I need a piston diagnosis...

[NoSecondChances]

Pictures from a buddy's melted 800. I have an idea of what happened to it but want to see what some others think to confirm/deny my theory.

History - Sled blew a rod bearing on the crank and was then re-built. It had a rebuilt motor, ran strong for 4 days, then melted the piston on the trail up to the alpine about 6 kms from the truck on a March morning (-5C). Sled is bone stock other than a single pipe and can (forget the manufacturer - CPI maybe?). It was not running hard at the time, it was not overheating and the jetting was correct. Top of piston looks good. There was no indication that anything was wrong before it stopped running.

Sled melted MAG side piston on the intake and exhaust sides, no real damage to the top. Crankcase on the MAG side was full of oil when it disassembled (6 months later - don't ask why it took so long).

See attached pics.

Thanks in advance.

NSC

 

[RKT]

Pictures from a buddy's melted 800. I have an idea of what happened to it but want to see what some others think to confirm/deny my theory.

History - Sled blew a rod bearing on the crank and was then re-built. It had a rebuilt motor, ran strong for 4 days, then melted the piston on the trail up to the alpine about 6 kms from the truck on a March morning (-5C). Sled is bone stock other than a single pipe and can (forget the manufacturer - CPI maybe?). It was not running hard at the time, it was not overheating and the jetting was correct. Top of piston looks good. There was no indication that anything was wrong before it stopped running.

Sled melted MAG side piston on the intake and exhaust sides, no real damage to the top. Crankcase on the MAG side was full of oil when it disassembled (6 months later - don't ask why it took so long).

See attached pics.

Thanks in advance.

NSC

Few things come to mind...

1) It looks like the ring broke...

2)Usually failures that look like yours are the result of an oil failure (lack of oil) or water injestion..

Kelsey

 

[coreyt700]

Can't tell 100% by the pic but it looks like you lost the little pin that holds the ring from spinning and it spun and caught a port and broke. I would say deffinately broke a ring. Why the ring broke could be oil failure or water injestion as previously mentioned (most common) but I can't see the ring stop pin (or whatever the tech word is) in the piston and there is definately a chunk of ring missing.

 

[gus bohne]

Correct me if I'm wrong but I see no broken ring, just a stuck ring, locating pin might be there, end of ring that is NOT welded in is free and just sprung the gap open..

you got water, snow injestion maybe.. not a good view of the piston.

sorry
Gus

 

[NoSecondChances]

Sorry - Ring is not broken, the gap is there and the ring has been expanded off the back of the piston (can't see in the pic) but the ring is intact and is as Gus said, just sprung the gap open (sorry not a great pic - they were sent to me I didn't take them). The locating pin is still there as well.

Kelsey pretty much confirmed my suspicion, I think it was a lack of oil as well. I would have suspected snow ingestion too if we were weren't on a hard spring trail heading into the alpine (no powder on the trail) but I think it was lack of oil as well. I guess I'll have to inspect it closer next time he's down.

Thanks guys.

NSC

 

[madracer]

Head shows signs of a very white (hot) plug and no signs of seeing any oil at all.

 

[montanasledhead]

did you run a little premix in the gas while breaking it in
looks like a lean condition
if it sat after rebuild and injector pump was dry it may not have been oiling
I always check to make sure pump is primed after a teardown add a little oil in the gas and then brreak in the motor
have also seen this with a bad seal causing it to lean out
still I dont think you were getting oil
you also stated no powder on trail are you sure the idiot light works for overheating
????