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1997 Seadoo GTX Low Compression

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  • 1997 Seadoo GTX Low Compression

    Hello Forum. Hoping for some direction. I bought this seadoo last year on kinda of a whim. Never even drove one before. And didn't check it out as good as I should have. It has the 787 engine.
    It ran great for a couple of hours (stopping, starting, ripping around) then just died and wouldn't start again. No sputter no nothing just died. Almost like it was shut down.
    Anyway. Assuming a fuel problem I rebuilt carbs and changed all the fuel lines and I don't remember what else. Never got it running. Then just forgot about it for the winter.
    Back to it today, I did a compression test. Front cylinder 130# back cylinder 60#. Both hold pressure if that means anything. I have pulled the cylinder cover off but nothing jumps out at me. Both pistons look to be in good shape. There is play in the front piston (130# compression) but no play in the rear. The rear piston appears clean while the front one is black. There is some minor scoring on rear cylinder wall.
    I am thinking piston rings on rear cylinder are not right. There is evidence of it being apart before.
    What do you guys think?
    Any input is appreciated.
    Thanks, Mike

  • #2
    Low compression means you lost half the power

    How is spark?

    Many time there is a lack of spark for the reason not running, but low compression is just compounding the issue
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

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    • #3
      Good spark. Or at least what I think is good. Had new plugs when I got it.

      Comment


      • #4
        Use a spark gap tester, this way you can tell if it does have good spark. Spark should be white or blue, and need to get the compression up first, so rings, valves or gasket
        94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
        95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
        07 Seadoo GTX
        Merc Adults Only VP Adults Only
        G-Dad always said "First Liar doesn't stand a chance"

        Comment


        • #5
          Thanks for the help.
          I have the top end apart. The cylinder with low compression had a piston ring jammed up. Didn’t move freely on the cylinder. Other that nothing jumps out. I am thinking new rings and all new gaskets as you suggested. What valves would should I be looking at ? Exhaust?

          Also found some sand in the water jacketing. Not sure how much yet. Any precautions or concerns with this?

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          • #6
            Not an expert with a doo, but fixed many of them. That said I would use what doo list, otherwise for better and more informed info, check out greenhulk.net, some real sharp guys over there
            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
            07 Seadoo GTX
            Merc Adults Only VP Adults Only
            G-Dad always said "First Liar doesn't stand a chance"

            Comment


            • #7
              Is the cylinder lining scored from the stuck ring ? If you’re lucky it will free off with oil. If you’re unlucky you’ve ran lean in that unit or the oil line to it is starved. Is it still oil injection ? They are one of the few seadoo 2 strokes that are generally reliable

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              • #8
                I assume the cylinder scoring is from the stuck ring. It really isn’t bad. I was able to free up the ring. Seems like there’s a pastry film on the rings. I think this has been apart before. I am going to clean, inspect and measure everything and go from there. I picked up a gasket kit today.
                yes it is still oil injected.
                i appreciate the help. Thanks

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                • #9
                  So it turns out I only freed up one ring. The second ring ended up breaking. It was jammed real good. I took both cylinders, pistons and rings to a local repair shop. They measured everything. Cylinder with low compression is out of round by however many thou. The other one checks good. They are going to hone the one cylinder and get new piston and rings. He said pistons are not original and are over sized by .005” ( I think ).
                  He recommended leaving the good cylinder and piston as is. So now waiting for parts and cylinder to be honed.
                  Thanks for the help. I will update when it’s back together. Hopefully this is it.

                  Comment


                  • #10
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                    Best bet is to just have it bored if it's out of round that bad. Both cyls really need to be the same bore. They were prob .5mm oversize which is .020. If one piston was clean, I would suspect water intrusion, maybe from a bad head gasket. Might check and make sure the heads and cyl's aren't warped or cracked.

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