Holy end gap---.060" on 026 Stihl

[atlarge54]

I'm playing with some old "tree service" Sthils to get me through the dull winter months. Yesterday I stopped at the local small engine shop and was pleased to find he had a carb kit in stock for the 026 that I can't seem to get running quite right. Today I tore in a bit deeper and the saw seemed to hold a vacuum ok. Compression was never great but not terrible either. When I pulled off the cyl and removed the top ring to check end gap and found it to be approx .060" which to me is huge.

I thought I'd try my luck and see if the local shop had any rings in stock----no such luck. The guy told me that gap is just fine. To me that seems awfully loose even if there are two rings. The piston measures approx. 1.725" and the cyl approx. 1.735". The piston isn't perfect but it wouldn't scare me to put it back in and run it.

 

[Fred482]

I checked the service manual for specs on the piston rings, couldn't find a clearance listed. It says, "check the piston rings". Ok, for what and how much?

The automotive "rule of thumb" is .004 per inch of bore size. Not sure how that applies to small engines. I would think somebody with lots of experience will chime in with the correct info soon.....

 

[blsnelling]

That's HUGE! With .060" of endgap, you should be able to actually see how badly they're worn out. They'll be worn "thin".

 

[Hedgerow]

That's HUGE! With .060" of endgap, you should be able to actually see how badly they're worn out. They'll be worn "thin".

The piston skirt will be well worn too... Replace em' both... They're cheap...
I'm thinking end gap should be in the 8 to 10 thousandths range...

 

[woodyman]

The piston skirt will be well worn too... Replace em' both... They're cheap...
I'm thinking end gap should be in the 8 to 10 thousandths range...

You are right.An end gap of .060 is HUGE.If no dirt got in the engine then you got your moneys worth out of that saw because it must have a zillion hours on it.I would get a piston and rings to.

 

[Fish]

No worries!!! Stihl's quality is so high, and the piston clearance/tolerences are so close, that their saws don't really need rings.........

 

[atlarge54]

While cleaning up the cylinder I found some grooves that are deep enough to cause it to be scrapped. The grooves run from the top of the cylinder to the upper transfers on both sides.

I've got a P/C from another one and the piston measures a full .005" larger at the skirt.

On the better cylinder the top fin is broken off from the decomp hole forward. Would it be safe to run with that small amount of fin missing?

 

[Hedgerow]

While cleaning up the cylinder I found some grooves that are deep enough to cause it to be scrapped. The grooves run from the top of the cylinder to the upper transfers on both sides.

I've got a P/C from another one and the piston measures a full .005" larger at the skirt.

On the better cylinder the top fin is broken off from the decomp hole forward. Would it be safe to run with that small amount of fin missing?

Yes...