Bad load related vibration
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Bad load related vibration

  1. #1
    Senior Master Technician
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    Default Bad load related vibration

    Hey, just restored a 79 Tahiti jet boat, its got a berkely drive and 454 chevy engine, im a Ford Senior Master Certified tech at a dealership and rebuilt the whole driveline myself, the motor runs awesome out of water and can turn to rev limiter no problem, when im in the water ill mat it and runs awesome untill im wide open for 30 sec or so, then i got a real bad vibration, (the engine actually jumps up and down), when i redid the jet drive i noticed the shaft near the bowl bearings was worn and i assumed that the problem may lye in there due to excessive slack between the shaft and bearings, when i removed the bown there was a bunch of water in it due to the heavy grooving were the seal rides on the shaft and the bearings were down to copper in some places, im thinking maybe the slack is causing the impeller to contact the wear ring and spin around like a unbalance washer, another possibilty is when i rebuilt the H bar using pto u joints it threw it out of balance, (but why is it ok out of the water?) its like its load related, any thoughts?

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  3. #2
    Senior Member motomattox's Avatar
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    IMO you would have a consistent vibration if it was in the driveline. I would look in the pump. Did you notice play in the shaft especially where you noticed the wear? It could be that when the pump is loaded with water and the bowl pressure rises your getting this issue. Verify that the shaft is true and straight (NO RUN OUT). It really sounds like you might have a bent shaft etc. I'm sure others on here can give better advice but either way it sounds like you already know you've got some pump issues....
    "Keep talking...it aint often I get to hear a genius speak"

  4. #3
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    Default vibration

    I would look at the pump first you will probably find the problem as soon as you take it apart. If the shaft is too badly worn it will be through the hard chrome on the end of the shaft.
    I would look at the thrust bearing as well.

    Good luck,

    Chris

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  6. #4
    Senior Member Brendellajet's Avatar
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    You don't want to be running that thing off the trailer, especially not up to the rev limiter, with the driveline attached.

    Id eliminate the variables and rebuild the pump completely and find a used shaft that is servicable since it sounds like yours is beat. There is a manual on the AT website with decent instructions.
    "He is a lover, not a fighter. But he's also a fighter, so dont get any ideas."

  7. #5
    Boat Nut sleekcrafter's Avatar
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    Sounds like excessive cavitation, either pump is fouled, clearances are wrong, or stuff is worn out.
    Upper Midwest Power Boat Association
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  8. #6
    Senior Member Futs's Avatar
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    Could also be the finger grate in the intake if thats what your running. They will vibrate at a certain speed. Check the pump out and if all is ok then check the intake grate asuming you have a finger grate.

    Some bowl bushings are already brass, so they will look brass.

  9. #7
    Prune-Picker
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    Quote Originally Posted by mikevoisine View Post
    ...when im in the water ill mat it and runs awesome untill im wide open for 30 sec or so, then i got a real bad vibration, (the engine actually jumps up and down)...
    Pump is starving for water. Get a loader!

    Cs

  10. #8
    Senior Member sleekvino's Avatar
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    i'd go with the last 2 post first, before ripping the pump apart.
    PORNO RACING INC WHERE ITS "HARD" TO WIN

  11. #9
    Senior Member ol guy's Avatar
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    Quote Originally Posted by Clockstart View Post
    Pump is starving for water. Get a loader!

    Cs
    Pull your'e hand hole cover and read it! If it doesn't tell you anything then paint it and go play in the water and check it again. Also when you launch is the boat in reverse for a fire and back off? If a pump is not loaded at launch properly you can catch an air pocket at the top of the bowl that is hell to "burp" out! This will and does create the vibration you are going thru, not to mention the hell it plays on the impeller shaft. M

  12. #10
    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by mikevoisine View Post
    the motor runs awesome out of water and can turn to rev limiter no problem
    Hello Mike and welcome !, some questions, have you run it "out of the water to the rev limiter" latley and/or before this problem occured and does it have a jetaway ?

    when im in the water ill mat it and runs awesome untill im wide open for 30 sec or so, then i got a real bad vibration, (the engine actually jumps up and down)
    Is this a one time occurance and you put it on the trailer or does it reoccur as you described with expirimentation?
    when i redid the jet drive i noticed the shaft near the bowl bearings was worn and i assumed that the problem may lye in there due to excessive slack between the shaft and bearings, when i removed the bowl there was a bunch of water in it due to the heavy grooving were the seal rides on the shaft and the bearings were down to copper in some places, im thinking maybe the slack is causing the impeller to contact the wear ring and spin around like a unbalance washer
    Safe to assume when you rebuilt the pump that you did you replaced the bowl bushings that were "to copper" and fixed the shaft ? (nominal allowable clearance between tail shaft and bushings is very skinny) ?

    another possibilty is when i rebuilt the H bar using pto u joints it threw it out of balance, (but why is it ok out of the water?) its like its load related, any thoughts?
    Typically Drive line wear between the pump shaft male splines and Drive line female splines ("machine noise") will manifest as a "stacato type "clunking noise" and lessen or disappear under an impeller load have you per chance rolled under the boat and taken a good look in the intake with a bright flash lite .... Tom

  13. #11
    Senior Member Cowboy_Mike's Avatar
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    If you roll under and take a look, look at your impellers leading edges. If it looks lik esome one sand blasted it, you could have the cavatation issue, and need a loader., or it could need to be freshened up Lots of variables to look at before doing that. If you pull the hand hole cover, see if you can stick your hand on the pump shaft and wiggle it. Could be a half dozen things, from packing, bearings, and bent shaft, to loading the pump properly at mid to top end. Heck, it could even be a bad surface on the bowl mounting flange. If you have droop, it could have air trapped in the pump with out a prim-a-jet. I am no tech, but there is several of them on this post that can answer your question better with more info. Did you rebiuld the pump, or just forward of the pump?

    Read the pumps impeller, hand hole cover, bowl oil, and shaft bearing grease. You should also take a look at the packing. 1 drip per minute. If you look at the AT web page, they will tell you how to do that part.

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