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5valve

piston replacement on a 400 1999

2 posts in this topic

Soon expect renewed cylinder. It will be made in zero tolerance, thats 92.00.

Am in doubt as to use original or pro-x piston.

By manual, piston diameter should be between 91.945 - 91.60. Probably new yamaha piston varies in this tolerance.

In prox catalogue, there are 3 sizes, A, B, C, (91.92, 91.93, 91.94).

So the biggest pro-x oversize is still smaller than minimum service limit diameter given in manual.

If I check back, 1998 has smaller piston size service limit, that's 91.92-91.935.

I presume they are offering '98 model tolerance for all 400's.

Piston I took out, was running more than 3 years, closer to 5, was measured 91.95.

Those are the only brands, i can lay my hands on with decent rebate, so no other piston brand is an option.

Any thougts?

Contacting prox is as talking to wall.

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