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A piston or B piston

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I'm sure there are a thousand threads about this but I can't find one...:cheers:

What size is the 'B' piston and when is it necessary? I've used a Wiseco on my last 2 rebuilds but they don't differentiate a or b, just 66.4mm. I get a slight knock /slap when the engine is cold but then disappears when she's warm. I'm thinking I'll go all oem this time around so I need to pick one. Thanks, Larry.

2000 CR250

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Honda no longer make the A piston,if your able to find one it's old stock.

Difference is to small to notice

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Hmmmmm. If the 'a' is larger but the difference is negligible does that mean it should fit a standard bore? It looks like some measuring is in order. The vendor I'm looking at offers both.

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your cylinder should be marked A or B on the left side and then your suppose to use the matching OEM piston. But as others said, I've always heard it doesn't matter.

However, I have a 99' CR250 and I cannot find the "A" or "B" marking on my cylinder...

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Mystery solved. She's got an 'A' cylinder. That stamp looked like an arrow...:ride: montigeau, the stamp is on the left rear thread bore. I found a pic of it in my FSM when I got home tonite. Thanks for the responses guys, time to shop.:cheers:

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