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Thread: SL 780---

  1. #1

    SL 780---

    Just purchased myself a 1997 Polaris SL780 with really scorched pistons and the cylinders are ok but need to be honed out. If anybody has any suggestions how this happened and how to fix it from ever happening again I would truly Appreciate it Thanks

    I think it might be the oil injection is this possible and if so how do you delete it. I can mix the gas myself.
    PS the tops of the pistons are gone, all the way down to the rings, thats what i mean buy really scorched

  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Welcome to the Hulk

    Click the link below for a good start

    The more you read, and search, the more info you will find.

    Oil failure is possible, but not the likely cause. Clogged carbs or other weakness in the fuel system is the most common culprit, often aggravated by poor maintenance and other problems.

  3. #3


    What K447 said ,the oil pumps in our skis are one of the most reliable parts on them.THat said I bet it had 2 year old or better gas in it,was ridden full throttle across a 10 mile stretch running the best it ever had ,due to the fuel pre-igniting due to a octane level that had fallen to about 40 or less.Then poof,pop,ping,splat and so on,game over,really check the carbs,fuel line for coming apart inside and plugging carbs,and of course empty tank and always use fresh fuel after your rebuild.You better check cylinders for being out of round also,anytime they get that hot,you usually wind up boring them to get it right,(you dont have much meat on a 780)but hey you never know building an engine is the best part besides riding them>Marvin

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Welcome to the hulk Caterd.

    Some pics would be nice. They may help identify possible causes of the burn down.

    Lack of oil would most likely not deteriorate the piston domes. Detonation would.

    Maybe the previous owner had high compression heads added, and used low octane fuel.

    Maybe the fuel was insufficient and ate away at the pistons.

    Could be a few things. That's why pics would help.

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