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  1. #1
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    How to tell if a rubber bonded coupler is failing

    I am working on my friend's SLT 780 and there is an issue with the jet pump. When you try to accelerate, it feels as though something in the drive train is slipping, accompanied by a whirring like noise. I just removed the pump, and other than the stator bearings being full of water and kind of noisy, everything appears to be ok. There is no rubber coming out around the coupler as of yet. The ski would go, but only top out around 45 MPH while showing 6600 RPM on the MFD, which is slow for this ski. I have hit 52 on the MFD with this ski before. Does this sound like most likely the coupler?

    Bryan


  2. #2
    100 MILES OF HEAVEN AND I AM SMACK IN THE MIDDLE KEYZBUM's Avatar
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    Quote Originally Posted by BryanP View Post
    I am working on my friend's SLT 780 and there is an issue with the jet pump. When you try to accelerate, it feels as though something in the drive train is slipping, accompanied by a whirring like noise. I just removed the pump, and other than the stator bearings being full of water and kind of noisy, everything appears to be ok. There is no rubber coming out around the coupler as of yet. The ski would go, but only top out around 45 MPH while showing 6600 RPM on the MFD, which is slow for this ski. I have hit 52 on the MFD with this ski before. Does this sound like most likely the coupler?

    Bryan
    1 vote no !!!
    i would look more at the seal job in the pump shoe area...
    mattman-hiding out in Atlantis trying to play some roulette and win enough for a new yami crank

  3. #3
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    It makes a sound as if something is slipping, its not just an rpm rise without the accompanied acceleration. It sounds like I would think a slipping rubber part would sound.

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Have you seen this thread?

    When a rubber bonded drive shaft coupler goes bad

    When rubber slips it tends to smoke or at least get hot. After running this machine at WOT, shut it down and feel the rubber bonded coupler. Is it really hot? Then it is slipping.

    Sometimes it is hard to see any problem with the rubber, even though it is slipping. Doesn't always look 'bad'.

    Whirring noise usually means the splines are slipping, either engine or impeller end.

    However, if the bearings in the jet pump are failing (water+steel=rust) that can make a similar whirring noise.

    Jet pump seal leakage tends to affect acceleration more than top speed. Once the hull gets moving, the intake water pressurizes the pump ahead of the impeller, so leaks just allow some water out of the pump, rather than allowing air into the pump (which would be ventilation at low speeds).

    Impeller blades in good condition? No dings or bent sections.

  5. #5
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    Jet pump bearings are bad. The whole housing was full of water when I removed the tail cone. Drive shaft seals need to be replaced. The impeller is pretty dinged up as well. The leading edges of the stator blades are dinged up but I think that can be cleaned up with a dremel tool and a file. The ski just didn't accelerate like normal and lost some top end, and this seemed to happen all of a sudden this year. The coupler appears ok but I'm just wondering if its possible for it to be bad. There was no burning rubber smell at all when the ski was running

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by BryanP View Post
    Jet pump bearings are bad. The whole housing was full of water when I removed the tail cone...

    The impeller is pretty dinged up as well. The leading edges of the stator blades are dinged up but I think that can be cleaned up with a Dremel tool and a file...
    Also check the clearance between impeller blades and the wear ring. Should be well under .020 inches clearance all around.

    Bad pump bearings can allow the blades to rub against the wear ring and grinds the blades down.

    If there is more than about 10 thousands blade clearance consider having the impeller refurbished if you decide to continue using it. Refurb costs about $25 plus shipping at SBT, and similar at Impros.

  7. #7
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    Impeller clearance was measured at .017 which isn't too good. I will recommend he gets it refurbed. I think we will fix all these issues and see how it works before we mess with the coupler.

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