'02 KX125 engine dies at high rpms

[TotalNZ]

Here's another theory on the engine's fate provided by a bike shop's mechanic.

After he took a look at the piston, said that running lean was not a cause of the seizure. Based on where the damage marks are on the piston, it supposedly looks like the bike had been cold when it was given gas. So the piston had warmed up, enlarged, started to chafe on the other side and then get stuck finally on the other side where most of the damage is.

Isn't the piston made of some aluminum alloy?

Could the seize have happened just because the piston warmed up more quickly than the steel sleeve?

Yes definately, this is classic case of the probs a steel sleeve can cause.
As was mentioned earlier, the steel sleeve builds and dissipates heat differently than what the manufacturers intended. As a result the rates the piston and liner expand are out of sync and can cause scuffing and in some instances a seizure.

[citabjockey]

Yes, that is quite correct about cold seizure. You do have to have it fully warm before asking for lota power - esp when on a new bore and piston. Did you also have him look at the plug? If he is ok with it then you may be fine. My break in procedure still applies.

[Shadow]

No, I didn't show him the plug. Forgot to mention to you guys, that it's an old plug, and the pebbly surface was on it already when I put it in the bike. The current cylinder/piston usage did not cause that.

Got a new piston ordered, once it's here, will drop the cylinder and piston to a workshop to be fixed and I will make sure it will get within the piston/cylinder clearance specs.


Also picking up an '02 kx250 tomorrow. Will use that for a kx500/250 conversion project once I get a bit more money and find a suitable donor bike for the engine.

[Shadow]

 
Got a workshop recommended to me, getting the piston tomorrow, and then the cylinder is off to be fixed.

[Shadow]

Man, I do not get a break.

Got the bike back together, went to the track to break it in. Engine works fine, no issues with it now, but afterwards I noticed the swingarm pivot nut had disappeared. Good thing that the rear brake lever stops the pivot shaft from getting out on these kawis. Could've been an interesting turn of events otherwise.