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    Piston & Rings 2001 CR250, Top End Rebuild

    A piston & rings change in a 2-stroke should be done about every 40 to 60 hours of run time. Mine was well overdue. The cylinder was still in good shape, but the piston had definitley lived its life. Check out the shiny new piston in its new home.

    -After we put the new piston in, it did not want to fire up right away. We finally determined that it either had water in the cylinder or too much 2-stroke oil used in assembly. We took the head back off and found it too be very wet inside the cylinder. Once we cleaned the cylinder out and made sure the gasket was sealing it fired up and ran strong.

    -It seemed to idle alot better probably due to the higher compression and/or better sealing of the new gaskets. I have heard that mods such as the porting job that has been done to this bike can make it not want to idle cleanly. Once you are riding, the idle only comes into play while holding the clutch in on steep downhills and you just have to blip the throttle occassionally to keep it running. I have only ridden with the new piston down the street etc. but it does feel a little stronger, and I am happy with the result. hopefully with a few adjustments on the air screw the idle will continue to make improvements.

    Click Here for a youtube video that documents a top end rebuild on a Yamaha 2-stroke.

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