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  1. #1

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    Why do you have to match pistons like this??

    I don't understand why the the specific oem pistons (A,B,C, or D) should be matched to the correllating number stamped on the cylinder...Does anyone know? So, does it still matter if you use an aftermarket piston?

    0-5 =A piston
    6-10 =b piston
    11-15 =c piston
    16-20 =d piston


  2. #2
    Moderator OsideBill's Avatar
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    It is to accomadate varying manufacturing tolerances from the factory.

  3. #3

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    So, would it make that much of a difference if an A piston was used in a D cylinder (for example) if it was a standard 80mm cylinder that had just been replated?

  4. #4
    Moderator OsideBill's Avatar
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    If a cylinder has been re-plated, then it has been honed, what size is it now? The manual recommends
    0.100 ~ 0.105mm (0.0039 ~ 0.0041in) clearance for OEM pistons, Pro-X is the same. Wiseco's run a little more clearance usually .005-.006". Generaly when you have a cylinder replated, you send the piston in with it and spec what clearance you need and they hone it to match.

  5. #5
    CHICKA WAH WAH bren's Avatar
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    Quote Originally Posted by darrengee View Post
    So, would it make that much of a difference if an A piston was used in a D cylinder (for example) if it was a standard 80mm cylinder that had just been replated?
    no, you match the piston sizes to get the 4 thou tolerance.

    this is not a yamaha thing, but an engineering and manufacturing sizing formula

    after market pistons have the same sizing formula

  6. #6

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    I was looking at buying a standard 80mm bore cylinder from US Chrome that has already been re-plated. I was also going to buy a new standard size oem piston from Yamaha. You think that will be safe? Or, am I better off sending them my new piston, rings, and used cylinder to have replated?

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