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Anybody have an opinion on what DESTROYED this piston?

special tool

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Jun 15, 2008
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This is a piston from my TS760 Stihl cutoff saw.
My guys :)rolleyes:) said that it had merely run its course and died.
The inner filter was slightly off the seat when I inspected it, the outer filters were secure.
But can this be from some dust in small amount of time, OR does this look like regular gas being put into a 2-stroke $1,400 saw?:confused:

Either way, the bottom is still smooth, so I am doing the top - I was just looking for opinions.
 

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482budget

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It looks like thermal nuclear meltdown, no oil inthe fuel would normaly sieze it up but I would say lean out, someone messing with the high speed jet:)
 

DigDug

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Tool - Is that the exhaust side?? Do make sure you find what caused it before doing the top end and have it happen again. The air filter leak could have been the problem letting in to much dust particles . Were you cutting dry or wet? I would definitely put in new crank seals just for good measure . Make double sure the gas is mixed correctly or richer than recommened. Check that the carb intake boot is not cracked or leaking. Good luck with it. Doug
 

Muffler Bearing

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all good stuff to look for, but I have to add that my brother is an arborist and he runs only big stihl saws, and every once in a while one just hits the point and ends up looking just like that. I think hard working 2 strokes are always working right at their limits.
 

Deerehauler

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Looks like lack of oil to me-thats what the piston in Dad's Lawnboy looked like after I added what I thought was 2 stroke gas and mowed the yard. It REALLY hammered at the end.
 

JTL

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Looks to me like it ran on strait pump gas, with no oil.
Just like the piston in my mothers weed-eater when she poured strait gas in it, then couldnt figure out why she couldnt pull the rope after it died!
Jason
 

JDOFMEMI

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Looks to me like a case of either no oil, or at least not anywhere near enough oil.

Got to love guys like that. "I don't know whats wrong, it just quit"
 

nzpatch

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if its dust it will normaly were the intake side of the skirt, leaning out the exhaust side ,from heat, and no oil the skirt all around but worst on the exhaust side. is the small end pin showing hot marks? the spark plug tells alot too about tune .
 

Squizzy246B

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That looks identical to many I have seen from Stihl before they improved their air cleaner system. I'd need to see the whole piston and head but its looks like dust to me.
 

RonG

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I am not sure what the cause was but if it was no oil then I would be looking at the bottom too since it also depends on the fuel mixture for lubrication.Ron G
 

special tool

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Thanks for the input, guys.

The pin and the bearing are fine, not even discolored.
The enjgine still turned over easily....TOO easily.:tong
 

stock

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We have moved on and now were lost....
For my two cents it looks like a lack of oil as the lack of ceramic on the piston would exclude the dust theory.
 

Squizzy246B

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Thanks for the input, guys.

The pin and the bearing are fine, not even discolored.
The enjgine still turned over easily....TOO easily.:tong

Then its almost certainly the dust. I chernoybled a Husky last year that was almost 6 years cutting dry and the piston is very much the same. You crack a ring out and it bashes the head. The rest turn over fine.
 

special tool

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Then its almost certainly the dust. I chernoybled a Husky last year that was almost 6 years cutting dry and the piston is very much the same. You crack a ring out and it bashes the head. The rest turn over fine.

Starting to reach that conclusion.
The innermost filter was off the seat (you must manually push it down on the older Stihls inside the larger one).
Plus, I mixed the fuel and set the high and low on this carb myself....and Lord knows I myself never make a mistake.:D
 

Squizzy246B

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The heat pattern is wrong for a lack of oil failure.

The Stihl's are a little fiddly in their air-cleaner arrangement and lack adequate surface area for dusty operation. My Huskies have twice the surface area of foam and will still be well clogged after a couple of days hard work. I carry two spare foams in a zip seal bag all oiled up ready to go. Washing the foams is way cheaper than buying paper elements. I spoke to Husky when I chernobled the 3120K (120cc) and said to get the foam almost dripping with filter oil.

I couple of my competitors (who cut dry like we do) don't do a lot of servicing and the blow a Stihl Qwik Cut in about 12 to 18 months. The pistons are always identical to yours.
 

powerjoke

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could be a couple of things.

if its on the exhaust side it was ran a little lean and got hot

if it was on the intake, i would say it's no oil.

those are just two and either one maynot be right

Pj
 

Squizzy246B

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If it failed due to lack of lubrication there would be a big round blue and black ring on the underside of the piston and also visible in the top, as well the skirts would show the expansion and heat marks typical in two strokes running lean.

This is a mechanical failure from FOD ingestion over time. I spent some years doing engine failure analysis for a living and this is typical...almost classic. The fact that the bottom end is fine also tells the story.
 

willie59

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If it failed due to lack of lubrication...

The fact that the bottom end is fine also tells the story.

There's your money quote. I agree with Squizzy. Remember folks, the reason two strokes, like chain saw engines, mix oil with gas is mainly to lube bottom end since they don't use crankcase oil, not necessarily for lubing top of piston where failure occured. Yes, the gas/oil lube is necessary for lubricating rings and piston interface with cylinder, but if this piston/ring failure had occured from prolonged lack of lube, the bottom end would be hammered as ugly as the piston. My 2 c
 

powerjoke

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i was primarilly talking about cylinder score.

how about a pic of the cyl?.....if you can get youre camera in there lol

as far as the Valve thing.... not all 2 strokes have them.

Pj
 
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