026 compression

[Car-guy2]

Picked up an 026 that wouldn't run unless you primed it. Checked the usual: fuel lines, carb., choke. Finally checked compression and it was 90 psi. Tore the saw down and ring gap was huge and piston skirt worn.
I bought a meteor piston with caber rings. Polished the cylinder with scotch brite pad and checked new ring in cylinder. End gap was .008. Set squish at .023. Saw starts and runs well after tuning. Put a tank of gas through it and checked compression. It's only 130 psi. Checked a couple other saws cause I suspected gauge was bad. My old 041 that runs great showed 90 psi. I thought "OK gauge is bad". Then I checked my 024 that I got used and have cut with for 4 years and it pulled 150.
So today I got another gauge and 026 checked 130 cold and 120 hot.

Is this saw gonna get better with use? And how can my 041 run so well with only 90 psi? Both gauges are older, could I have gotten 2 gauges that are off by the same amount?
I've gotten a ton of useful info on this site. Thanks in advance for any insight on this.

 

[timbercare366]

I'm kinda in the same boat here, have 7 saws and its kind of a hit and miss. Only 2 have great compression readings and 4 others that seem to run good for some reason have compression readings between 100-130.

 

[Car-guy2]

I expected 150 or better with new piston kit and squish at .023". I guess I should try another gauge. Weird thing is my 024 that I figured to be about worn out is pushing 150 on this same gauge

 

[tickhound93]

The "minimum" compression for a 2 stroke to run is 90 psi. If you put new rings on and you got 130, run it. Anyone who says a saw absolutely needs 150 psi or higher to run is full of condensed owl ****. Most of the time. Some engines are very picky though and like high compression. If it runs good I wouldn't worry about it.

 

[timbercare366]

I am wondering if the gaskets and membranes are worn to a point its causing a vacuum leak, I have had this problem before with a different saw some time ago but the saw certainly didn't run that well before I fixed it. The only thing about fixing these small engines is its all ruling out the non related problems and pretty much guess work

 

[a. palmer jr.]

Same here, just run it. The cylinder probably has a little bit of wear and the rings aren't seated in yet so the magic 150 may not be attainable. I don't think the piston port engines do well at the lower compression whereas the reed valve engines can run with compression lower.

 

[timbercare366]

Sometimes it is just simple as a piston ring, a client I have couldn't get his little green poulan to start and he took it to the shop one day and came back and said you can have this saw its goin to cost me 150 to fix, labeled low compression, so I took it and it had a reading below 90 when I tested it so inspected it further and paid 3 dollars for the piston ring and the saw is up and running still today

 

[John Lyngdal]

My 026 pawnshop find had a compression of 130, but the piston skirt was clean and the cylinder wall was fine. Squish was .037" So I ordered a replacement Meteor piston with Caber rings. Got ham handed and broke one of the rings tonight when installing the lower ring. I just consider it a $15 lesson to be more careful next time. While I'm waiting for the new ring set to arrive I decided to check the squish with the new piston and compression even with just the single ring. Squish with the Meteor piston was down to .017", so the cylinder gasket will be staying where it is. Compression was all the way up to 200 psi. I run ethanol free premium and Amsoil Sabre at 40:1 so I'm not expecting any high compression issues even after the rings have have worn in. Then again I could run 110 octane leaded racing gas.......<LOL>

 

[Ax-man]

I wouldn't worry about either. I used to be one of those guys who thought 150 lbs. was the magic number for compression on a saw. Not any more, Example, I completely redid an 056 Super years ago. It had over 150 lbs. when finished. I went to do some routine service on it and found the air filter some how got bad and could have been letting dirt and other nasties go directly into the engine. Redid a comp check and was down to 130 lbs. I thought owe s### I ruined the saw . Nope , still runs the way it always did after I fixed the air filter problem and it is still strong to this day. Still hard to pull over till it starts but these saws have an adjustable timing and that might be a smidge off . I dunno know . If it ain't broke I am not going to fix it.

I am going to throw this out and see what happens. Anyone ever see an actual official compression reading for a Sthil saw??? I haven't. To my knowledge through reading and internet browsing Sthil doesn't put these numbers out because they are irrelevant, primary compression or bottom dead center is what they Sthil determines is a better indication how good a saw will perform, top dead center is considered secondary compression which is why you won't see any compression numbers for a Sthil saw. I hope I am explaining this right. I have no clue hoe to check primary compression except to do a pressure /vac test with the piston at BDC verses TDC. This is just a tid bit of info I have picked-up on and just passing along . Might start a fight but who cares . Right, as long as the saw works good and flies through that wood with the greatest of ease is what is important no matter what a comp gauge says

 

[a. palmer jr.]

I think the kind of engine it is has a lot to do with it. I have a Lawn Boy 2 stroke lawnmower that has had 90 compression for several years and is still running fine except is kinda hard to start when hot. It has reed valves as opposed to the Stihl piston ported arrangement which I feel makes a big difference because of the primary compression as you mentioned.