Piston Failure Cause

[drf255]

This is a MS260PRO project I bought from a forum member.

Interestingly enough, the cylinder and crank appear to have survived this calamity.

The intake side is perfect with no scoring at all.




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[angelo c]

I'm not sure that one will buff out.

 

[o8f150]

little bit of jb weld and it will be fine,,,,,,, looks like it was run lean

 

[big t double]

I'm not sure that one will buff out.

Pessimist.

 

[drf255]

Was able to get a new Stihl OEM 44.7 piston and rings for $25 shipped on FleaBay. We shall see.

 

[1Alpha1]

It's gonna take more than just Scotch-Brite and some elbow grease to clean that all up.

 

[nmurph]

It was probably caused by a skirt that was worn thin, started slapping and broke.

It's a good idea to blow the saw off well bf you remove the cylinder.

 

[Adirondackstihl]

It's a good idea to blow the saw off well bf you remove the cylinder.

+1

 

[drf255]

It was probably caused by a skirt that was worn thin, started slapping and broke.

It's a good idea to blow the saw off well bf you remove the cylinder.

Agree.

Except it's got more than sawdust in the crankcase..

 

[pantelis]

 

[drf255]

I plan on putting the jug back on before cleaning it.

I wanted to look inside the case before I made any efforts.

 

[drf255]

I think I know what led to this saw's destruction, I may be wrong though.

Under the clutch, the oil pump drive tit snapped off halfway down. It also ground down the oil pump. The surface almost looks like it was machined with a mill.

I think the prior owner put a non-pro clutch drum with no notch for the drive on and then tightened everything down. The clutch cover then bent the pump drive and then the saw was run with this amount of drag on it. So much that it ground metal down.

I think this was the cause.

 

[drf255]

No notch in drum, so pushed down and ran.





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[Cedar Row]

This is a MS260PRO project I bought from a forum member.

Interestingly enough, the cylinder and crank appear to have survived this calamity.

The intake side is perfect with no scoring at all.

View attachment 397719View attachment 397720View attachment 397721


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I am working on a MS 260 that had piston damage similar to this, but not as severe. The piston was badly scored on the exhaust side, enough to essentially weld the piston rings to the piston. The opposite side was fine. The owner of the saw told me the muffler outer shell had cracked, and he put on a new one. I am assuming that carbon or pieces of the broken muffler got in the cylinder. Not sure why or how the muffler cracked/broke, it was only the outer part of the muffler, he did not remove the inner part and gasket to repair it. Just thought I'd point out this cause of similar damage.

 

[drf255]

Thank you

 

[Cedar Row]

Just got to wondering if the crankshaft was damaged in my project saw. Did yours have crankshaft damage?

 

[drf255]

None I can see

 

[Cedar Row]

Thanks! Hope mine is ok too. It is always "fun" to separate a crankcase.

 

[ft. churchill]

I dunno what caused it. but I am certain that is one of the ugliest piston failures I ever seen. Wow!

That leads me to wonder how that saw will run/hold up after a new piston is stuffed in it. Post up when ya git 'er done.

 

[sawsawsaw]

I have seen the exact same piston damage on two 026's and an 024.

I always assumed (as nmurph mentioned) it was piston slap and tickle.

Good luck with the project !

Maybe some crazy canuck will send you an 038 mag cylinder to put on this saw. ( winkwink - just kidding )