R90/6 cylinder over bore

Discussion in 'Airheads' started by arbalest, Oct 11, 2021.

  1. arbalest

    arbalest Long timer

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    Can R90/6 cylinders be bored to 94mm (R100 bore)?
    #1
  2. bmwrench

    bmwrench Long timer Supporter

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    Maybe, but the liner would be quite thin. What year is the engine?
    #2
  3. Beemerguru

    Beemerguru Beemerguru...G/S guy

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    You'll end up with the same experience as the 1050 kit sold at an independant BMW fab shop back in the '80s and '90s.

    Great for racing but ovaled out within a few thousand miles of touring..thin walls and heat don't mix for long.
    #3
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  4. Disston

    Disston ShadeTreeExpert Supporter

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    Not advised. You would end up paying for something that is not useable most times. Even if it works the liner will be so thin it may wear thru in a hundred miles or so.

    If you want bigger bores buy the kit or find some R100 cylinders with pistons that fit or can be made to fit. Used parts are a squeeze these days so smart money is on the kit.
    #4
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  5. arbalest

    arbalest Long timer

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    76
    #5
  6. Disston

    Disston ShadeTreeExpert Supporter

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    A 76 engine has the large bore case and is an easy swap to late model nicklesil cylinders and Pistons.
    #6
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  7. bmwrench

    bmwrench Long timer Supporter

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    Or two of these... PISTON.jpg
    #7
  8. arbalest

    arbalest Long timer

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    #8
  9. bmwrench

    bmwrench Long timer Supporter

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    The piston pictured is for '81 on R100. I have them for a variety of Airheads.
    #9