piston seizing up.

I have a 01 yz 250f, I just installed a new cyclinder and went with a je 13 1 high compression piston, started it up and it was fine then took it out to go riding and rode around for a about 5 minutes then It started shutting off, at first though it was my carb, it was all adjusted wrong, so we got home, and rejetted the carb, it started right up, then it just stopped, it seized up, we got it unseized with some oil down the spark plug hole, we just went to a 5 20 oil today and cleaned all the oil lines out, It is getting much better oil pressure now, that might of been the problem. just wondering what some suggestion are about breaking it in, and if you think it will. we ran it for 15 seconds at a time then shut it off today, then rode it for 40 seconds it seem sto be doiung better now, it is very tight still, it feels like u are kicking over a 500,lol.

First, I definitely would not continue riding it. Pull it apart and look at it all, maybe you forgot to add oil, or something went wrong, but the truth of it is, you could be SOL all those parts.

Did you loosen the oil line to the head and make sure there was oil coming out there when the motor ran?? That's the check for the oil pump, and I've seen pump failures on other brands/motors.

Did you get the piston ring "end gap" correct?

If you did not as the rings heat up and expand the ring end gap closes and this will cause the piston to seize.

If that thing seized you're going to have to rebuild it again.

chances are, you have seized the intake cam. not the piston.

yeah sounds like an over torqued intake cam cover

try checking your cam chain tentioner.,.....if its too tight then you will have a hard time kicking it over....maybe...couldnt hurt to check

try checking your cam chain tentioner.,.....if its too tight then you will have a hard time kicking it over....maybe...couldnt hurt to check

the chain tentioner is spring loaded more than likely not the issue like sunru said it is more than likely the intake cam. Check the tork and for crap in the bearing surface.

I checked the cams, all that is good, it is definatley the piston, it was tight as hell when we test fitted it, completely forgot to check the ring gap, I fired her up today, and it seems like she is doing good now, i rode it around my block a couple times and it is running good, just taking it very easy right now. I got much better oil pressure now after we cleaned all the oil lines and replaced the filter. hope fully a little more breaking her in and she will be good, thanks for all the help.

I checked the cams, all that is good, it is definatley the piston, it was tight as hell when we test fitted it, completely forgot to check the ring gap, I fired her up today, and it seems like she is doing good now, i rode it around my block a couple times and it is running good, just taking it very easy right now. I got much better oil pressure now after we cleaned all the oil lines and replaced the filter. hope fully a little more breaking her in and she will be good, thanks for all the help.

The above bold statement scares me. A piston should NEVER be tight in the cylinder.

Did you check the cams or the cam journals?

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