1960 Lark II as parts source for 1964 40hp?

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  • November 15, 2016 at 12:03 am #5698
    amuller
    Participant

      I have a Johnson 40 hp 1964 and need a parts motor as the gearcase internals are rusted and want to remove the 5" extension.

      Have a line on a 1960 Lark II. Model # is 35520 which appears to be correct for this year and motor. From a pic it has the double wall leg and no extension.

      Would I be able to use the gearcase and drive shaft from this motor on a ’64?

      Thanks for any guidance.

      November 15, 2016 at 12:14 am #47465
      chris-p
      Participant

        Ive done so much swapping my memory is fuzzy, but I believe the drive shafts are the issue with that swap. If I remember correct, swapping the drive shaft will allow you to swap the gearcase. Everything else is fine. I cannot remember what was different, perhaps the length? Someone will chime in with exactly why.

        November 15, 2016 at 12:22 am #47466
        amuller
        Participant
          quote Chris_P:

          Ive done so much swapping my memory is fuzzy, but I believe the drive shafts are the issue with that swap. If I remember correct, swapping the drive shaft will allow you to swap the gearcase. Everything else is fine. I cannot remember what was different, perhaps the length? Someone will chime in with exactly why.

          Am I correct that this would have the small crank taper and the flywheel nut had to be highly torqued to stay on?

          I’ve seen some complex discussions of shaft differences on these big twin motors. Something about how the weigh of the shaft is supported/end play controlled? In my case I would probably want to use shaft and gearcase together to get a 20" transom motor.

          November 15, 2016 at 12:48 am #47468
          chris-p
          Participant

            Yes the 1960 Lark requires 105 ft/lbs torque on the flywheel nut. Different crank. Different top bearings.

            November 15, 2016 at 12:50 am #47469
            chris-p
            Participant

              A lot of guys think that the gearcases easily swap between any of the 40hp motors. But that is incorrect. There are quite a few minor changes throughout the years, shift rod lengths one of them. Not hard to make it work, but they are not all plug and play.

              November 15, 2016 at 1:46 am #47476
              vintin
              Participant
                quote Chris_P:

                Yes the 1960 Lark requires 105 ft/lbs torque on the flywheel nut. Different crank. Different top bearings.

                What year did OMC go from 3/4 inch to 1inch cranks on the 40hp?

                I though it was after 1960 but am not sure.

                November 15, 2016 at 2:25 am #47483
                frankr
                Participant

                  Larger cranks came out in 1962

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