Redneck cylinder milling?

[eyeinstine]

Okay, here's one for you's.. I may be from 'jersey, but i can still be a hick... I'm messing with a old Dolmar 100 i pickde up on ebay for 21$ with shipping.. Decent shape, no spark and missing air filter cover.. Piston and cylinder look like new.. I got a new ring on its way just start fresh. I wanted to experiment with this saw, and hopefully make a powerful light weight saw for small firewood and occasional limbing.. i know i could let one of the pro's here do it, but it is just more of a fun thing.. If i screw it up, i wont loose much sleep (or money) or it..

I am thinking of trying to bump the compresssion up a tad.. I've searched the threads, and am reading many pro's and con's to it. Lower the cylinder only without changing ports changes the port timing. It suposedly moves the peak power a bit lower..

Is it safe to assume, with the higher compression, it will still make more peak HP, but just at a slightly lower RPM?? If so, then why not get the extra power, and step up one size on the rim sprocket to compensate and raise the chain speed??

I plan or either using the LOC TITE flange gasket maker and no base gasket as some have suggested.. Others say it will leak..?? Or... okay,,,, ready! heres the hick part:

Get some heavy grit sand paper, lay it on a thick piece of thick flat glass, and mill away; checking the progress at all 4 sides of the base with the micrometer making sure it is going down evenly all around.. and use the base gasket.

I plan on removing about .010 or so.. Depending on how the 'milling' goes.


Okay, the flame suit is on.. let me have it...
Ron

 

[chainsawworld]

ron,
i don't think i would do that on the smaller saw. not so much your methods but dropping the jug. my suggestion is to change your port timing and open the muffler. marty

 

[TonyM]

I think I'd try it without the gasket first, just using the sealant. I don't think you would notice much of a change in performance anyway, without a corresponding change to the port timing. It certainly will last long enough for you to try it. It would be easy to try both different ways and see if you notice a change in power. I think you could mill the base as you describe, but a granite surface plate would be a lot nicer to work on, and keeping the base flat and perpindicular to the bore will be critical.

 

[ehp]

Sure the way you said you wanted to lower your jug will work, as long as this jug is flat on the bottum, I have not worked on this saw you have so I donot know but if it is like a husky or 7900 jug it would be pretty tricky to keep it straight because the bottum of the jug fits into the crankcase . I use loc-tite 515 and never had any trouble on leaks.
Now how are you going to lower your jug without changing your ext. and transfer port timing, if you lower your jug .030 , your are lowering the ext. and transfer ports .030 because your piston has not changed , you should measure your squish before you go start playing to make sure you donot end up with your piston hitting the top of your jug, have fun

 

[eyeinstine]

ron,
i don't think i would do that on the smaller saw. not so much your methods but dropping the jug. my suggestion is to change your port timing and open the muffler. marty

Marty,

Thanks for the input.. Why do you say not to do it on smaller saws??? I was thinking that adding a little more grunt down lower, and possible a little wider torque curve, would be a help.. Though i'm sure if that was the case, the saws would just be made that why.. But hey, i'm having fun dreaming...
These small saaws seem to have a small range of power, and you have to kinda concentrate to keep the RPMS just right as your sawing. Im looking for more grunt where i can just drop the saw and let it dig in. If the power is there, maybe up the sprocket and run a 12" bar as opposed to the 14".

Port timing.. Hmmmm... I would really like to mess with that too; but dont know where to start... I worked on V8 race motors for years, but this is all new! And all my tools are a bit oversized for the Job!

Muffler mods...
This saw has a WACKY muffler.. It is an early dolmar 100, and the current parts list doesnt even show this muffler. It is a 2 piece cast aluminum muffler.. The exhuast exits the port and is directed downward into a large resevoir area in the muffler.. Then at the side of the muffler, there is an opening; and the exhuast travels through a sealed up channel, or passage, and works around the perimeter of the muffler housing, until getting to the other side, where is is directed out a rectangular opening and released. I cant figure out if this is a good design or or bad??? I wonder if the exhuast traveling this 'hallway' has the same effect as having a pipe??? Why did dolmar drop this muffler so quickly?? Too costly?? A stamped sheetmetal muffler has to be a big cost savings over a technical cast aluminum one. Or did they drop it because it didnt work?? Should i cut and grind it up?? Or is it a museam piece!

Ron

 

[eyeinstine]

I think I'd try it without the gasket first, just using the sealant. I don't think you would notice much of a change in performance anyway, without a corresponding change to the port timing. It certainly will last long enough for you to try it. It would be easy to try both different ways and see if you notice a change in power. I think you could mill the base as you describe, but a granite surface plate would be a lot nicer to work on, and keeping the base flat and perpindicular to the bore will be critical.

Tony, i think i may just run down this lok tite stuff and give it a shot.. If i do, then i dont see a need to mill the bottom of the jug... If the gasket was a must, then the only choice would have been the redneck milling..

Thanks again!
Ron

 

[eyeinstine]

Sure the way you said you wanted to lower your jug will work, as long as this jug is flat on the bottum, I have not worked on this saw you have so I donot know but if it is like a husky or 7900 jug it would be pretty tricky to keep it straight because the bottum of the jug fits into the crankcase . I use loc-tite 515 and never had any trouble on leaks.
Now how are you going to lower your jug without changing your ext. and transfer port timing, if you lower your jug .030 , your are lowering the ext. and transfer ports .030 because your piston has not changed , you should measure your squish before you go start playing to make sure you donot end up with your piston hitting the top of your jug, have fun

Hi Ed!
Thanks for the response.. I was hoping you would chime in, but really didnt expect you to bother using your experience on a thread like this.. I'm glad you did! Since i surely didnt have the ballza to ask you these questions.

I think i will try the loc tite route.. Is it 515 or 518?? I believe another thread said 518.. I just dont want to order the wrong stuff, as i'm sure no one will have it in stock around here..

Anyone know approx thickness of a crushed stock gasket?? I assume it will vary depending on saw and maker, but there must be a common range?? Just curious how much this loc tite idea is going to lower the jug?? I may still mill a bit off teh bottom of the jug, just to get the dumb idea out of my system! Actually, i layed a straight end on the bottom of the jug, and it appears it needs to be trued up anyway. VERY slight downward slope out at the ends where the screws hold the jug down.. It doesnt look like this saw has ever been apart, so i dont htink they where over tightened.. I'm talking .001-.002... Just enouhg that i can see light under the flat edge..

Ed, this jug is flat on the bottom, and the case is flat too.. I guess it just relies on the 4 jug screws to align it properly.. But i really didnt look that close at that.. I know the jug is flat, and being a small CC saw, theres not alot of meat to mill away.. Im sure if needed, the redneck sandpaper milling would work pretty well.. Esp using a mic and making sure it is equal all the way around..

One question for you Ed, since your on this thread now.
What is your prediction, as to what will happen, if i drop this jug a bit with loc-tite and/or milling, say .010.
No changes in the ports. Will it make any more HP anywhere in the rpm range? Will i have a chance in hell of meating my goal. Making a bit more HP, at a slightly lower RPM, and slightly increase the power range?? Possible allowing me to jump up one tooth on the sprocket..
Or is this just all a pipe dream! :angel:

But hey, it is just for fun... and to learn a bit more... It all that i will lose is the jug if i want to revert back to stock..

Thanks, and i enjoy the conversation.. Positive and negative alike.. So let me have it...

Ron

 

[begleytree]

I've heard of milling .010 off the bottom of the jug to raise compression, and doming the edge of the piston to put the port timing back where it should be.
But I never did it myself, just throwing it out there.
-Ralph

 

[woodshop]

eye... if your serious about milling the thing, I do have a Grizzly entry level metal milling machine I use mostly for woodworking, but I have milled metal with it. Clamp it to the table, put an end mill in and we could shave off as much or as little as you want. I would rather see you do it that way than the sandpaper and glass deal. Not sure with the glass you could really keep it strait and level enough. I'm about an hour or so drive from you, let me know if you're interested.
Dave

 

[lucky]

Very generous, Woodshop.... That would be a better option than sanding. I think the sandpaper method might get old real quick. .010 doesn't sound like much but when you get after it with some 120 grit, you'll be surprised how long it might take. The mill would also be more accurate. A lathe also works well.

Doming the piston is an interesting idea however, removing material from the crown will lower your compression possibly negating the gain from milling. Do some reading on squish bands before you tackle this project. You'll find the info informative and will have some understanding and confidence.

Lowering the barrel will move the powerband down, by how much I do not know. It's dremel time!
John

 

[Al Smith]

Well,it's your call on the comp. ratio thing.If my info is correct,that is only a 2 cu in saw,and 2.6 hp.For what it's worth,and my opinion,you could do more with the exhaust.It takes fuel to make power.The mixture can't get in,if it can't get out.I am not familiar with the saw,but a simple thing like taking the screen off the muffler can make a world of difference regarding power.Port timing,comp ratio,etc.,is one thing,but if it can't breathe,all is for naught.

 

[chainsawworld]

ron,
that is what has been hande down to me from other saw builders. i do not think it is fair to them for me to discuss their secrets. i know their ideas work well. the sachs 100 is only 2.0 cubes. try the more forgiving things first. if you like the outcome, stop there. once you drop the deck you have to live with it or replace it. what if you take too much and the piston hits the spark plug? is a new jug still avilable? just some things to think about. marty

 

[ehp]

Hi 518 will work but I use 515 because alcohol doesnot eat it , most gaskets are in the .020 area some more some less but .020 is pretty close to normal. Pull your base gasket out, and dome you piston the same amount as the thickness of the gasket, just bevel the top edge of your piston to gain back the port timing , now you should raise the top of the intake port the same amount so your piston skirt when at TDC is inline with the top of the intake port but I think I would leave that alone for now , the biggest thing you have to worry about is heat, and I donot know this saw or I could help more so do this and you should be pretty safe, and muffler mod it , figure out your ext port area and go up to 85% of that opening in your muffler, this will give you alot more power and more torque, go for it you will be surprized at the out come

 

[eyeinstine]

Ed,

thanks for the follow up... I just got back from picking up the loc tite.. they actually had the 518 in stick, and since i dont plan on running alky in it, it should do.

When i dome the piston, should this be done all the way around, or just in the area of the ports?? How critical is the doming process.. A flat file and then smooth it out with emery cloth, or am i being a hick again!?? Should the finished product be smooth and rounded, or just a 45 degree bevel??

i do have a metal lathe, and thought of pulling the piston and cutting the bevel that way.. But if its not that critical or needed, then why do all that extra work.? Also, i would be afraid of distorting the piston or marring the surface with the jaws of the lathe..


Hey Dave (woodshop),
thanks for the offer.. Since i picked up the loctite, i dont need to mill the cyl. this way, if things dont work out, i can just put a gasket back in.. If i dome the piston, then i'll only be out the piston...

Thanks guys!
Ron

ps. I bought the bigger tube of the loc tite.. If this works out, i'll need enough to hack up all the saws.
Well, maybe not hte 61 husky.. I'd be afraid of screwing that one up...

 

[Molecule]

Although I'm not qualified to offer experience on this thread, I have been wondering the same thing and in my research and thought I might contribute this picture on piston shaving from A Graham Bell's book on 2-stroke Performance Tuning ...

He made two comments ... increases in compression can reach the point where they just result in more heat, with very little marginal increase in power, and the above, which he mentions as suitable for experiments during a tuning process. (It does occur to me that shaving down the piston may also significantly decrease compression, with the result being that one gain may produce another loss.)

I can confirm that his method of measuring squish band clearance, by squeezing the tail (maybe 3/16 to 1/4" long) of short piece (maybe 2-3") of soft 1.3mm solder definitely works, and would recommend making that measurement especially at the edges of the cylinder wall (as opposed to at the interior edge of the squish band just across from the spark plug opening, near the center of the cylinder) as a little 540 I measured got down to less than 0.5mm clearance at the edges.

 

[Stihl Crazy]

I took a stock 026,removed gasket,turned down the edge of piston .025, opened muffler,and put on lighter flywheel. Timed three cuts in 9x9 pine; 7.3 sec. Beat a stock 361,254,and Walkerized 346. Can't compete with saws by pro builders but pretty good for an old logger. I run the saw every day logging and have seen no sign of heat. Play with your saw, you may suprise yourself,I did.

 

[ehp]

If you pull your base gasket out and donot dome the outside of your piston you are changing your port timing. Not sure on the stroke or your saw but we will use 32 mm stroke just to show the difference, with 32mm stroke and you pull the gasket without doming the piston you are changing the ext. and transfer port timing by almost 3 degrees, now on the ext port that is not as important but 3 degrees to the transfer ports is on some motors very important,
just dome the outside of the piston by file or lathe what ever and I would go all the way around the outside but you donot have to go very far in on the piston because with only .020 you are not going to hit the jug with the top of the piston

 

[eyeinstine]

Molecule,

Good info and thanks for posting that diagram. Thats shows what i was asking a few posts back. Whether to cut material from all teh way around the piston, or just from the area around a certain port opening.. But i think i will do as Ed says and go all the way around.. I think by cutting only one area of the piston, wouldnt the combustion pressures act like a wedge when it gets down into the cut area and push the piston sidways.. Im sure its not a major concern, esp for a race motor, but on a working saw, i think it may have an effect on the longevity of the motor.?

Stihlcrazy,
sounds like a plan! I'll be doing pretty much the same thing, except no lightweight flywheel. I think on a small CC saw like this, the flywheel inertia will be helpful.

Ed,
I really appreciate you sharing these tips.. I'm sure being in the business of hopping up saws, it must be awkward to share some performance tips.. But I/we know theres much more to performance saw building than what we are discussing. this is just a good thread with some smart, down to earth guys tinkerin with some saws. Thanks!

I think i will pull the piston and put a few wraps of tape around it, and chuck it in the lathe so i can make a precise cut on it. I'll use a mic and check the thicknes of the current used base gasket, and then remove that thickness from the edge of the piston at a 45 degree inward cut all the way around. I'll try and get some pics of it all just for the hell of it. I've been considering putting it back together stock so i could get a baseline compression and performance on it since i have never ran it. But chances are i wouldnt find the time or the ambition to tear it back down. Also, i havent located a ign coil for it yet, so i still aint got the spark problem taken care of yet.. Hoping to find a used one since the new one is around 60$ and this is just a tinkerin' project.

thanks again,
Ron

 

[rb_in_va]

Clamp it to the table, put an end mill in and we could shave off as much or as little as you want. I would rather see you do it that way than the sandpaper and glass deal. Not sure with the glass you could really keep it strait and level enough.

woodshop,
Have you ever used a fly cutter? They work really well for light cuts over a wide surface. How do you dial in the milling head on that machine? When truing up surfaces with sandpaper I have always used a granite surface plate like this: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=12581&item=3878859807&rd=1

I think it would take a lot of time to remove .010, and do it accurately.

 

[rb_in_va]

I think i will pull the piston and put a few wraps of tape around it, and chuck it in the lathe so i can make a precise cut on it.

What kind of lathe do you have? How about a pic? Later, Roger.