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Crankpin Location at Top Dead Center

Discussion in 'Norton Commando Motorcycles (Classic)' started by Dukester, Jun 19, 2005.

  1. Dukester


    Jun 11, 2005
    Hello to All!

    I have a question about crankshaft rotation, specifically the reference point of the crankpin (timing/right side, #1 piston) when the piston is at top dead center.

    As the barrel is not directly above the crank/case at 12 o' clock like earlier singles/twins, what is the crankpin location when the piston is at top dead center?

    When piston #1 fires what is the location of the crankpin?

  2. Jason Curtiss

    Jason Curtiss

    Jun 14, 2003
    If the cylinder is canted 10 degrees from vertical, the crank pin will also be at 10 degrees when the piston is at the top of its stroke, or TDC.

    Now, when the engine is running, the ignition system triggers the spark plug to fire at 28 degrees before the piston and its crank pin reach TDC. This advanced ignition gives the air/fuel mixture time to burn.

  3. Dukester


    Jun 11, 2005
    Thanks Jason! :D
  4. nbmBruce


    Jun 3, 2005
    Or one could say (applies to any engine with straight connecting rods): When the centerpoint of the crankpin axis lines up with the line formed by the centerpoint of the crankshaft axis and the centerpoint of the wrist pin axis, that is the exact TDC.
  5. panic


    Sep 20, 2005
    Unless the pistons have offset pins, or the cylinder axis is offset from the crank center, or both.

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