Newbie rebuild

So I'm new to the forum as well as mx bikes. Recently I got a 99 kx250 that the previous owner said was locked up. Before anybody says im over my head getting a 250. I've rode plenty of sleds and quads. My only experience on a bike is a ttr125 though. Found out that I could kick it over but was stiff. I've got the cylinder off now. It appears to be okay. The piston is another story. The exhaust side skirt is sort of flared out at the bottom. Which is why it was stiff to turn over. Also 2 reeds were chipped. What gets me is why the exhaust valve and under the covers were covered in a gray gritty film. I plan on doing a full rebuild replacing the crank. I'm just looking for an explanation on why it grenaded.






The gray looks like aluminum.  You should do a replate and crank for sure. The engine will last a looong time after a full rebuild.  


250's aren't bad if you respect the throttle.  You can lug them around off the pipe until you get used to it.  They aren't like 125 where it's off and on, for the most part.

2 strokes don't need a reason to grenade.


but a few reasons are.


piston slap


play in the bearings (all of them)


too lean.


wrong fuel oil mix (not enough oil)


detonation. (usually because of too low octane)


there is a bunch more, but these are the usual ones.

Edited by Excitable

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