kx500 piston seizure

[bruuuuup]

I only had 2 hours on this brand new motor and the piston and rings cam apart on the exhaust side and destroyed everything in the jug. I run it at 40:1 and it smokes a lot is this to rich? Also I had a leak in one of the rads and I rode it for a little bit and it started to idle really high so I killed it then the next time out she blew up, Could that be the issue?

[kaw rider]

post pictures of what the piston looks like.

[jonny500]

what piston were you using? piston rings almost always seize or bind on the exhaust port as this is the hottest part of the engine.
40 - 1 is fine with a good quality 2 stroke oil.
lack of coolant/ leaky rad will cause over heating.
you say the motor was fast at idle, this is a sign of a lean carburation. this would make the engine to run hot, causes are air leaks from the inlet, crank seals or anywhere else that would let in air to upset the fuel air mix. the other cause of lean carburation is not enough fuel, blocked jets or wrong jets.
how long did you run the engine in for. were you working it hard. i would say 2 hours is just enough for running in but i would probably take it easy  for another hour or so (depending how much the motor had cost me)
some times its just bad luck but i would try to find the cause before rebuiding
hope this helps

[jonny500]

post a pic of the plug too

[greenstreak]

A high idle is usually a sign of an air leak.  An air leak will give you a very lean mixture that can cause a seizure.  I would be looking for a hole in the intake boot or the boot to the airbox. The dry side of the crank seal may be leaking as well.  The wet side sounds like it is leaking because of the smoking you spoke of.  If you suck in transmission oil because of a bad  wet side crank seal it will smoke like crazy.

[bruuuuup]

I already sent the motor BACK to get fixed, but here is the plug pics, the piston and rings came all apart on the exhaust side and smashed all the pieces into the plug and the head, I mean I could hear it destroying everything, chunks of the ring stuck all in the head, The piston had some burnt oil Below the bottom ring (brownish color) , greenstreak it is interesting that u say the seal cause the gear oil was a silver or gray color the two times I drained it, would the gear oil turn that color from the premix fuel (pump gas klotz r-50)   Thanks for the help I just want to find out what the hell happened....BTW this insane motor pulled the whole time till it smashed the plug to nothing, CRAZY

[Polar-Bus]

I already sent the motor BACK to get fixed, but here is the plug pics, the piston and rings came all apart on the exhaust side and smashed all the pieces into the plug and the head, I mean I could hear it destroying everything, chunks of the ring stuck all in the head, The piston had some burnt oil Below the bottom ring (brownish color) , greenstreak it is interesting that u say the seal cause the gear oil was a silver or gray color the two times I drained it, would the gear oil turn that color from the premix fuel (pump gas klotz r-50)   Thanks for the help I just want to find out what the hell happened....BTW this insane motor pulled the whole time till it smashed the plug to nothing, CRAZY

Obviously you had a total piston granade failure. My guess is your cylinder was junk to begin with, and someone just threw in a new piston.  We can't help you without pics of the piston and cylinder. Also be more specific with details  in regards to the prior "brand new motor"  ?? 

[Danger4u2]

The gray color in the oil is from the aluminum plates in the clutch.  Mine is always like that, I change it often, it's only a few buck to change oil.

[dave916]

The gray color in the oil is from the aluminum plates in the clutch.  Mine is always like that, I change it often, it's only a few buck to change oil.

the grey colour in gear oil could be caused by a water pump seal, especially if you gear oil level is rising and water level going down,  i use steel plates in clutch, [suppose to act a bit like a flywheel weight]