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Thread: Piston to wall clearance question

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    Default Piston to wall clearance question

    I'm having an early Merc triple bored out .030 over and need to tell my boring dude what clearance I want.

    Looked in my genuine Merc manual and couldn't find it. Anyone have a spec?

    Thanks,

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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    Quote Originally Posted by Fastjeff57 View Post
    I'm having an early Merc triple bored out .030 over and need to tell my boring dude what clearance I want.

    Looked in my genuine Merc manual and couldn't find it. Anyone have a spec?

    Thanks,

    Jeff
    if pistons are stock you add 030 to original bore size

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    BoatRacingFacts VIP Aeroliner's Avatar
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    Quote Originally Posted by Fastjeff57 View Post
    I'm having an early Merc triple bored out .030 over and need to tell my boring dude what clearance I want.

    Looked in my genuine Merc manual and couldn't find it. Anyone have a spec?

    Thanks,

    Jeff
    The new Wisco pistons I now stock for the 20, 40 and 60 cubic inch engine call for .0065 clearance. I also use that with my merc pistons we run in D mod
    Thanks hydrospeed77 thanked for this post

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    Thanks. I guess a little loose is best for racing.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington
    Thanks Fast Fred thanked for this post

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    FFX-61
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    factory is about .004 on cast pistons, a forged piston is going to grow more than the cast bullet when at running temp, so more clearance is needed, about .008

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

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    Thanks!

    Happy Thanksgiving to all!

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

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