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  1. #1

    Asking for help SL 780 1996

    I have a 1996 SL 780 that the back cylinder has burned up twice now. I've had it fixed twice by shops and it has happened within a few hours of the repair each year. It's getting real expensive as I live in Florida but have the machine in New York, so I have had it fixed late in the Fall and by the time I get it in the water in the spring or summer and it goes, the shop wants nothing to do with it!

    My brother will and can fix it, he wants me to I can get a whole cylinder and send to him to replace it. He says the one in there now has been honed to 50 thousands and doesn't think we should go any further? he also suspects the back seal as maybe letting air in? Anyone have any experience with this? He said someone here might know if the 750 cylinder can be used, apparrently he sees a lot of them available?

    Any suggestions would be great...Thanks


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    Get your brother to join up here, so he can directly communicate with the group.

    It sounds like the shop that did the work did not bother to fix the cause of the engine failures.

    My guess is that the carbs need to be rebuilt, and the fuel system freshened with new hoses, etc.

    The engine seals can be pressure or vacuum tested for leaks. The method is outlined in the Technical section here.

    Click below for the Polaris Service manuals, and lots of other good info.

    Also have a look here;
    Polaris Fuji (blue) engine

    The cylinders can be bored larger without trouble, as long as the port edges are rounded off properly, and the appropriate sized pistons are installed.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Welcome to the Hulk Keywest.

    It may be a bad rear crank seal, or another fuel related problem as mentioned above.

    A leak down test will tell if the crank seal is leaking air. I suggest doing this test after the engine is rebuilt.

    A 750 cyl can be used on that 780 case, but cannot be intermixed with 780 cyls.

    They use a different exhaust manifold between the 2.

    You can go larger than a .5mm (not 50 thous), but you'll want to do all 3 cyls if you do.

  4. #4
    Thanks so much for the input. My brother said the same about the test and if we were to bore out this cylinder anymore. Interesting that we can use a 750, if we change all three, that could be handy.

    Thanks for the help!

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    FYI: the 780 makes 12 more HP than a 750.

    So you may want to get a differenet 780 cyl.

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