Engine gear box

Discussion in 'DIY Marinizing' started by Guest, Jul 11, 2004.

  1. Guest

    Guest Guest

    Hi there, just wondering if anyone can help me. I am looking at putting a 350 chevy engine in a ski boat. It has been maranised but was run in a jet unit so I am getting it back to the flywheel. I want a direct drive through to the prop. Would I need some sort of gear box on the motor before the shaft and if so would sort of ratio would be good. If not what else could I do.
    Thanx
     
  2. Black Swan
    Joined: Jul 2004
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    Location: Mission, B.C. Canada

    Black Swan Junior Member

    Most "tounament" style ski boats run direct drive from flywheel through a forward/neutral/reverse transmission. The most common of these would probably be the Borg Warner 72C, readily available. Gear reduction is not a necessity, just prop the unit appropriately for your boat. Lots of information available, just visit a tourney boat dealer. Don't forget to pay attention to the skegs, struts, stuffing boxes, rudder/steering systems and control and cable systems.
     
  3. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    I'll second that. I've got two of them (1.91:1 reduction) that are older than dirt and still going strong (knocking on wood) :D
     
  4. lots_of_knots
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    lots_of_knots New Member

    slow running and acceleration will be much smoother with some kind of reduction gearbox :D
     
  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If you put a flywheel, it will need a new harmonic balancer to match.
     
  6. Black Swan
    Joined: Jul 2004
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    Black Swan Junior Member

    Ski boats are rarely challenged with the need to run slow. Mostly you are looking for a good quick smooth acceleration to 30MPH and the ability to hold that speed while the skier flails around on the end of a rope. If the engine was properly "marinized" the proper flywheel and harmonic balacer should already be there. You may have to get a new "flex plate" which bolts to the flywheel and has the splined centre adaptor which then mates to the splined shaft of the transmission.

    If you're propped right, you should achieve your target speed with the 350 running around 3200 to 3600 RPM. This puts the engine in a good torque range and is a good place for the kind of "fingertip" throttle control that's needed for tournament type skiing.
     
  7. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    These are readily available on the 'net. Just search for borg warner drive plate (assuming you go with a velvet drive) and you'll get a lot of returns.
     
  8. lots_of_knots
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    lots_of_knots New Member

    i thought all engines required a harmonic balancer to smooth out crank vibrations caused by the crank webs winding then springing back during every power stroke, at the least a new one should be fitted and checked regularly
     
  9. Jets
    Joined: Jul 2004
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    Jets Junior Member

    I have an Olds V6 from an '85 cutlass (rear drive. The engine was balanced at the factory internally for a flex plate and no harmonic balancer (automatic). I have read elsewhere on the net that I cannot change to a real flywheel because of the method of balancing.
     
  10. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    If the engine is internally balanced then they didn't use the flywheel to counterbalance the crank, pistons, etc. In that case you can change to another flywheel with a matching harmonic balancer.
     
  11. Jets
    Joined: Jul 2004
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    Jets Junior Member

    Apparently not because they remove material on the crank to achieve balance with the flex plate and/or flywheel - harmonic in place. It is not a memorable motor, this Olds V-6. It is a 90 degree block with offset crank journals and un-ajustable valve train. It was cheap. I put in a cam to make about 150 hp and it is in a 13.5 ft 1961 Glasspar G3 hooked to a cog belt driving a surface piercing prop through the transom. I am still trying to get a good prop.
     

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  12. decay21450

    decay21450 Guest

    love the g-3's. anybody ever repower with a merc sportjet or omc turbojet?
     
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