026 arguing with me.

[Wood Doctor]

I’m sure the decomp was closed, I even tested it right after the engine ran. I did also test the valve with soapy water for a leak and no bubbles. I am going to try to find someone to borrow a tester from to be sure.
Thanks for the reply!

Some operators here have thought that the decomp is closed when pushed in. It's a very simple error to make. With my compression tester, I have never measured a compression reading as low as 40 psi on any chainsaw engine.

 

[DERaffle]

Some operators here have thought that the decomp is closed when pushed in. It's a very simple error to make. With my compression tester, I have never measured a compression reading as low as 40 psi on any chainsaw engine.

It was definitely closed (out). I even removed it, cleaned it and reinstalled. Tested with soapy water.
Driving me nuts.
Having fun working on it thought. Just wish I could make some progress.

 

[DERaffle]

I've rebuilt a bunch of 024/026 saws and they're super easy to work on as long as you have a T27 long driver and 8mm spin tight driver.
If it fires and runs with fuel down the carburetor throat then dies out, the compression is still marginal to good, but something in the fuel delivery system is the issue.
This includes fuel lines, crankshaft seals, carburetor cylinder boot, plugged fuel filters, leaking fuel lines, an ethanol damaged metering diaphragm, or one or both debris clogged jets.
If you have good spark and you can't get the saw to run briefly with fuel down the carburetor throat chances are the compression is the issue.
If the fuel down the throat starts the engine and it continues to run and revs then stumbles open the High jet ( one closest to the airfilter) a 1/4 turn and repeat.
If it still doesn't run, run the adjustments all the way in then back out to the original position and try starting it again.
If it still doesn't run back out the High jet another 1/4 turn and try to start it again.
If it doesn't run properly pull the carburetor and check the fuel filter screen and metering diaphragm.
If those look good, swap in a different carburetor.
If that doesn't work check the fuel line, fuel filter, impulse line, and carburetor cylinder boot for defects.
The last easy thing do check the torque on the mounting bolts and tighten as needed, if those are normal pull the cylinder and check the piston and cylinder bore for scoring, and also check is the cylinder gasket.
If all these look good, time do a vacuum test or just replace the crank shaft seals.

How involved is replacing the seals? Will I need any special tools?

 

[pioneerguy600]

You need to remove the flywheel, make a screwdriver to pop the seals and a couple deep sockets to drive them in straight and proper. It would be much easier to have a pressure and vac test performed first to see if it is a air leak or no.

 

[John Lyngdal]

I set my digital camera into 1024 x 768 "PC" mode if I'm going to insert them into the post, but use ~3Mb pictures if I'm leaving them as a thumbnail attachment.
Pictures of the top of the piston and the skirts on the intake and exhaust side of the piston would be most useful to start.
Scored pistons are pretty obvious, so I hope the low compression reading has something to do with your instrument.

 

[DERaffle]

 

[John Lyngdal]

I don't see an issue in those pictures. The expensive parts are functional, now to work through the list to find the issue causing the starting and running problems.
Since you have already tried a carb swap without success I'd remove the AV retaining screws and separate the fuel tank and handle from the crankcase to check the fuel and impulse lines along with the carburetor boot for cracks or damage.

 

[DERaffle]

I don't see an issue in those pictures. The expensive parts are functional, now to work through the list to find the issue causing the starting and running problems.
Since you have already tried a carb swap without success I'd remove the AV retaining screws and separate the fuel tank and handle from the crankcase to check the fuel and impulse lines along with the carburetor boot for cracks or damage.

I did replace the impulse and fuel line and have a boot coming soon, all OEM.
Is it worth the price for Stihl rings?
Thanks!

 

[John Lyngdal]

I use Caber rings in my rebuilds and haven't had any issues.

 

[gmctyphoon]

Can you show a picture of the exhaust side of the piston?

 

[DERaffle]

Can you show a picture of the exhaust side of the piston?

 

[pioneerguy600]

I agree also, there doesn`t appear to be any damage to the cylinder or piston to cause abnormally low compression, I wouldn`t trust that compression tester either. I have built more tha 25 of these saws likely closer to double that repaired and running strong. Have never seen compression below 100 on even a scored up P&C saw.

 

[DERaffle]

I agree also, there doesn`t appear to be any damage to the cylinder or piston to cause abnormally low compression, I wouldn`t trust that compression tester either. I have built more tha 25 of these saws likely closer to double that repaired and running strong. Have never seen compression below 100 on even a scored up P&C saw.

Since it’s already apart, do you think I should change the rings?

 

[Duane(Pa)]

Since it’s already apart, do you think I should change the rings?

Yes. No reason not to at this point.

 

[Duane(Pa)]

The choke flap is notorious for causing trouble on this model. Put the choke lever in the choke position and examine every aspect of the function. Lever shaft wear, lever shaft pivot bearing in tank plastic, inadequate travel of either nub that closes the choke flap, etc. Definitely the Achilles’ heel of this model!

 

[pioneerguy600]

Since it’s already apart, do you think I should change the rings?

Yes, the Caber rings are quite reasonable and your piston shows it has a lot of hours of run time on it. Clean the cylinder up with Scotchbrite to remove all glaze and a new set of rings will boost comp by at least 20 lbs, likely more over a worn set. We check ring end gap with feeler gauges to tell actual ring wear but in your case just replace them. Was thinking of Meteor pistons, they come with Caber rings, changed as clarification.

 

[DERaffle]

Yes, the Meteor rings are quite reasonable and your piston shows it has a lot of hours of run time on it. Clean the cylinder up with Scotchbrite to remove all glaze and a new set of rings will boost comp by at least 20 lbs, likely more over a worn set. We check ring end gap with feeler gauges to tell actual ring wear but in your case just replace them.

I was wondering what you would expect the end gap to be on a good set of rings. I am definitely going to replace them but was just wondering.

thanks for the input!

 

[pioneerguy600]

ring gap of .005 - .006 would be new, worn out by the time it gets to .020 but I replace them any time they are over.016. I only use OEM rings myself but the Caber rings get a huge endorsement from this forum.

 

[DERaffle]

ring gap of .005 - .006 would be new, worn out by the time it gets to .020 but I replace them any time they are over.016. I only use OEM rings myself but the Caber rings get a huge endorsement from this forum.

I do plan on using the OEM rings but none of the local dealers have them in stock. Would you have a part number?Is there a good online source?

 

[irhunter]

If I were you, I would Google around some...you can find both the Stihl shop manual (with things like ring gap specs) and the Illustrated Parts List (with PNs) for the 026. All for free.

If you phone dealers up, they will mail you parts. And, some outfits like Bailey's have a limited selection of OEM. But, the "Stihl deal" is that there are no comprehensive on-line OEM parts sources.