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  1. #1

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    ProX pistons for 15F / Ultra LX

    ProX makes 3 different size pistons for the 15F motors. One is standard bore, one is .01MM over and one is .02MM over. All 3 kits include the same stock bore rings.


    What's the purpose of the slightly larger pistons? The .01MM increments are so little (thinner than a sheet of paper) that you probably wouldn't be able to tell them apart without a micrometer.


    Does the Nikasil plating wear down slightly over time, which would necessitate the slight increase in diameter? For a rebuild, would it be better to use something other than stock bore? Any problem with using the .01MM over pistons if I can get them at a better price than stock bore?


  2. #2
    My guess, assuming that isnt a typo on their part and meant o say .01 inches, is selective fit like gpr pistons. Perhaps it's to accommodate not sending pistons with the cylinder when replating?

    Honestly I would throw the bore gauge on your cylinder (preferably torqued to the case with a deck plate) and see where you are at.

    In lieu of a bore gauge and all that jazz order one of the cheap ones and check the fit. If your cylinder has been run and not replated your are likely well within tolerance.

  3. #3

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    Don't think it's a typo... listed as 82.95MM, 82.96MM and 82.97MM.

  4. #4
    Take the time to smile sirbreaksalot's Avatar
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    Optional size pistons are for those that want to build a correctly clearanced engine...... rather than just slapping it together at close enough is good enough syndrome.... the rings are always filed to suit application......

  5. #5

  6. #6

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    I guess the Nikasil does wear down.

    Just took a look at the service manual and it mentions cylinder wear and a service limit.

    Interesting that ProX are the only pistons with these variants. Other brands have .25MM and .5MM over.

  7. #7
    steve45's Avatar
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    .01 mm = .00039" That's no much.

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