piston replacement on a 400 1999

1 reply to this topic
  • 5valve

Posted February 15, 2008 - 06:00 AM


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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  • 5valve

Posted February 22, 2008 - 11:50 AM


Through dealer, managed to get answer from pro-x.
They have 91.95 in production, although not listed.


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