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1999 Ski Nautique - Vibration?

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  • 1999 Ski Nautique - Vibration?

    New to me '99 SNOB. Replaced the prop(old was dinged). Very difficult to remove, used puller, heat, and force w/ wood block and hammer. Eventually popped off, to find key rusted in prop. Installed new ACME 422. Took out and water tested(1st time) - fired right up, engine seems to run well. Boat has obvious vibration when applying throttle, vibration lessens a bit at speed.......is this a prop/driveshaft issue? Or possibly a rough running engine issue(GT-40).

    Driveshaft turns easily by hand when on trailer, very little play if any at all.
    While on lake, revved engine out of gear, sounded good.....thoughts?

    Should I start by replacing plugs, wires, distributor cap, and rotor or look into driveshaft issues? Thanks! Learned a lot on here already.

    Click image for larger version

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  • #2
    Could be a bent shaft, shaft to transmission alignment or worn cutlass bearings in the strut. Or, all three.

    Look at YouTube for videos on the topics listed above.

    It's not engine related if it is happening when under way using the propeller.

    Sent from my SM-J337V using Tapatalk

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    • #3
      Very likely that the prop isn’t correctly seated on the shaft. Google prop lapping and you’ll find a wealth of information. I always install props by lapping them to the shaft as it provides a smooth grip to the shaft and 100% surface contact. There is likely a video on the Acme propeller site as Acme recommends lapping on all of their props. A half hour job max.

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      • #4
        Experienced the same on mine, worn cutlass bearing was the culprit.

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        • #5
          Originally posted by DVskier View Post
          Very likely that the prop isn’t correctly seated on the shaft. Google prop lapping and you’ll find a wealth of information. I always install props by lapping them to the shaft as it provides a smooth grip to the shaft and 100% surface contact. There is likely a video on the Acme propeller site as Acme recommends lapping on all of their props. A half hour job max.
          I still don't get this. I'm not saying there's anything wrong with doing this, I just haven't seen any real evidence to show this makes a difference. The factory does not do this. My dealer does not do this. SURELY, if not lapping the prop on the shaft caused problems the factory and bigger dealers would be doing this by now?

          And I really don't believe this would cause vibration. Either the prop has a bend in a flute, it's out of balance, or something else in the drivetrain is out of whack.

          -Charles

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          • #6
            Charles you’re surely able to draw your own conclusions but Acme certainly recommends it. I have done this and it’s straightforward, just requires a bit of valve grinding compound and a bit of Prussian Blue. Your boat will certainly run smoother. By the way the key on the shaft has absolutely nothing to do with holding the prop on the shaft.
            But maybe you’re right and Acme is full of crap eh....?

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            • #7
              I’m pro-prop lap but the kind of vibration he is describing is not because of lack of prop lap. But it still could not be seated on the shaft right or the prop was somehow bad to begin with. Maybe try a different prop just to rule that out or try re installing it.
              Last edited by MTRBTR; 1 week ago.
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              • #8
                Thanks for all the help! I'll try a different prop as well as prop lapping.....see if that helps.

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                • #9
                  I
                  Originally posted by DVskier View Post
                  Charles you’re surely able to draw your own conclusions but Acme certainly recommends it. I have done this and it’s straightforward, just requires a bit of valve grinding compound and a bit of Prussian Blue. Your boat will certainly run smoother. By the way the key on the shaft has absolutely nothing to do with holding the prop on the shaft.
                  But maybe you’re right and Acme is full of crap eh....?
                  Well I never said "Acme is full of crap" or anything like that. I said: The factory doesn't do this. My dealer doesn't do this. I've never, ever seen any before/after that demonstrates how it makes the boat "run smoother" or eliminate vibration.

                  Again, I'm not saying there's anything wrong with doing it. If it makes you feel better, go right ahead. If it *really* made a difference, the factory would be doing it.

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