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  1. #1

    Compression a little low on PTO cyl

    New to polaris. Just picked up a 96 SLX780. When I checked compression before purchase got 130, 130, 110 Mag-PTO(Harbor Freight Guage so numbers might be off but Mag is clearly more than 10% below others). Used this to negociate a good price and took it for a test ride. First time on a SLX780, but I would not have suspected any engine problems given the way it ran.

    So here's the question. Should I open up the cylinder and take a look? Run some Seafoam or Ringfree through it and see if the compression improves? Do something else?

    The ski was fresh out of winter storage and cold would this have an effect on the readings?

    I don't mind using search and looking through old threads but I didn't find the answers I'm looking for. Would appreciate any and all suggestions.

  2. #2
    ryandi2's Avatar
    Join Date
    Aug 2009
    conesus ny!
    how did you check compression?

    cold motor? throttle wide open? all plugs out? good battery putting over 10.6 v?

  3. #3


    thanks for responding and i tested it with all plugs out full throttle.

  4. #4
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Welcome to the Hulk.

    Try a retest after it is warmed up.

  5. #5
    ryandi2's Avatar
    Join Date
    Aug 2009
    conesus ny!
    whats the max rpms at full throttle?

    i would not put any additives like you have said in at all..

    you should go threw the fuel system and replace all lines. and also remove carbs and clean them up/ rebuild if you have too..

    but i would also open up the top end and check the pistons tops for damage and look at piston wash..

    post pictures as well

    make sure all head bolts are tight as well

  6. #6
    thx il pull the head tomorow and take some pics

  7. #7

    Warm up

    [LIST=1][/LIST. Thanks me and my son are going to put it in today and warm it up and then check the compression again if it doesn't change well post some pics

  8. #8


    Took the ski out today and it ran well but the compression was still low on PTO after. I removed the head and took the attached photos of the piston, cylinder, and gasket. There is no obvious damage anywhere. The top of the piston is in good shape with a uniform dark color except for 2 small areas that are clean. The cylinder walls have some shallow vertical grooves that you can feel with you fingernail. The gasket consists of 2 metal pieces riveted together there does not appear to be any kind of sealant or fiberous material present, head popped off with no effort required. The piston does have more side to side wiggle room than I would expect don't know if this is a problem or just indication of worn rings/ cylinder.

    Have a look and let me know what you think.
    Looks like I,m posting with my sons login

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  9. #9
    ryandi2's Avatar
    Join Date
    Aug 2009
    conesus ny!
    is there any way to get clearer pics of the cylinder wall

    what do you mean by piston side by side play? is this while its in the cylinder or is this with it off? if off it is normal for the piston to move side to side... its not ok to have play in the crank rod (you can have a little but not much at all).

    the cylinder does not look that bad.. but if you say there is suff marks that you can feel.. then thats can be part of the issue.. but you might be able to get away with a hone and new rings..

    but before you do that id wait till some one that knows the fugi motors a little better look at those gaskets..

  10. #10
    blegan's Avatar
    Join Date
    May 2008
    The pic. of the piston looks like it has the begining of a hole in top, or am I just seeing something thats not there.

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