Brand new to the forum and never seen this before

[maowwg]

So, I was working on a Poulan Wildthing and the front of the piston at the exhaust is pristine. As is the cylinder almost all the way around. Compression felt marginal, gauge says <90psi. And as you'd expect with marginal compression, it starts, runs without great power and then as it heats up, and dies.

I noticed that the cylinder is scored above the corner of the intake on the flywheel side. Never seen that before. All the scored pistons I've run into so far are scored at the exhaust side. (This is hobby for my son and me and only saw #24 for us, so we haven't seen everything).

I'm just wondering what caused that? I won't fix it with a market value of only $80 to $95 repaired, but otherwise the saw is like new.

What's caused that?

 

[trains]

piston ring retaining pin came out of the piston ?

take it apart and have a closer look.

 

[Mad Professor]

Trains has a good possibility.

It ate something hard on intake side. Could have came through intake, or be a piece of bearing also.

Could be a good parts saw for someone, or if you could find a parts saw. Agreed I'd rather spend my time fixing a "pro" grade saw.

 

[maowwg]

That's a great thought. I didn't consider that.

Not saying anyone's wrong, but on a Poulan with a single ring, isn't he piston retaining pin at the middle back, essentially where the carburetor is located? If it comes out it should hit the wall of the cylinder before it escapes into the engine and score the snot out of the wall 180 degrees from the exhaust port? That part of the cylinder is brand new condition and this is almost 90 degrees to the exhaust port by the flywheel..

 

[TRTermite]

Could the wrist pin clip get into the transfer and return in intake air/mix?

 

[anlrolfe]

Top of the piston has pock marks
I'm thinking rod bearing, crank bearing or bearing cage.

 

[maowwg]

So is it fair to say to the saws owner that a piece of the motor, not sure exactly what it is, broke free and got injected into the combustion chamber then stuck between the piston and cylinder and caused that? I.E. not his fault and not a result of poor maintenance or abuse?