What do yall think could have caused this?

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Jkstihl

Chainsaws make me fap.
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All i can guess is that somebody used a screwdriver as a piston stop.

Wrist pin bearing is good.
Big end bearing is good.
No end play on either end of crank. So im assuming those bearing are good also.. Rotating assembley is smooth as butter.

Havent split the cases yet. There was no fragments or anything inside the crank case not even pieces missing from piston.

Anybody experienced this before? Bought it like it is and pulled carb to rebuild it and saw the damage on piston. Saw would idle but wouldnt take fuel.
 

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You could be right about the piston stop. Someone sticking a screwdriver or some other object into a port. I had a Jonsered 670 someone used one of those piston stops that goes through the spark plug and it cracked the widows on the piston. That is why I never use piston stops of any kind. This stuff is just aluminum after all.
 
I've never seen it that severe but when the butterfly screw passes through the intake you get a similar effect.

Throttle plate and choke plate screws are still there. Im baffled.
 
Agree with Harley, Would like to see some more pic's especially of the intake side of the cylinder. Looks to me like you are showing the wrong side of the cylinder. Would be curious if someone has modified the ring tucker/air director or it shows heavy wear or possibly has broken off causing skirt damages to the piston. This was a subject that was brought up here recently by another AP.
 
If the saw had ingested something there would be scoring on the cylinder wall where it wedged in between the piston and cylinder. Your picture from the side you show does not have any scoring.
 
It’s he latest in piston porting. Trying to save on weight. It’s a known fact that if there isn’t any material there then there isn’t any friction so it should move better... I mean that’s how it works right?
 
Just a theory but im pretty sure this isnt a factory nut that was holding the intake flange on...the other nut that was factory is matching up to the damage pretty good.

Pic of intake side of cylinder
 

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Oops this is intake side
 

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It’s he latest in piston porting. Trying to save on weight. It’s a known fact that if there isn’t any material there then there isn’t any friction so it should move better... I mean that’s how it works right?
It's done for up high. You don't cut at idle after all WOT is all that's needed.

#weightreduction

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Now that's a better pic. The ring Tucker tear drop is totally gone from the roof of the intake. It looks as if someone has widened the crap out of that intake port Wondering if the tear drop broke off or it was ground out? Either way throw that pos away no matter how good the bore looks.
 
Now that's a better pic. The ring Tucker tear drop is totally gone from the roof of the intake. It looks as if someone has widened the crap out of that intake port Wondering if the tear drop broke off or it was ground out? Either way throw that pos away no matter how good the bore looks.

I’m following this for further learning. Could you mark on the photo what you’re talking about?
 
I have some cyls that I can take a pic and show you. The piece that's missing is normally just offset from the center of the port coming down from the roof. Similar to the failed piston pic.

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