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  1. #1
    billy's gpr's Avatar
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    66v piston sizes

    i know there is a code on 66v cylinders,for correct piston size ,where is it,thanks bill


  2. #2
    Moderator beerdart's Avatar
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    Cylinders are marked 1~18. Use the following chart to identify the applicable replacement piston.
    • 1~5 uses "A" piston
    • 6~10 uses "B" piston
    • 11~15 uses "C" piston
    • 16~18 uses "D" piston
    http://www.pro-x.com/eng/oversizes.asp?No=01.2518

  3. #3
    Moderator OsideBill's Avatar
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    The size is in the manual the cylinders are .0xx over fill in the xx with the number stamped on the cylinder. ex: 80.006mm is a 6 stamped on the cylinder etc etc
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Moderator RX951's Avatar
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  5. #5
    billy's gpr's Avatar
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    probelm being 2 cylinders are 12 ,the other is 10,should i run different size pistons?? ,B & C size pro x pistons!!

  6. #6
    Moderator OsideBill's Avatar
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    Quote Originally Posted by billy gpr View Post
    probelm being 2 cylinders are 12 ,the other is 10,should i run different size pistons?? ,B & C size pro x pistons!!
    Yep!!

  7. #7
    billy's gpr's Avatar
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    Question

    what about engine balance???

  8. #8
    Moderator OsideBill's Avatar
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    Won't affect it Yamaha had different sizes in there to begin with. The size difference is miniscule we are talking less than .001" total difference between the four sizes. The thing to do is balance pistons anyways on any application, they should be within .1 grams of weight to each other. I have had three pro-x pistons same size weigh as much as 1.2 grams different from each other. I had some wisecoes that were 2.5 grams difference between the three. Best to have a shop do this it requires cutting inside the skirt on a lathe. if it is a small amount you can do it with a dremel.

  9. #9
    OLD # 7 IEGPR's Avatar
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    Whats the bigest piston ever used in an R motor??

  10. #10
    billy's gpr's Avatar
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    Quote Originally Posted by IEGPR View Post
    Whats the bigest piston ever used in an R motor??
    people are using 90mm,standard is 80mm

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