Engine to jet coupling

Discussion in 'Jet Drives' started by mikkijayne, Sep 7, 2016.

  1. mikkijayne
    Joined: Jul 2015
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    Location: UK

    mikkijayne Junior Member

    I was wondering about that exact point actually. The American jets are always used with V8s aren't they, with the exception of a few VW TDI conversions I know of. The PP jets though were often used with 4-cylinders (Pinto) so much more torque spiky than a V8 which may explain why the rubber donut coupling was used compared to the CV joint on the American ones.

    I'm fairly sure my jet came from a V8 setup hence the flange for the CV rather than the donut. I'm putting a V6 in so I guess it could go either way :D
     
  2. anthony goodson
    Joined: Mar 2007
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    anthony goodson Senior Member

    If your jet was originally a V8 set up ,it will have a four bladed impeller and a seven volute stator. The V6 and Pinto were 3 blade and 5 volute. Rubber donuts were originally used on all of them. As baeckmo said Metalastic only,never Hillman imp. This left very little flywheel clearance from the jet intake roof on the V8's,something you should check before designing your coupling.The depth of your Audi sump should be considered also .
     
  3. mikkijayne
    Joined: Jul 2015
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    mikkijayne Junior Member

    Yep thats it - 4 blade impeller and seven volute stator.

    If even the V8s had metalastic then I'm at a loss as to why mine came with a flange to fit a CV. I've not found a picture of this flange anywhere - only the ones for the metalastic. Not sure where I read Hillman Imp tbh, but a landrover UJ fits perfectly.

    I've checked flywheel clearance and thats tight but enough :) The sump on the Audi is at the front and designed to sit horizontal. Thats largely why I'm interested in a CV joint rather than metalastic (plus thats what I think it came with as above), so I can have a couple of degrees difference between the jet and the crank so the engine can sit level.
     
  4. CatrigCat
    Joined: Jul 2016
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    CatrigCat Junior Member

    If you use the above double cardan joint, try to keep the angle of the engine output shaft the same as the angle of the jet input shaft.
    This way any speed variation induced by the first U joint is cancelled by the second U joint and the double cardan joint acts almost like a constant velocity joint.

    The advantages of using a double cardan joint is that the engine can sit on a different plane than the jet and you can use soft engine mounts that allow the engine to vibrate without transmiting the vibration and noise to the hull.
     

  5. CatrigCat
    Joined: Jul 2016
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    CatrigCat Junior Member

    Only for really small transmissions.

    The transmissions used on V8s are big and robust enough that the engine torque fluctuation between 8, 6 or 4 cylinders doesn't matter.
     
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