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  1. #1

    Pro 785 Engine Swap?

    Hi Guys,

    Haven't been here in a while - just getting back into the sport.

    Two years ago I was riding my 00 Pro 785 that had about 60 hours on it. It was the first time out for the season and the engine was running the best I could ever remember - when all of a sudden at 7k rpm it began to shake violently. The oil pump appears to have failed wiping out the crank and middle cylinder.

    After I tore it down, I gave up on the 785 engine as the cost to do a full rebuild of the crank / re-plate the cylinders was not something I had the time or money for. Now I have this great condition hull sitting in my driveway less an engine.

    It would be interesting to do a swap for a new N/A 4ST engine like a STX-15, which would be costly and likely wouldn't fit well in the small compartment of the 785 hull. The other option I was considering was a Pro1200 transplant using a remanufactured engine. Either way some of the cost could be offset by a partial part out of the 785 engine pieces that survived.

    Any thoughts on either of these ideas? Has a 4ST swap ever been performed in a 785?
    How similar is the 1200 long block to the 785? I am handy with a milling machine and could easily fabricate adapters to fit the triple pipes to the 1200 cylinders.

    Appreciate any thoughts or feedback

  2. #2
    Banned User
    Join Date
    Jun 2010
    Milwaukee WI
    There is a guy here who just dropped a motor from a Kawi STX 15F into an Ultra 150 hull.

    If it was truly an oil pump failure it probably would have taken out all 3 cylinders not just one. Something else probably killed that cylinder.

  3. #3
    The cylinders all looked dry when I tore it down. The major damage was in the center cylinder which was partially seized and the connecting rod large end completely separated from the crank journal. Any ideas what else could have caused this?

    I'll take a look at the 150 - STX swap for some inspiration.

  4. #4
    If i knew,...I wouldn't ask sea-one's Avatar
    Join Date
    Aug 2009
    They always run the best before they screw the pooch

  5. #5
    Rasta Mon Condoms We Be Jammin!!!!! TxPro1200's Avatar
    Join Date
    Aug 2006
    switching out to another polaris motor could get expensive quick for ignition pasrts.i know randy built a twin domestic motor with race pipes and dropped it into a 785 hull.if you found a 780 setup that was good you could combine the two.nobodys done a rotax that i know of

  6. #6

    Join Date
    Aug 2006
    Homer Glen Il.
    i know some guys are putting kawi 1100's in the pro hulls

  7. #7
    ilovemyskidoo's Avatar
    Join Date
    Jun 2014
    Wayland ny
    Where you located? May just be better to sell the hole thing and find another ski

  8. #8
    RLACEMAN's Avatar
    Join Date
    Aug 2011
    Random Lake WI
    It might be much easier to put a 750 or 780 motor in there, there is a member or 2 that has put pro pipes on those motors, the fit should be easier & I think the ignition parts would be easier to adapt & those engines are not as pricy. Otherwise I think parting it out would be a good option, some of those parts are very valuable & hard to come by. The 4 stroke idea is nice, but would be better to start with an SLT hull, I don't think they would fit in the Pro hull.

  9. #9
    Quote Originally Posted by ilovemyskidoo View Post
    Where you located? May just be better to sell the hole thing and find another ski
    Located in South West CT. I just picked up a new Kawi STX-15F to replace the Pro785, but still want to try and do some type of swap in the future.

    I may just send the crank out for rebuild this summer and do a full refresh.

  10. #10
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    I'm in CT imo rebuild the 785.

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