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Clearance piston-cylinder

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fanfan26, Aug 10, 2018.

  1. Fanfan26

    Fanfan26

    Joined:
    Mar 14, 2012
    Hello,

    Thus it is necessary to rebore a cylinder for a marked piston 78mm by adding the clearance (0.11) = rebore 78.11mm or is he included in 78mm = rebore 78 mm ?
     
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  2. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    USUALLY the piston manufacturer will state the clearance necessary and the cylinder is bored to the appropriate dimension. The clearance given may vary depending on the use of the engine. The correct way to do this is to measure the piston diameter at the point specified by the piston manufacturer, then adding the necessary clearance and boring/honing the cylinder to that spec. Obviously the bore first has to be inspected/measured to ensure that sufficient boring is done to eliminate any taper in the bore and any scoring that may have occurred. Once it is determined what THAT minimum dimension is, a piston can be selected.

    For example, you may start out thinking a standard size piston would work but subsequent bore measurement determines that, to eliminate taper, the cylinder will have to be bored to a larger size.
     
  3. madass140

    madass140 VIP MEMBER

    Joined:
    Nov 6, 2011
    clearance is always on the piston.
     
  4. Fanfan26

    Fanfan26

    Joined:
    Mar 14, 2012
    Pistons are GPM marked 78, thus rebore in 78 mm, that's it.
     
  5. kommando

    kommando

    Joined:
    May 7, 2005
    Normally you hand over the barrel and piston to the borer shop with what clearance you want, they measure the piston and bore accordingly.
     
  6. concours

    concours VIP MEMBER

    Joined:
    Dec 29, 2011
    It bears repeating, to set up a new piston with original clearance, NOT “wear limits”, which are sometimes mentioned in repair manuals.
     
  7. Fanfan26

    Fanfan26

    Joined:
    Mar 14, 2012
    Thanks you very much for yours answers ;)
     
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