026 squish, learned hard way

[AlextheUKOD]

Hey all, just figured I'd share a little bit of recently acquired knowledge. I currently have 2 stihl 026's, both with gasket delete, muffler mods. One is a black lever with shaved cylinder and a hyway piston (44mm), no porting other than a little bit of lower transfer smoothing. Other is a red lever with some mild porting and a meteor piston (also 44mm). had previously done porting and gasket delete on red lever, was running good but oem piston/rings were getting heavily worn (both saws had a lot of hard hours before i aquired) so i recently put in the meteor piston and didnt check squish for 1st couple days of running. Ran fine but when i did check clearance was at 0.009". piston was just kissing the top of cylinder- actually cut a half moon into top of piston and boogered squish band in cylinder a little. Made a .004" gasket out of pop can. With motoseal came out to 0.0143" and now have no issues saw runs great. Lucky didnt bomb the saw. Black handle is at ~0.016" and runs good too, btw.
Takeaway: Minimum squish is somewhere just north of 0.009", so don't do like I did.
This site has given me a lot of knowledge, figured I'd share some of mine.

 

[ZeroJunk]

I don't modify saws, cause I don't know how if no other reason. But, I have had vintage saws where the cylinder gasket could not be salvaged and had to make one out of whatever. Brass shim stock worked for me.
Fifteen thousandths seems to be a good minimum.

 

[sean donato]

Minimum safe squish is a much deliberated topic. I personally won't take one much bellow .020". I've torn down much higher performance engines that were slightly tighter, but never seen one purposefully taken below .015". You should consider you're self lucky you didn't take out a rod or rod bearing.

 

[82F100SWB]

My ported 026 has been at .0165 for years. It is one of the ones that had negative clearance with a base gasket delete. Did the old sandpaper glued to the piston band cut and let it eat. Never had an issue with it, but I have had a clone 660 contact at .020.... YMMV I guess.

 

[Lightning Performance]

Minimum safe squish is a much deliberated topic. I personally won't take one much bellow .020". I've torn down much higher performance engines that were slightly tighter, but never seen one purposefully taken below .015". You should consider you're self lucky you didn't take out a rod or rod bearing.

I run a 362 at 0.014

 

[sliceoflife]

Did the old sandpaper glued to the piston band cut and let it eat

English translation, please?

 

[82F100SWB]

English translation, please?

Glue sandpaper to the face of the piston, put the piston in the jug, lubricate, spin piston with drill press, cutting the band. That way the band shape matches the domed piston, and I got it done, this was before my days of having a lathe.

 

[sean donato]

I run a 362 at 0.014

I wouldn't, and wouldn't ever reccomend it. Seen too many pistons with squish band marks on them from guys running too tight tolerances. Problem just compounds with bad tunes, over heating etc. Not worth the minimal power gains to keep a reasonable safty margin.

 

[Lightning Performance]

I wouldn't, and wouldn't ever reccomend it. Seen too many pistons with squish band marks on them from guys running too tight tolerances. Problem just compounds with bad tunes, over heating etc. Not worth the minimal power gains to keep a reasonable safty margin.

Well I don't agree at all because it's my saw and it's tuned with a screw. This is a 362 first version. It has no slap and no carbon marks. If you knew how to setup a quench area to be self cleaning and acually warm up the jug before you work it this will never be an issue. I don't get temperatures below 20° much either. My stuff is set at 70°F. These are all factors you might not understand.
Is it close, you can bet your last buck, it is at times. Will it ever hit, not likely after six or seven years set there. If you knew why and how it is set like that you might understand the reasoning. Tools that leave my bench are never set this tight because I don't expect the masses to need it. Extra power is everywhere if you know where to look. Mostly reserved for racing environments with tight squish under normal calculated levels.

Edit:
So how do you calculate the number your looking to set this saw at?
I'd like to hear your reasoning in how you mathematical arrive at said number or do you follow the masses?
Let's see you spec sheet for your last engine you build, please.

Just a side note most of my work tools wouldn't pass the average guys "tolerances" in many places withing the engine. I see lots of sloppy work constantly like not checking bore and piston sizes among other things grossly overlooked.

 

[sean donato]

Well I don't agree at all because it's my saw and it's tuned with a screw. This is a 362 first version. It has no slap and no carbon marks. If you knew how to setup a quench area to be self cleaning and acually warm up the jug before you work it this will never be an issue. I don't get temperatures below 20° much either. My stuff is set at 70°F. These are all factors you might not understand.
Is it close, you can bet your last buck, it is at times. Will it ever hit, not likely after six or seven years set there. If you knew why and how it is set like that you might understand the reasoning. Tools that leave my bench are never set this tight because I don't expect the masses to need it. Extra power is everywhere if you know where to look. Mostly reserved for racing environments with tight squish under normal calculated levels.

Edit:
So how do you calculate the number your looking to set this saw at?
I'd like to hear your reasoning in how you mathematical arrive at said number or do you follow the masses?
Let's see you spec sheet for your last engine you build, please.

Just a side note most of my work tools wouldn't pass the average guys "tolerances" in many places withing the engine. I see lots of sloppy work constantly like not checking bore and piston sizes among other things grossly overlooked.

So you won't run a customers saw that tight but you'll come on here and belittle the advice I've given to an average guy that doesn't have the tools nessisary to alter the quench area or any other machine work for that matter. Thats rich, especially coming from you of all people.

 

[Lightning Performance]

So you won't run a customers saw that tight but you'll come on here and belittle the advice I've given to an average guy that doesn't have the tools nessisary to alter the quench area or any other machine work for that matter. Thats rich, especially coming from you of all people.

He has several ways to alter it. Maybe you should figure that out first before you jump on me.
I didn't say it wasn't good for the little guy. I do recommend running things tighter than most people will based on exstensive test over many years. If others so choose to follow that is on them. The fact that your pissed doesn't bother me in the least and clearly you avoided the questions I asked about your builds.
Now who is doing what?
Let us assume you don't check anything beside the almighty squish band. Is that a fair assumption?

Would you like to continue?

I'm not backing down from anyone who decides that I've given out bad advice anymore. Go get back in-line and follow the heard. It's much safer there.

Running 0.016 or 0.015 on anything with a bore that small isn't going to interfere at all with gasoline on an average tuneup. This tool was set @0.012 for testing apparently that was enough so adding two just lost power. It's just a gasket change and many don't realize in reality on the compressed cheap gasket they might be that tight. 0.020 is too much gap on a tiny bore like that. You missed one important factor your probably not even setting correctly. You give away power when you don't have to. Try it sometime.
But first learn how to setup a proper squish band profile so you know what is acually going on in there. Figure it out if your serious about learning anything. If not don't cry to me about bad advice you don't understand. Please explain to us how you go about setting up a prop quench area beyond using the common bore to ratio of area measurement. Whole lot more to it than that.
I'll be here.