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Hi All,

Im in the process of replacing the piston in my 04 ish crf450. I cannot for the life of me work out whether I need an A B or C piston. Ive tried to measure the bore with verniers and get 98mm at the bottom and about 95 at the top. The Piston reads a similar size. I spoke to a shop today and was advised to get an A as having a larger B or C will potentially damage it. Ive also been told to get a B as A's are generally only for newly honed/new barrells.

I do not have a clue and just want to ride the dang-nabbid thing. Advice extremely appreciated/needed.

Thanks.

Dan

I edited your post to remove the F bomb. Ken prefers this site to be family friendly, please oblige...

I replaced the piston in my 05 every year and always bought the standard size offered. Never had a problem.

You get one choice from Honda ===> 13101-MEN-730
Wiseco says ===>4820M09600
Pro-X is the only supplier I see doing the A,B,C thing.

With that said, It's clear your measuring the cylinder wrong. You need a bore gauge. You cannot do it with calipers.

The standard cylinder bore is 96mm. The service limit is 96.05.

Side note: I thought we determined your bike to be an 05 based on the VIN?

The piston OD service limit is 95.87.
The cylinder wall to piston clearance is 0.020-0.045mm.
The Pro-X A,B,C sizes range from 95.96 to 95.98.

So....as long as there isn't anything silly going on with your cylinder any one of these pistons should be fine. I would recommend double checking cylinder bore with the proper tools and ordering the standard Honda OEM piston part number above.

Skip all the hub-bub...

Oops sorry!

Ive managed to come to a decision. Buying a Prox B, sticking it in and going for it!

Cheers!