Shiny piston= worn piston. Should have lines running across piston.
Stihl 026 query - purchased 2nd hand
- Thread starter macmurdo
- Start date
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doesn't look good, but kinda blurry.
That's not really wear. The tooling marks on the left are pristine.
Either too lean or straight gas in that saw's history.
Either too lean or straight gas in that saw's history.
you need to find out what damaged the piston and fix that. if it was straight gas, that's easy. but it could be an air leak. also, the cylinder may well be damaged also. first thing to do is a vacuum and pressure test. there are various threads on here detailing how to do that. you will need a mitey vac or something comparable. you need to do both tests. after that's done, remove the cylinder and get a look at the damage. you can also check the crank and rod bearings for wear or damage at that time.
in the photo, it looks like someone may have cleaned some of the carbon deposits out of the exhaust port but just got the stuff close to the piston and left the rest of it. if you take the cylinder off, and it turns out to be re-usable, clean the rest of that out.
SteveSr
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That wear pattern sure looks odd. The FW side of the piston is well worn but the PTO side is near pristine. I would guess that there was/is a FW side seal leak that raised cylinder temps on the FW side causing the wear. This family of saws is known for FW side crank seal leaks.
If you do have to tear it down you need to determine if the cylinder and piston are OEM or AM. Pressure and vac test is in order first.
If it was me I would take the top off, crank the saw, and while it is idling squirt some starter fluid down behind the fly wheel. See what happens. If nothing it is not likely a seal leak on that side. If it revs up or kills it that would throw a flag. Make sure the screws holding the jug on are all tight as well..
If you want to do the clutch side you will have to take the clutch off to spray that seal. Still easier than all that vac/ pressure BS. Even if it has a leak you are going to have to find it.
All that vacuum pressure tells you to go get some soapy water or something to see bubbles. And, you will have to actually pull the flywheel to do that.
If you want to do the clutch side you will have to take the clutch off to spray that seal. Still easier than all that vac/ pressure BS. Even if it has a leak you are going to have to find it.
All that vacuum pressure tells you to go get some soapy water or something to see bubbles. And, you will have to actually pull the flywheel to do that.
crank seal leaks don't always show with pressure, which is all you're going to get by running the engine and using soap. if they are leaking on the exhaust stroke, which is more common and which is what pulls in air from a leak, the soap test isn't going to show that from the outside. but whatever. he should absolutely do the vac and pressure test after reassembly anyway, so how much more trouble is it to do it before?
Good Lord.
