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Thread: 86 w/ long rod.

  1. #11
    Member scrappy's Avatar
    Join Date
    Dec 2019
    2.5hrs East of the Oregon dunes
    Quote Originally Posted by moonboy274 View Post
    very true , one more question if my piston size reads 67.85mm I would need to buy a 68mm piston to replace it ????
    It depends on the condition of your current bore. If the cylinder is badly scored or out of round it will need to be bored & the next size up from 68mm (which would be 68.5mm) may be required.

  2. #12
    Senior Member acecarlos's Avatar
    Join Date
    May 2010
    Alta Loma, California
    Quote Originally Posted by moonboy274 View Post
    So my cylinder looks good no scratches or wear marks and my piston looked great besides the top. All I should have to do is hone the cylinder? If the piston that came out of it is 67.85mm the 68mm should slide right in correct?
    Yes and No...:-)

    I (BDT Motorsports) would never just run a hone into a bore that has any significant run time, others might or will. Reason being BDT won't is because you don't know what you have unless the bore is accurately 'miked' with a bore gauge. And then only hone to clean up if the resulting new honed bore meets maximum bore diameter specifications. If you have a Honda service manual, you will note Honda has diameter tolerances for bore to piston sizes. 99.99% of the time, if you pass a hone on a bore that has more than 3-5 hours of run time, it will not clean up within Bore Diameter specifications...even a 'slight' clean up hone.

    Best is to have your cylinder bore fully miked & inspected by a reputable machine shop or 2 stroke engine builder first, determine current bore size, and decide what to do based on measurements. Almost all the time you will need to go to the next bore size...in your case if you are at 68MM, the next standard bore would be 68.50MM...that will give you the correct & best results.

    american opel likes this.

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