365 piston scored

[tomalophicon]

Hi experts,
Today I bought a very cheap 365 Special that failed the pull cord compression test. Saw started without too much trouble but wouldn't idle and bogged and stalled with any throttle.

Pulled the cylinder and found minor scoring on the intake and exhaust sides (opposite each other). Any idea what might be the cause? Owner reckoned he lent out the saw and it came back like that.

Air filter looks clean and it's fairly oily in there. Ring looks ok.

Thanks in advance for any help.

 

[Gord404]

Probably an air leak some place or was straight gassed, I usually vac-pressure test them before I pull them down around 8 lb.'s to get a better Idea as to why.

 

[cuinrearview]

That piston does not look that old. I bet it has an air leak that someone never corrected when they replaced the last roached top end. Straight gas usually more evenly distributes the scoring around the piston.

 

[mountainlake]

In the snowmobile world that would be called 4 corner seizing caused by not letting it warm up and going to full power right away. The piston heats up faster than the cylinder and has no room left . Steve

 

[tomalophicon]

Probably an air leak some place or was straight gassed, I usually vac-pressure test them before I pull them down around 8 lb.'s to get a better Idea as to why.

Thanks. I was too eager but will test it all before I try to run it again.

 

[tomalophicon]

That piston does not look that old. I bet it has an air leak that someone never corrected when they replaced the last roached top end. Straight gas usually more evenly distributes the scoring around the piston.

No it doesn't look old. I was surprised by the lack of carbon on top.

 

[tomalophicon]

In the snowmobile world that would be called 4 corner seizing caused by not letting it warm up and going to full power right away. The piston heats up faster than the cylinder and has no room left . Steve

Makes sense. Thanks.