Blown piston need help

[renos2]

Need help finding out what caused this burn down I have put 3400kms on this sled with no problems till yesturday was going across feild at maybe 40 mph and started to miss so I stopped checked the plugs and the #1 cylinder plug electrode was hammered shut so I pulled it home and tore it down.This is what I found wondering if some one can tell me what happened by the piston wash. I have not changed any jets or anything it has 148.5 in #1 Cylinder and 150 in #2 and #3 it also has attac on it could this lean one cylinder out

2001 Mountain Max 700

 

[TOM WRIGHT JR]

Check to see if the dowel that align's the rings is still there, it looks like the ring spun and hooked the exhaust port.

 

[renos2]

the pin is still there

 

[snowdad4]

check that carb for water or blockage in the jets. looks like a detonation lean burn. also look at the carb intake boot and the crank seal on the pto side. fresh quality fuel at the time?

 

[renos2]

how do you check the crank seal

 

[ryan7]

check your intake boots for a crack, they are getting old now and may have a crack in the one now

 

[snowdad4]

how do you check the crank seal

alot of times the spring in the seal will fall out and be behind the clutch. pull the clutch and visually check the seal for deteriation. no other way i know of without the sled running. was the sled running fine prior to burn down? if it didnt suck air, my moneys on bad fuel.

 

[spring snow hero]

pop the primary off and check the crank seal. blow any belts recently? the pto side makes me think so. looks like it leaned out and chewed the edge of the piston off and tripped a ring. sides don't look oil starved.

 

[renos2]

yes sled was running fine.will the pto side seal cause it to lean out

 

[M.M. 700]

What elevation? What kind of triple pipes? What was the outside temp at?

What pilot jets/needle position? If you were doing 40 you were probably running of the needle position not the main jet (wide open)

Doesn' the other 2 pistons look a little funny.....

 

[renos2]

3500ft ,Power INC pipes,-8C,55pilot,Needles 3 and yes the other pistons look funny to me to

 

[Givemeaboost]

I bought one like that that had two pistons melted. I couldn't figure out what caused it so I opened up the water pump to find that the nut came off the impeller, causing it to overheat .

 

[theultrarider]

Did you mybe get ahold of some ethanol fuel and you were jetted close to the edge for normal premium? That may have been enough to lean out enough to put you over the edge? Just a thought here. The other pistons look lean to me as well.

 

[Xrider]

Need help finding out what caused this burn down

You must be in the wrong section, isn't this suppose to be in the skidoo section??

 

[renos2]

checked water pump today and all good leaning toward compensator screw up

 

[dexter]

Jetting is not lean. when I had one i was quite a bit leaner on pilots and mains with the same pipes at the same altitude. Check that carbs are clean, a good soak in carb cleaner helps. Then check carb boots and crank seal. flush motor with pre-mixed gas to get rid of filings. with crank full of gas see if it leaks out of crank seal it shouldn't. This is not as good as a pressure test but it works. if no problem is found reassemble and fire it up at idle and spray starter fluid around crank seal and carb boots, if idle increases theres a leak. if not try it and read plugs to see if its lean also check choke circut to see if its sticking good luck

 

[renos2]

thanks I will give that a try and also unhook compensator

 

[#1Leaddog]

meltdown

I agree, all cylinders are to lean. Findout why and fix. Seal out is most likely cause. Or you were lucky for quite a while. I have found that if the needle is not quite right and you rode it a little bit different then normally it will cause this. Once you get to the meltdown point it does not take long.

 

[renos2]

do you mean crank seal

 

[#1Leaddog]

piston

Yes I mean crank seals. generally it is the big seal behind the clutch that goes bad. But not always it could be the other one. but with the piston on the clutch side burnt that would be my guess.