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cracked kx250 92 piston


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A couple of months ago i posted that i had just fit a new piston to my 92 kx250, and that after revving it up the piston totally cracked in half and left a mess in the bottom end.

Ive now had the engine rebuilt and found out the barrel isnt from a 92 bike but from a 91, so ive fit a 91 piston.

Does anyone know if that could explain why a new piston cracked in half after being revved up? (ive been told a 92 piston is 1mm bigger than a 91)

Thanks

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Ah i thought the new piston was bigger not smaller.

It did run with a 92 piston but only just. I managed to start it a couple of times after many many kicks, and the last time it started i wound it way too far and then the piston cracked.

The cylinder isnt worn out its in pretty good condition,ive just had the engine rebuilt and it didnt need replating.

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We managed to get this 93 yz125 started that my buddy brought home. We were told it had a new piston, but that something was not right with the carb. You know, the usual. So we kicked and kicked and finally drug it behind the four wheeler until it started. It actually ran ok when you wrang it out hard, but on the bottom end it was nothing but bog. Pulled the cylinder and the piston was 2 sizes too small! Cylinder was 1mm over, and it did indeed have a freshy new piston in it, however it was STD size! We had it re-plated it and installed the correct piston. Neat little bike after that! Unfortunately he just sold it this past weekend. I never really got it out on the trails, just zipping around the house. I was shocked that the bike started and ran that way though!

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