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  1. #1

    Coupling question, Polaris engine to Yamaha jet pump

    I am building a jet boat and am trying to figure out how I can couple a 1200 Polaris to a gp1200 pump.

    From what i have read, the Yamahas are threaded, I assume the crank shaft is threaded. the Polaris has a splined end, my thought is to cut the Polaris shaft and thread it for the coupler. the issue is the splined end will only be held in place by the coupler.

    Do you think this will work? if not do you have any suggestions?

    Thanks
    Carlton
    Last edited by K447; 09-01-2019 at 10:03 AM.

  2. #2
    Click avatar for tech links/info K447's Avatar
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    I am not sure what you are proposing, but I can say the Polaris engine crankshaft end is threaded. The Polaris driveshaft coupler is threaded onto the crank end and the splined driveshaft then slides into the coupler.

  3. #3
    Quote Originally Posted by K447 View Post
    I am not sure what you are proposing, but I can say the Polaris engine crankshaft end is threaded. The Polaris driveshaft coupler is threaded onto the crank end and the splined driveshaft then slides into the coupler.
    I havent pulled the motor yet, next on my list. There is a rubber boot that the splines shaft runs through, I assumed the crank was splined. So if the crank is threaded then it should be fairly easy.

  4. #4
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Beachcustoms View Post
    I havent pulled the motor yet, next on my list.

    There is a rubber boot that the splines shaft runs through ...
    If you want to remove the coupler from the Polaris engine, do that before you unbolt the engine from the hull.

    Sometimes the Polaris driveshaft coupler needs quite a jolt of torque to loosen from the crankshaft. With the engine out of the hull it can be challenging to find a way to hold the engine in place while applying torque to loosen the coupler.

    With the engine still bolted into the hull, use the ‘rope trick’ to hold the PTO piston in place, then use a hefty wrench to loosen the coupler from the crank end. Sometimes the coupler lets go without a fight, sometimes.

  5. #5
    Quote Originally Posted by K447 View Post
    If you want to remove the coupler from the Polaris engine, do that before you unbolt the engine from the hull.

    Sometimes the Polaris driveshaft coupler needs quite a jolt of torque to loosen from the crankshaft. With the engine out of the hull it can be challenging to find a way to hold the engine in place while applying torque to loosen the coupler.

    With the engine still bolted into the hull, use the ‘rope trick’ to hold the PTO piston in place, then use a hefty wrench to loosen the coupler from the crank end. Sometimes the coupler lets go without a fight, sometimes.
    Thanks for the help, another question. Are the threads on the crank the same for each Polaris engine regardless of size? The shaft on the Polaris is 20 mm and the shaft on the gp pump looks to be 18mm. If I could find a coupler for the Polaris that had the same spline size as the GP pump that would make my life much easier.


  6. #6
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Beachcustoms View Post
    ... Are the threads on the crank the same for each Polaris engine regardless of size? ...
    Yes, as far as I know.

    Driveshaft spline diameters for Polaris are also all the same, on the models that use a splined driveshaft coupler.

    Note that Polaris did use a rubber finger style coupler on the MSX models.
    Same thread on the engine side as the spline couplers. I forget what thread the driveshaft side has.


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