Piston diagnosis

[Franksmallengine]

Recently got a husq 51 1998 model plan on restoring. The piston has disassembled its self and I am curious as to what happened so it doesn’t again. I have no knowledge as to its history when I got it it was locked up from piston skirt jammed in the crank and the smell of bad gas in the crank case was enough to over power the pb i used to free it up

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[Franksmallengine]

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[Franksmallengine]

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[Franksmallengine]

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[Franksmallengine]

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[Franksmallengine]

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[Franksmallengine]

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[Franksmallengine]

Entire saw covered in oil / dust mix as seen above had 1/2 inch in some spots


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[jacob j.]

It looks like debris got in there and broke the chunks out of your piston. Maybe something came in through the intake port? Were the main bearings
and big end rod bearing still intact?

 

[drf256]

I’d bet the intake skirt is much thinner than the ex side of those skirts.

The intake skirt is the thrust side of the piston. When it wears, it thins out and the piston starts to rock and slap in the bore. Then the skirt cracks, pieces come loose, and shrapnel goes round and round till everything else breaks too.

That’s my guess.

 

[Lee H]

I'm with Al on that one. Looks like that piston has a lot of time on it and
had some serious piston slap.

 

[rogue60]

Long term oil test- yeah I wouldn’t run whatever that crap oil is in any my gear lol

 

[BuckthornBonnie]

I’ve seen a 51/55? that ingested the choke plate.
It was still in the crankcase, though, and pretty obvious during tear down.

piston slap or ingestion of something… agreed.

 

[kneedeepinsaws]

I’d bet the intake skirt is much thinner than the ex side of those skirts.

The intake skirt is the thrust side of the piston. When it wears, it thins out and the piston starts to rock and slap in the bore. Then the skirt cracks, pieces come loose, and shrapnel goes round and round till everything else breaks too.

That’s my guess.

This is the main reason that pistons should be replaced in 2 strokes. The saying “ if it ain’t broke don’t fix it” does not apply here. Piston may look fine and have good compression but the skirt may be thin. Service manuals will specify the tolerances.
Another good reason to just pull the top end yearly and just check things out.

 

[Franksmallengine]

Only thing I found was the crank seal spring missing (and bad gas) from the tear down i can say it had plenty hours but the ring and piston was perfect where it didn’t eat itself(even found crosshatch). My guess is it ate the spring and died the piston skirt was the same thickness from intake side to exhaust


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[Basher]

Are there any marks on the connecting rod, front or back side that would indicate the rod and piston skirt may have dinged each other?