Stihl 011AV Low Compression

[cume71]

I bought a Stihl 011AV at a garage sale for $5. It is in great shape, but the carburetor was disassembled. I put it back together, repaired a loose contact to the spark plug and now have good spark. But it will not start, not even a pop, even with fresh gas (or starting fluid) into the carb. I checked the compression with a Sun automotive compression tester(with valve in the tip) and I get max 50 lbs after 10 seconds of pulling. I took the muffler off and the cylinder walls look good. Any other reason I get such low compression?

 

[NuConcepts]

it could be your rings are shot.The piston and cylinder might be scored you cannot always see everything. I would pull it apart. I doubt your compression tester is off that much.

 

[blsnelling]

You're going to have fun with this one. Don't loose the big end roller bearing needles. They'll fall all over the place. Use grease to hold them on the crank when going back together.

 

[cume71]

Thanks for the response, how do you tell the rings are bad?
What does a set of rings cost and where could I buy them?

 

[czar800]

Welcome to AS, five bucks well spent, wheres the pictures

 

[NuConcepts]

if i were you i would just pull the cylinder before you buy any parts and see what happened, that way you can actually see what you need. Im not sure if the parts are Nla thats an older saw. Someone on here knows where you can get them or has them though.You can tell if the rings are shot by a simple compression reading. One thing i use to do is pour a little 2 stroke oil down the cylinder, hook up the compression tester and see if the compression went up significantly compared to a test with no oil. that would tell me if there worn.

 

[cume71]

Not good news

I took the cyc. head off. The piston is really scored. The cyc head is not as bad, but there is some scoring at the bottom of the stroke near the exhaust port. I wouldn't mind replacing the piston and head if I could get the parts reasonably. Anybody have a source? I attached some pictures.

I will also have to rebuild the carb, since the gaskets looked pretty bad when I put it back together.

 

[blsnelling]

You didn't let the rod come off those needle bearings did you? Yeah, you need a new piston. I'd try some acid to clean up the cylinder. Then a ball hone would be ideal. If not, use some wet/dry sandpaper. My Dad has an 011AVT that was in similiar condition. We sanded/polished the piston, cleaned up the jug and threw it back together. It runs great.

 

[cume71]

Thank goodness I saw the warning about the needle bearings on another post before I took it apart.
I will hone out the cylinder and polish the piston. I would still need a new piston ring, it is also scored. Any good source for that?