Maintenance & Technical > KX500 Original

kx500 piston seizure

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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.

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