finish with some compound and a soft cloth by hand.
6) Chamfer edges of ports with a ball stone, then polish those same edges with a round blue polishing bit. I still worry about the coating missing on the chamfer, so I figured a nice polishing is a worthwhile second step.
7)Wash it all up and check with a ring for level. Probably to do a good job, you'd need to check and touch up several times until everything was perfectly symmetrical.

Last but not least take your time. I still managed to slip up twice doing my piston and made a few nicks where I didn't want them. I'm hoping my light sanding will have taken care of that.

Anyhow, I didn't go too far with my first one. Mainly just clean up the ports and spent most of my time port matching the muffler and cleaning up the piston windows. I'll do my MS290 as soon as they come out with a 390 kit..


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## Tree Sling'r (Jan 10, 2009)

troutfisher said:


> Usually step one for me is setting the squish and see what I get for compression, If I'm not happy I go to a pop up piston. I guess I've never tried widening first. Does compression raise much just widening the ports? Usually I'm looking for at least another 50psi on the guage. Thanks for sharing this Sling'r.



I guess I should have followed through with my statement:
You don't have to lower your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.


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## troutfisher (Jan 10, 2009)

Tree Sling'r said:


> I guess I should have followed through with my statement:
> You don't have to lower a your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.



Yup, that's where I like squish readings at too.....and stock numbers usually work good for work saws. If I deck the jug and cut the popup on the piston, and compression goes way high, I'll raise the exhaust a bit to keep it down around 190psi. Big changes in timing numbers usually go along with pipes and heads and stuff like that.


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## volks-man (Jan 10, 2009)

blsnelling said:


> Widening the ports will do nothing to affect compression. I'd love to have a mill and lathe to do popups and the like.





Tree Sling'r said:


> I guess I should have followed through with my statement:
> You don't have to lower your squish a bunch to get high compression readings. The last 5 460s I have built have had the squish set at .023-.025 with compression @ 195-210lbs. Granted a little bit of that is coming from a pop up on the piston, but not that much. Just raising ports back up to stock numbers.



hey guys,
since this is the 'dummies' thread...
would you mind explaining the pop-up?
you machine off a ring of material around the top edge of the piston right?
how does this raise compresion? 
thanks,

_one of the dummies._


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## Martinm210 (Jan 10, 2009)

How do you go about raising the bottom of an exhaust port. If I were to mill down the base of my jug and turn the piston to make a pop up, I'd have a problem with the bottom of the piston skirt clearing the bottom of the exhaust port on my 066BB kit (Is that the sub piston induction term?). It already does a very small amount.

Is JB weld or something else used to fill in stuff like that?

Obviously the fill would need to remain away from the piston enough to prevent contact.

A longer piston would do the trick too, but I'm not sure what would be compatible in 56mm.


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## Tree Sling'r (Jan 10, 2009)

Martinm210 said:


> How do you go about raising the bottom of an exhaust port. If I were to mill down the base of my jug and turn the piston to make a pop up, I'd have a problem with the bottom of the piston skirt clearing the bottom of the exhaust port on my 066BB kit (Is that the sub piston induction term?). It already does a very small amount.
> 
> Is JB weld or something else used to fill in stuff like that?
> 
> ...



If you cut the base and make the pop up the same you should not have any issues. But, then again, the BB kits are weird. Waste of money if you ask me.


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## Tree Sling'r (Jan 10, 2009)

volks-man said:


> hey guys,
> since this is the 'dummies' thread...
> would you mind explaining the pop-up?
> you machine off a ring of material around the top edge of the piston right?
> ...



The pop up goes into the compression chamber, creating more compression.


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## Lakeside53 (Jan 10, 2009)

If you don't want to grind on a cylinder, or lathe a pop-up.


I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....

How about building up the top of the chamber with a tig, then grinding it smooth with a big ball cutter?


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## Martinm210 (Jan 10, 2009)

Lakeside53 said:


> If you don't want to grind on a cylinder, or lathe a pop-up.
> 
> 
> I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....
> ...



Neat idea! Just a slightly over length plug hmmmm...


Has anyone tried cutting the jug into separate head pieces?

Maybe with some careful measuring and a nice large thin kerf slitting saw, you could make it happen on a mill?

Ahh probably too much headache, but it would allow some more tinkering with compression/domes without messing with your port timing.


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## scotclayshooter (Jan 10, 2009)

Lakeside53 said:


> If you don't want to grind on a cylinder, or lathe a pop-up.
> 
> 
> I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....
> ...



Would the exposed threads not make hot spots and cause pre ignition?
I remember Doug Miller tried somthing similar for variable compression but dismissed it eventually.


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## Carlyle (Jan 10, 2009)

Don't know if this will help but TW has a pic of a pop-up in this thread, I think that it is on page 2. Timberwolf is over my head on the whole porting thing, so I will just leave it up to him.





volks-man said:


> hey guys,
> since this is the 'dummies' thread...
> would you mind explaining the pop-up?
> you machine off a ring of material around the top edge of the piston right?
> ...


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## scotclayshooter (Jan 10, 2009)

Martinm210 said:


> Neat idea! Just a slightly over length plug hmmmm...
> 
> 
> Has anyone tried cutting the jug into separate head pieces?
> ...



Look up Timberwolfs old posts he seems to have done everything you can think of and seperate heads is one of them.


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## Lakeside53 (Jan 10, 2009)

scotclayshooter said:


> Would the exposed threads not make hot spots and cause pre ignition?
> I remember Doug Miller tried somthing similar for variable compression but dismissed it eventually.



Possibly, but I didn't notice any. It was a saw in for service so I don't know the history. I can't even remember if the threads has been removed on the end. 

There was an old tech note on the 075 where they discussed removing the decomp valve and plugging the hole to raise compression and HP. I'll need to dig it out to refresh my old memory what they actually said though!


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## Tree Sling'r (Jan 10, 2009)

Lakeside53 said:


> Possibly, but I didn't notice any. It was a saw in for service so I don't know the history. I can't even remember if the threads has been removed on the end.
> 
> There was an old tech note on the 075 where they discussed removing the decomp valve and plugging the hole to raise compression and HP. I'll need to dig it out to refresh my old memory what they actually said though!



I plug all of my saws as well as others, and I do think it helps compression.


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## 04ultra (Jan 10, 2009)

I had a kart guy (kt100) tell me that in a few classes that they put longer reach spark plugs in to take up space in the combustion chambers to raise the comp a little ...



.


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## scotclayshooter (Jan 10, 2009)

Tree Sling'r said:


> I plug all of my saws as well as others, and I do think it helps compression.



With those saws over 195 psi they must take a fair old tug to get them going without a de-comp:jawdrop:


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## 04ultra (Jan 10, 2009)

Lakeside53 said:


> Good write up Brad...
> 
> *I differ on one small point - don't just use "anything" for a gasket. A gasket must not compress over time or (particularly on bigger saws) you'll end up with loose cylinder bolts and maybe cracked cylinders. Sure, almost anything will work for some period of time, but will it last?*
> 
> If you have to use paper (verses a coated metal gasket), use real gasket material.













*3120 P/C's are spendy when the cylinder bolts come loose .........*



.


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## epicklein22 (Jan 10, 2009)

This is a fun thread. Lots of information being tossed around. Thanks to all the guys answering them. I am definitely gonna try porting a saw this year. Probably around summer when I have more cash flow and time. Now to find a test subject and a dremel, plus buy some bits and I should be in business.


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## blsnelling (Jan 10, 2009)

volks-man said:


> would you mind explaining the pop-up?
> how does this raise compresion?


When you cut the crown of the piston around the edges, you can then lower the cylinder even farther. Then the raised center section of the piston sticks up into the combustion chamber displacing volume. The less volume there is in the combustion chamber, the higher the compression is.



Martinm210 said:


> How do you go about raising the bottom of an exhaust port. If I were to mill down the base of my jug and turn the piston to make a pop up, I'd have a problem with the bottom of the piston skirt clearing the bottom of the exhaust port on my 066BB kit (Is that the sub piston induction term?). It already does a very small amount.
> 
> Is JB weld or something else used to fill in stuff like that?
> 
> A longer piston would do the trick too, but I'm not sure what would be compatible in 56mm.


This is a factor you always have to keep in mind when lowering the cylinder. A longer piston skirt is the only answer I know of. I seriously doubt JBWeld would hold up in those kinds of temps. My 066BB slightly free ports at TDC as well. Turning a popup on the piston and lowering the jug more is simply not an option. It's a limitation of that kit. I have seen the crown of a 066BB piston build up with TIG welding and then turned down, resulting in a .060" popup. Last I heard it was running fine. I hate adding mass to the piston, but you've got to do what you've got to do.



Lakeside53 said:


> I saw a pretty interesting way to raise compression - take out the decomp valve and wind in a bolt that protudes even slightly into the cylidner. Sure make a difference. I suspect it messes with gas flow though... However.. the saw ran remarkably well....


I'm going to give this a try!



Martinm210 said:


> Has anyone tried cutting the jug into separate head pieces?


Racers do it all the time. They machine the head off of the jug and build an entirely new head from billet aluminum. That way they can create the combustion chamber any size they want and get whatever compression they want.



Tree Sling'r said:


> I plug all of my saws as well as others, and I do think it helps compression.


My 076 Super has no decomp and it starts easily with an Elastostart. My 084 is a little more demanding.


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## volks-man (Jan 10, 2009)

blsnelling said:


> When you cut the crown of the piston around the edges, you can then lower the cylinder even farther. Then the raised center section of the piston sticks up into the combustion chamber displacing volume. The less volume there is in the combustion chamber, the higher the compression is.



thanks. gotcha!
i had missed the part where you lower the cylinder.


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## PatrickIreland (Jan 10, 2009)

Should be stickied or at least linked to, IMO as a newbie. 4-strokes I can tune up all day long, but for the past 20 years the only 2-stroke things I've had to mess with are outboards and lawnmowers - either of which I'd dump at a shop to be fixed. I don't want mt outboard quitting on me, and my lawnmower? hell, I only use it about once a year anyway, I don't expect it to start!



blsnelling said:


> I actually talk about most of that stuff in that thread. The only way to learn is to get in there and start doing it. It'll start to make sense once you have the cylinder in your hand and reread the thread.
> 
> Here's what I recommend for starters.
> 
> ...


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## Wet1 (Jan 10, 2009)

Excellent basic info on porting Brad!


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## volks-man (Jan 13, 2009)

ok porting gurus, sorry if i am doing this >>>>>>:deadhorse:


lets say you nix the base gasket to get your squish and you have raised your exhaust port by the same amount the cyl has dropped....

i asume the intake timing has been altered but this drop in the intake floor is o.k. as it is just like porting the floor lower when using a base gasket?

also, what do you do with the transfers after lowering the cylinder?
do you raise the tops to recover your original timing on them?


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## blsnelling (Jan 13, 2009)

Your assumptions are all correct. If you're just starting at this, don't raise or lower anything other than setting the squish. The .018-.020 you lower the jug by removing the gasket only amounts to about 1* of port timing. It's not enough to worry about. Concentrate on port width and shape and you'll get the gains you're looking for.


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## volks-man (Jan 13, 2009)

thanks *DARTH*! 
i will not be fooling with the timing if i can help it!

out of curiousity, how many degrees difference does it take before you need to start raising and lowering ports/transfers to recover your original timing?


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## blsnelling (Jan 13, 2009)

volks-man said:


> thanks *DARTH*!
> i will not be fooling with the timing if i can help it!
> 
> out of curiousity, how many degrees difference does it take before you need to start raising and lowering ports/transfers to recover your original timing?



I don't have enough experience to answer that. I lowered the jug about .060" on my 084, but the popup was .042". That did alter the intake timing that much though. I did not have to change the factory timing at all though. I measured the timing on everything and the number were pretty good, actually a little high on the exhaust and transfers. It still has good compression though, about 170-175.


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## Bluemaxpilot (Jan 13, 2009)

You guys buying or milling out these domed pistons? If buying, then where?


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## blsnelling (Jan 13, 2009)

Bluemaxpilot said:


> You guys buying or milling out these domed pistons? If buying, then where?



Custom made on a mill/lathe.


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## Martinm210 (Jan 13, 2009)

Has anyone read through this Gordon Jennings book?

I just started in on it and there's alot of really good information there.
http://www.edj.net/2stroke/jennings/

Rather than guessing, there's some tools in there that'll let you figure things out. Not sure if I'll be successful, but I'm going to try and write a spreadsheet using the tools he's provided within, seems like it would be worthwhile.

There's some other really good stuff on muffler/pipe design which is giving me some idea to improving the internal baffle system on our mufflers. I don't think we can complete the necessary length internally for a fully tuned pipe, but I would think a short megaphone style internal baffle at the appropriate angle would help draw exhaust out of the cylinder. Again rather than simply cutting a larger hole for exhaust, maybe something additional to simulate some of the properties?

Anyhow the porting information in his book is really good and generalized as well. It goes into figuring out port area and time and some recommended values for intake/transfer/exhaust and how different shapes of ports affect the power curves, etc. Anyway, there's tons of good stuff in there. It's alot to absorb, but pretty neat.


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## lovetheoutdoors (Jan 14, 2009)

blsnelling said:


> Your assumptions are all correct. If you're just starting at this, don't raise or lower anything other than setting the squish. The .018-.020 you lower the jug by removing the gasket only amounts to about 1* of port timing. It's not enough to worry about. Concentrate on port width and shape and you'll get the gains you're looking for.



i was wondering about this myself...thanks


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## volks-man (Jan 15, 2009)

*advanced porting for dummies*

i have a few questions for the porting gurus:

upon taking this echo apart i found that the lower end of the transfers are barely open when the cylinder is on the 'case'. note in pics 1 and 2 the cylinder extends into the 'case' and the transfer is only opened by a narrow margin beneath the cylinder and by small cut in the bottom of the cylinder wall. since this area is easily accesed, is this the time to open it up?
by simply enlarging the notch at the bottom of the cyl wall? 

also, echo did not leave much meat around the ports. it would appear that the best i will be able to do is open them more or less with a large bevel. suggestions? also a ring end is nearly exposed on one side of the intake when at bdc. will opening the intake on only one side be detrimental?
lastly, i have no windows on the piston, nor much excess weight. where might i be able to seek improved flow in this situation?

btw: i am going to knock 8-9 thou off the piston for a pop up. this should leave my squish @ 20-21 thou with no base gasket. comments?
thanks guys!


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## timberwolf (Jan 16, 2009)

You need to look at where the piston is at BDC, it may be the real pinch point and cutting down the jug may disrupt flow more than it with reduce the pinch point between jug and case.

Looks like there is opportunity for smoothing and match though.


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## volks-man (Jan 16, 2009)

good point. 
though i don't think i need to cut the jug down any. (just remove gasket)

i assume you mean to put the piston back on the rod and throw the cyl back on with no gasket and see if the bottom of the piston hits the case. 

if so, i can knock a few thou off the piston skirt?

would you grind the extended cyl wall at the lower transfer to open it up?
and/or notch the bottom of the piston on the sides to improve flow to the lower transfer? 

that extended cyl wall at the transfers looks like a huge bottle neck!


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## timberwolf (Jan 16, 2009)

No, there will be no change in height between the piston and case.

Put the piston in the bore with a shim in the head the thickness of your new squish band height and see how it lines up with the bottom of the jug. From there you can decide just how much removal of material is warranted.

Also a good trick is to put some clay or playdough in the lower port, put it together cylce the piston and take an impression of the pinch point, cut a cross section in the direction of flow, that should aid in making changes to improve flow.


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## volks-man (Jan 16, 2009)

timberwolf said:


> Put the piston in the bore with a shim in the head the thickness of your new squish band height and see how it lines up with the bottom of the jug. From there you can decide just how much removal of material is warranted.



remember this is a *'for dummies thread'*. 
piston is at the top of it's stroke with simulated squish. look at the bottom of the skirt in relation to bottom of cyl. 

where am i looking to remove material? remember the piston has no windows. all of my transfers is at the base of the cylinder. 
i understand the clay pinch trick for the transfers at the base but fail to see what the mod would be.


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## volks-man (Jan 16, 2009)

sorry guys. i apologize for not knowing the terminology involved. admittadly i have much to learn. 

to try and clarify:
my observation is that *all of my intake charge *must flow through the tiny little notch at the bottom of the cylinder wall when the cyl is bolted on the clamshell. see below. a simple widening of the notch across the width of the transfers is all i propose. any warnings or downside to this?


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## Martinm210 (Jan 16, 2009)

I would get a good feeling for where the piston is setting at BTD and put the piston in there and observe the flow path through the piston window into the transfer port. If it looks like that wall is creating an obstruction, it may be a good opportunity.

I would try to simulate the same stepping they have in the stock jug and make sure the edges are nice radii so you're not introducing stress points.

Reading the Gordon Jennings book seems to indicate that transfer ports only need about 1/2 as much time/area as the intake/exhaust, so don't try to make it the same size as the intake/exhaust. Apparently that's not optimal.


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## timberwolf (Jan 16, 2009)

Yes, I forgot a step I gave you the method to locate the piston at the TDC position. You need to measure down from that position the length of the stroke.

So either put some sort of a block in the cylinder that is the height of the stroke plus the height of the squish and push the piston against that to see where the piston is at bdc, or use calipers with a depth gauge inserted down through the plug hole and zeroed to TDC then push the piston down with the depth gauge the length of the stroke to place the piston at the BDC position.


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## volks-man (Jan 16, 2009)

Martinm210 said:


> I would get a good feeling for where the piston is setting at BTD and put the piston in there and observe the flow path through the piston window into the transfer port. If it looks like that wall is creating an obstruction, it may be a good opportunity.I would try to simulate the same stepping they have in the stock jug and make sure the edges are nice radii so you're not introducing stress points.
> 
> Reading the Gordon Jennings book seems to indicate that transfer ports only need about 1/2 as much time/area as the intake/exhaust, so don't try to make it the same size as the intake/exhaust. Apparently that's not optimal.


i appreciate your comments, but,
there are no windows on the piston. all of my intake charge flows through the little notch at the bottom of the cylinder up through the transfers.
see pic below. piston in the background is entirely enclosed.


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## blsnelling (Jan 16, 2009)

It seriously looks to me like the flange of the cylinder that sticks down into the case recess would almost entirely block off the transfers. I just now realized what you're talking about. I'd be thinking of notching that out as well. I don't see what it would hurt. There's no side load there. My Stihls are wide open all the way down after a port job.


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## volks-man (Jan 16, 2009)

thanks brad!

this is exactly my concern. i had no intention of fooling with transfers but when i saw that piddly little notch i figured that can't flow well! and it is easy to access to boot!


o.k. so i'm back where i started now.  widen exhaust and intake. polish exhaust. widen the transfer notch at the bottom of the cylinder. 

start with 32 thou squish. remove 20 thou gasket. lathe 8 thou off the squish area of piston. = better flow and high compression. 

thanks again snelling and twolf!


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## blsnelling (Jan 16, 2009)

If you've got the ability, remove the .008 from the squish band of the cylinder head. If you do the piston, I'd recommend taking it down until you only have .100 of crown above the ring groove. Then mill the base of the cylinder down to set your squish. That way you maximize your compression while you're making the popup. Don't be afraid to go on down .016 on a small saw. That'w where I have my 260.


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## 056 kid (Jan 16, 2009)

I ran the 288 4 days this week. its starting to run like a raped ape now that the comp is up. i am debating weather to do the bearing/seal replacement this weekend or just run it some more. When i do, i am going to widen the transfers more and maximize the intake as well.

Has anyone done the intake on a 288 before? Did you do anything to the plastic manifold like match it up with the port? Plastic just gets so0ft and burns when you put a grinding tool to it..


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## volks-man (Jan 16, 2009)

blsnelling said:


> If you've got the ability, remove the .008 from the squish band of the cylinder head. If you do the piston, I'd recommend taking it down until you only have .100 of crown above the ring groove. Then mill the base of the cylinder down to set your squish. That way you maximize your compression while you're making the popup. Don't be afraid to go on down .016 on a small saw. That'w where I have my 260.



sadly i barely have the ability/equipment to pop the piston.  milling the squish band in the cylinder and milling the cyl base where the cyl wall protrudes, will probably not happen.

my idear to maximize compression _ was _to pop the piston with no gasket rather than use .008 gasket to set squish. 
but if i can go to .016 then maybe i will go back to using a gasket and use some paper that mic's out at .005 -.006. 
might lose a few lbs compression but will also be far simpler to do!

although, the pop-up would help maintain something near stock timing. hhhmmmm. 


thanks again guys!


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## bonden (Jan 18, 2009)

I have tryed to do a litle portin to day i got some grinding tools from my dad.


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## blsnelling (Jan 18, 2009)

You need to make sure the top and bottom are not flat. Try to make everything smooth and even too. Don't forget to put a bevel back on the port edges. What grinder are you using?


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## bonden (Jan 18, 2009)

I only changed the with of the port and some bumps in the intake and exhaust chanel , The tools i use are old dentist grindingmachine and bits.


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## super3 (Jan 18, 2009)

Last pic of the cylinder....the the bottom left corner of the port looks awfully square


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## bonden (Jan 18, 2009)

What problems wil that make i am new to this so i just grind until its perfekt ,you mean the corner should have more radius ,is this to make sure the rings dont get stuck.


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## blsnelling (Jan 18, 2009)

It's not the corner radius that is critical. What is critical is the shape of the top and bottom of the port. It they're too flat, they'll catch a ring and trash the engine.


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## volks-man (Jan 18, 2009)

*blsnelling + timberwolf + others*

thanks for all your help with my echo cs-440 port project.

work done:
widened exhaust
widened intake (one side only, ring end issue)
huge change in transfers at cyl-case intersection.
small notches added to bottom of piston at lower end transfer.
pop-up added to piston
jug lowered by .020, squish from .032 to .020
muffler opened _more_
retune by ear.

results:
immediatly i could_ hear _the compression (before i opened the muffler) you guys know what i mean... the saw has a tinnier sound idling like my stihls.
i never timed a cut before teardown. seat of the pants testing says the saw turns a fraction faster than before (will tach later). the saw absolutely, definitly, positively has *more torque*, and lots of it. you can _almost _lean on it as hard as my 361.  before the mods it was a torqueless wonder. 

i think that i need to toss the 18" bar + .325, and grab a 16" + 3/8. 
i honestly believe it will pull it now!

thanks for all your input guys!


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## blsnelling (Jan 18, 2009)

Once you run a ported saw, you're ruined forever. Congrats on a successful job.


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## volks-man (Jan 18, 2009)

blsnelling said:


> Once you run a ported saw, you're ruined forever. Congrats on a successful job.



silly question, i know, but do all saws respond like this?
night and day difference in torque! 

i really only knocked the chamfers off the exhaust and one side of intake (intake was already nearly as big as intake boot anyway). i can only figure that those transfers closed off almost completely as a way to control emmisions by way of limiting intake charge being sucked out by exhaust.....
basically the saw only got just enough fuel/air to run, but not run strong.

anyway, if all saws respond similarly, then i think i have another echo and a poulan/craftsman i can play with before i attempt work on the stihls. 
thanks again!


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## Crofter (Jan 18, 2009)

Ring expansion plus any gas pressure behind it in the ring groove is constantly trying to bulge the ring out into the unsupported opening of the port and the wider you make the ports as a percentage of bore diameter the worse the bulge.

If the top and bottom of the ports have an arch to them the ring is gradually squeezed back in from each side of the port. With no arch the ring suddenly is brought up against the whole width of the port and tends to get slapped instead of eased back into the ring groove. Sometimes if they catch the ring snaps; sometimes the ring lands of the piston get shmucked or maybe both.

That sharp corner in port in the picture not only reduces the gradual squeezing effect on the rings, but because of the unbalanced shape from one side to the other has the effect of trying to rotate the rings each time they scrape by and can hammer out the ring end locating pins.

For a given port width the more square and less round it is, the greater is the effective flow time / area, but the harder it is on the rings. Some aftermarket exhaust ports are severely squared out. A square across top is worse than on the bottom because of the relatively higher piston speed. Just a little more engineering and attention to detail would make them a much better product.


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## bonden (Jan 18, 2009)

Thank you Crofter ,this was the explaining that made me understand a lot more ,Then a know what i have to do after work to monday more grinding.


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## bonden (Jan 19, 2009)

Some more grinding i hope this is the way to go .


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## woodyman (Jan 25, 2009)

Except for smoothing and cleaning up and puting a bevel back on it looks very good,or I'm I wrong.


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## blsnelling (Jan 25, 2009)

You need to make the sides of the port straight. The way they are you're only getting maximum width, and flow, at one small point. The sooner it can get to max width, the more it will flow.


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## Martinm210 (Jan 25, 2009)

Ports are looking good. Here is a diagram from Gordon Jenning's book. Note that the intake port does not need a rounded "TOP" as the rings never pass below the top edge.

The shape of the bottom edge does help prevent the skirt of the piston from snagging though, also makes the intake sound quieter.


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## Martinm210 (Jan 25, 2009)

This is also from Gordon's book on the proper way to chamfer the edges. Notice there is slightly more rounding given by the chamfering. This helps the rings gradually contract. He also notes a small amount of rounding at the edge to improve gas flow, but I'm not sure many folks actually do that.


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## Martinm210 (Jan 25, 2009)

Finally regarding size:

These are Gordon's suggested port time area numbers:



> For piston-controlled intake ports, 0.00014 to 0.00016 sec-cm2/cm3
> For transfer ports……………….., 0.00008 to 0.00010 sec-cm2/cm3
> For exhaust ports……………….., 0.00014 to 0.00015 sec-cm2/cm3



The cm3 is just the cylinder volume.

Seconds is determined by the port duration and RPM.

But looking at the numbers you can see that you want about the same intake and exhaust, if anything slightly more intake than exhaust time area and the transfer ports are a fair amount smaller.

This does depend on the port duration though, so if the intake and exhaust durations are very different then that would have to be figured into it.

For quick and dirty area, you can use spaghetti noodles and count them up.


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## timberwolf (Jan 25, 2009)

Keep in mind those measurments are for bike sized engines, bevels on chainsaw ports will be smaller.

There is a down side to having too much bevel too, sure a round edge is better for flow, but a port that opens slowly with lots of restriction just bleads of pressure before the port fully opens and weakens the exhaust pulse.

You don't need bevel on the sides, this just widens the port from an unsupported ring width prespective without really increasing the flow capacity.


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## woodyman (Jan 25, 2009)

blsnelling said:


> You need to make the sides of the port straight. The way they are you're only getting maximum width, and flow, at one small point. The sooner it can get to max width, the more it will flow.


 Your are right as usual,but it still looks very good for not being just right.


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## Martinm210 (Jan 25, 2009)

timberwolf said:


> Keep in mind those measurments are for bike sized engines, bevels on chainsaw ports will be smaller.
> 
> There is a down side to having too much bevel too, sure a round edge is better for flow, but a port that opens slowly with lots of restriction just bleads of pressure before the port fully opens and weakens the exhaust pulse.
> 
> You don't need bevel on the sides, this just widens the port from an unsupported ring width prespective without really increasing the flow capacity.



Thanks! I've been trying to just mimic what the saw already had. .080" is pretty big, it seems like I've been seeing something more like .040-.050" for the bevel.

One thing I thought was interesting was how the port itself is pretty flat on top, but the chamfer/bevel is slightly rounded. I guess that's one way to do it.

On a side note, what is the minimum recommended piston skirt width cover recommendation. I know you want to have enough to preven the skirt from falling into the port obviously, but what's a good target 2mm?


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## parrisw (Jan 25, 2009)

Martinm210 said:


> Thanks! I've been trying to just mimic what the saw already had. .080" is pretty big, it seems like I've been seeing something more like .040-.050" for the bevel.
> 
> One thing I thought was interesting was how the port itself is pretty flat on top, but the chamfer/bevel is slightly rounded. I guess that's one way to do it.
> 
> On a side note, what is the minimum recommended piston skirt width cover recommendation. I know you want to have enough to preven the skirt from falling into the port obviously, but what's a good target 2mm?



.075" I think, that's what I went to.


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## Lakeside53 (Jan 25, 2009)

Best thing is to mimic the factory bevel. It's way smaller than 75 thou...


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## parrisw (Jan 25, 2009)

Lakeside53 said:


> Best thing is to mimic the factory bevel. It's way smaller than 75 thou...



I think he is talking about the skirt width to port edge clearance.


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## timberwolf (Jan 25, 2009)

> Best thing is to mimic the factory bevel. It's way smaller than 75 thou...



LOL, not if it's one of the ugly new Stihl 460s. Check out the side of the exhaust bttom right, it's like that all the way around the exhaust port.

Bevel is most importaint right in the center, near the sides it maters less. I like to taper starting with just a softening of the edges at the sides to likely .040 near the center of the port.


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## Erick (Jan 25, 2009)

parrisw said:


> I think he is talking about the skirt width to port edge clearance.



:agree2:


and you want at a minimum 1mm or .040 but you also don't really want to go wider than 70% of the bore dia. I like to be a bit shy of "max" and remember measure twice cut once..... or in this case measure twice cut a little and then measure twice again.


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## Martinm210 (Jan 25, 2009)

Yes, I was talking about the piston skirt coverage also.

Good stuff, so about 1-2mm or .075" for the piston skirt coverage and not more than 70% of the bore.

For the bevel around .040" in the center and less toward the sides.

Has anyone had experience with different intake bottom shapes as noted in the Gordon Jennings book like the v-bottom, etc?


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## bonden (Feb 19, 2009)

My ported saw is now up and running ,i have used it for a few days now and it is pulling strong ,the compression was 165 when cold after i put it together. Is it not posible to adjust the carb to make it ower rew ? the full speed does not increase much when adjusted.


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## timberwolf (Feb 20, 2009)

> Is it not posible to adjust the carb to make it ower rew ? the full speed does not



Hmmmm?

Does not sound right, have you removed limiter caps?

Any saw I have seen with HS and LS jets you can lean it down so it's far too lean and reving like mad. well except the saw with limited coils, when modded they are a pain to tune right.


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## mustard (May 31, 2009)

I need help modding an Echo saw with a reed valve.
Anyone out theredone any work on porting and modifiying a reed valve chainsaw.
Any other website that may be able to help??
Thanks
Greg


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## Brownpot Deaton (May 31, 2009)

if thats not a answer and get banned for life post around here, i dont know what is.


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## Evan (Jun 1, 2009)

nah im sure thats not banned for life.

thatl only happend to me over something weird im sure, i think ive been leaning that way latly, with negetive points all over the place


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## mustard (Nov 20, 2009)

Is it okay to nix the base gasket and put the cylinder directly on the case only using sealer, if that is what you need to do to get the correct squish???
Thanks


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## AUSSIE1 (Nov 20, 2009)

mustard said:


> Is it okay to nix the base gasket and put the cylinder directly on the case only using sealer, if that is what you need to do to get the correct squish???
> Thanks



Without the means to turn a cyl, this is what most do.


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## cheeves (Aug 1, 2011)

FELLNORTH said:


> Would Like The Same Info...
> Thanx For Posting


 
Me too. Cheeves


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## SierraMtns (Nov 18, 2019)

Great thread. Thanks Brad and the other guys willing to teach about porting.


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## Yotaismygame (Nov 18, 2019)

Do a google search for "porting theory". You'll find some very long threads with tons of good info. Really helped me get into porting.


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## OldMontanaPhart (Dec 17, 2020)

Sorry to revive a 13 month dormant thread, but I'm wondering if any of you porting fellas will accept a new aftermarket 034AV "big bore" jug and do a basic woods port on it and mail it back to me without breaking the bank? 

I know the heavy-hitter porting guys are booked solid several months out and want the whole powerhead to tune it to the max to demonstrate the full potential of what they can do, but I'm not really needing the full Monty here. I would not expect any sort of guarantee seeing as to how it IS aftermarket but would certainly like to have just a bit more oomphhh out there in the back 40 without sacrificing too much reliability and without adding weight [really don't want to have to drop down to the 009 weight class just yet despite pushing 70...].

I will use new OEM circlips on the pin, do a decent breakin with a fairly rich mix for the first 3 or so tanks and not badmouth anyone even if it blew up on the first start since there would be so many variables in the mix [aftermarket p&c/rookie saw mechanic here/saw with ancient bottom end, etc].

How about it? Any takers?

Ran a 20" bar on this thing for 25+ yrs and just put a 24" on it [durn trees musta grown some-needed to cut several 18-20" Doug firs and a 20" 3-stem pine that were starting to threaten the house...]. 

While it did this job well, I would love to have that extra grunt with the 24" to turn those butts into firewood.

Saw has had one new air filter and one new recoil starter, the usual plug, clutch and b/c replacements. Also had to replace lost dogs once. Never have replaced fuel or impulse lines. I've never even retightened the cylinder bolts. Amazingly enough, it is still on the original brake band! Has heated my house unfailingly for all those years, and I got it from my Dad after he had used it for several years.

I even abused it unknowingly by using outboard 2-cycle oil for a number of years, although I have always mixed closer to 40:1 than 50:1. Also used to run it bone-dry before refueling sometimes. Ignorance is bliss, they say-


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## Yotaismygame (Dec 17, 2020)

Problem with the AM jugs is the plating likes to flake off. I've ground Hwy cylinders before that had that issue. Did a 288xp meteor cylinder once though that had no issues. It's a gamble for anyone to grind on one is what I'm getting at. Ask around for a OEM cylinder. I just sold a 036 jug last week..


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