1956 Scott Atwater 7.5 hp Bail-a-matic gearcase

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  • January 19, 2021 at 8:50 pm #228206
    Buccaneer
    Participant

      US Member

      Nothing in the manual I have mentioned anything about adjusting backlash
      on this gearcase. It’s impossible the way it’s designed to hold the propshaft
      and turn the driveshaft to get a feel for the backlash.

      Only the shift dog between the two driveshaft gears is splined.
      The gears are bushed and rotate freely.

      The only indication on backlash seems to be what vertical movement
      (up and down) I have on the driveshaft. It does have noticeable movement
      up and down, and when you turn the driveshaft while it’s in gear, the
      gear mesh seems rather rough. If you hold up on the driveshaft while
      turning, it’s okay. I have no lube in the gear case yet.

      There was no shims in the gear case, and removeable thrust washers.
      The gasket between the gear case and prop shaft housing is pretty thin.

      Thoughts?

      DSCN0233

      DSCN0234

      Prepare to be boarded!

      January 19, 2021 at 10:15 pm #228216
      Mumbles
      Participant

        The roughness you’re feeling while turning the driveshaft is probably because the forward (upper) gear is riding low on the prop shaft gear and the gears are fully meshed. When power is applied, the forward gear will be forced upwards separating the gears a bit. The manual mentions that the driveshaft can be forced upwards to and if the impeller isn’t free to slide up and down on its drive pin, the impeller can be forced up against its housing, breaking the seal on its lower side. I think you are OK with them and when the lube is added, you wont notice it as much.

        These straight cut bevel gears are similar to spider gears in a vehicles rear end. When a rear end has limited slip clutches in it, the spiders spread under load causing the clutch packs to lock up.

        January 19, 2021 at 11:01 pm #228222
        Buccaneer
        Participant

          US Member

          Thanks Mumbles. I kind of figured centrifugal force would throw the gears
          apart and raise the driveshaft up. Guess I won’t worry too much about the
          actual gear mesh depth……… grease is a wonderful thing!

          Prepare to be boarded!

          January 21, 2021 at 5:40 am #228351
          billw
          Participant

            US Member - 2 Years

            When checking backlash on Mercruisers, an old trick was to apply pressure to the shift mechanism in such a way that the gear in question and the clutch dog purposely didn’t engage the ramps fully. In other words, you’d hold pressure on the shift with the clutch ramps touching each other at the top. This would lightly “lock” the gear from turning. Then, you’d pull up on the drive shaft and lightly rock it back and forth, and check the lash. It seems like you could use that method on the Scott case, but just pull out on the prop shaft and rock it, instead.

            Long live American manufacturing!

            • This reply was modified 3 years, 3 months ago by billw.
            January 21, 2021 at 9:23 am #228358
            Buccaneer
            Participant

              US Member

              Bill, I’ll play around with it a little more before I add lube to the gear case.
              I’m hesitant about having to pull the driveshaft back out at this point
              if need…… too much work getting time impeller installed, lol.
              Thanks.

              Prepare to be boarded!

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