66 427 vs 65 396 CrankShaft - NCRS Discussion Boards

66 427 vs 65 396 CrankShaft

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  • Peter M.
    Very Frequent User
    • February 1, 1984
    • 361

    66 427 vs 65 396 CrankShaft

    I understand that original GM 1965 396 and 1966 427 cranks had the same part number #6223 but were balanced differently due to the lighter rotating mass of the 396. If this is correct, was the visual difference between the cranks only the number and size of the drill holes or was a counterbalance weight actually cast wider or thinner depending on application.
  • Clem Z.
    Expired
    • January 1, 2006
    • 9427

    #2
    Re: 66 427 vs 65 396 CrankShaft

    unless the crank is brand new it could have been rebalanced for any comb of pistons and rods. the best bet is to take it to a good auto machine shop and have them balance the whole assy. this is the best $150 you can spend on any engine

    Comment

    • Duke W.
      Beyond Control Poster
      • January 1, 1993
      • 15610

      #3
      Re: 66 427 vs 65 396 CrankShaft

      The two large balance masses at each end of the crank are a partial function of reciprocating weight, which includes the pistons, pins, rings, and top half of the rod. They balance out the primary rocking couple that is generated from the reciprocating mass. Since both the 396 and 427 have the same stroke, the cranks can be machined from the same forging and be completely interchangeable, but the 396 pistons are likely lighter due to the smaller bore, so slightly lighter end masses would be be necessary for precise balance.

      If you don't know what you have, rebalancing the entire rotating/reciprocating mass would be required and, like Clem said, it's the best 150 bucks you can spend on any rebuild.

      Duke

      Comment

      • Peter M.
        Very Frequent User
        • February 1, 1984
        • 361

        #4
        Thanks Guys *NM*

        Comment

        • Mike Cobine

          #5
          Re: Thanks Guys

          While you are doing the balance work, have them balance the flywheel and clutch, too. You'd be surprised at how far off a clutch and flywheel can be, even new.

          Comment

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