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  1. #1

    Join Date
    Mar 2011
    Fallbrook, CA

    Polaris 750 Engine Swap Project Update

    Hi, just wanted to give a few updates on my polaris 750 and that will lead into my questions. I have swapped polaris motor with a 1990 yamaha 650 and naturally ran into a few problems. I am trying to figure out how the cooling works on the polaris, what pumps the water in? The black plastic box to which the water box connects to is for the exhaust gasses, but then what are the 2 hoses with another smaller box are for? I took the smaller box apart and not sure if thats the water pump, its loaded with a spring a thermostat and another plastic piece inside. Now as far as the jet pump goes what are those 3 lines inside the hull for? Two of the same size and a bigger one which seems like its sealed are they used for water delivery as well? I would appreciate of you guys can clarify that for me. Thanks!!!

  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Um, you are going to have some fun with that

    The cooling water supply is pressurized by the jet pump itself. There is no separate water pump for the engine. The cooling water comes in from the jet pump down low on the right side of the pump base inside the hull using a 3/4 inch hose.

    Also connected to the jet pump are two smaller diameter bilge siphon hoses. They should connect through plastic elbows then have metal mesh filters at the hose ends. The plastic elbows must be mounted up high inside the hull. When the jet pump is pumping water the siphon hoses have suction and draw any water in the bilge out.

    That 'box' with the thermostat is the thermostat housing, and it also has a pressure bypass valve (spring loaded).

    What model and year was this Polaris 750 before you made changes?

    Got any photos of how the Yamaha motor fits in the Polaris hull? How well does the drive shaft line up?

  3. #3

    Join Date
    Mar 2011
    Fallbrook, CA
    Polaris is a 93. Well that sounds bad... Any suggestions on how I can do this set up? The yamaha motor is as simple as one hose for water cooling (well 2 if I separate the muffler from the engine). And I will have even more fun getting the shaft connected to new motor because polaris just has this shaft that goes into the coupling and yamaha has this round coupler but I figured its still doable might have to do some welding though... Otherwise the engine did fit in very nicely Ill get some pics in the morning. Sorry about my ridiculous terminology for explaining jet ski parts it will be clear once I post the pictures. So far it has been a fun project and cooling is my biggest concern at this point so if you have got any suggestions on how to pull this off let me know.

    ---------- Post added at 03:04 AM ---------- Previous post was at 02:08 AM ----------

    I actually started looking at the polaris parts site and diagrams are helping out a lot, now at least i get an understanding how the cooling works and it looks like it can be done, my only question that remains in the "box", if I were to take it out of the scenario and just use one hose instead of two that would basically give the water and pressure to cool the yamaha motor. Am still missing a point here?

  4. #4
    john zigler's Avatar
    Join Date
    Aug 2006
    the yamaha 650 motor water inlet is down low on the exh manifold. the water goes in the motor here, comes up through the head, then connected to the pipe via a 3/8 hose. the water then goes in the pipe, is injected internally, and goes out the exh.

    it is really a very simple system. you will need to just adapt down the larger polaris 3/4 feed hose, to the smaller yamaha 3/8.

  5. #5

    Join Date
    Mar 2011
    Fallbrook, CA
    One more question, do you think I can get away with using Polaris water box or should be using Yamaha's?

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