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Help needed on GP800 LE with bad compression

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  • Help needed on GP800 LE with bad compression

    I bought a 1998 GP800 used last year, and rather than bring it to my own mechanic, I called the owners mechanic who said he checked it out the year before and it was fine.

    Well, it has never started easily, and I had to use starter fluid to get it going. However, once it was running, it was generally fine, except seemed to run a little rough.

    Anyhow, at the end of the summer I tried to sell it. That guy did bring it to a dealer and they said the compression on the back cylinder was bad, and they would need to replace the whole motor for $2000. Well I ony paid $2500, so I wasn't ready to do that.

    Anyhow, I just checked the compression and sure enough, the front was 120 and the back was 60. However, it didn't ever start when the compression guage was on, so I don't know if that would affect anything.

    Anyhow, I need help trying to decide what to do.:emoticonb I have some mechanical knowledge, but not a ton. I would be willing to pay up to around $800 to fix the problem, but want it done right.

    Please help.

    I forgot to mention, the reason I was so trusting, was because the ski only had 72 hours on it. I'm an idiot!

    New update. I did finally get the ski started with a cheap $20 compression checking kit, and the back cylinder read 130 this time. I could not get it to start with it on the front cyliner yet tonight, but will try again tommorrow with more starting fluid. This time when I tried to start on the front the compression only went up to 90.
    Last edited by djtaylor; 04-20-2007, 09:39 PM. Reason: New compression check.

  • #2
    Re: Help needed on GP800 LE with bad compression

    http://www.sbtontheweb.com/Merchant2...gory_Code=62-4

    You could get away with just the top end kit above,as long as there are no metal shavings in the lower end...you will see this when you pull the cylinders.

    Now,you do not check compression with the motor running.Make sure you have the correct tip on your compression gauge...it should be as long as the threaded part on your plugs.With a fully charged battery,both spark plugs out and the plug wires grounded...turn the motor over just long enough to where the needle on the gauge doent go any higher....usually 6-7 turns. That will give you your compression reading. Do both cylinders,and see if it is what the dealer said it was.

    If so,I would recomend the topend kit above as long as there is no major damage to the cylinders that would have caused metal shavings or particals to get into the bearings on the crank. If you do see metal shavings,then you will need a new motor.Make sure you check your powervalves also.

    I would also recomend that you get a repair manual for your ski,it will help you understand alot more about these motors.

    http://www.sbtontheweb.com/Merchant2...gory_Code=40-4

    This includes all new powervalves as well.
    Visit www.pwctoday.com for techical help

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    • #3
      Re: Help needed on GP800 LE with bad compression

      I keep reading different things on the "how to check compression" thing in this forum. That is why I am so confused.

      Anyhow, I did it your way and came up with 90 and 60 respectively this time.

      If I am going to have to replace the engine anyhow, what is the harm of using the ski this season. The worst that can happen is that the engine freezes right?

      What I would really like to do is go the cheap route and replace the clyinder and sleeve, and just suck out any metal shavings if I find them. Would that work?

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      • #4
        Re: Help needed on GP800 LE with bad compression

        Unfortunatly,that will not work too well.

        'IF' there are metal shaving in the lower end,they are in places you cannot see,therefor you cannot remove them and they may have already done damage.

        The compression reading that you posted are both too low,and way out of spec...The max difference is 10% between the two cylinders.

        This is an expensive hobby/sport,and if you dont do things correctly,it gets more expensive. If you were to run it until it locks up or snaps a rod,you may be looking at more money due to not having a good core.
        Visit www.pwctoday.com for techical help

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        • #5
          Re: Help needed on GP800 LE with bad compression

          OK. I understand. I don't think I checked the compression correctly. I am going to give it a try again this weekend, making sure I first warm it up properly, then make sure the throttle is wide open when I try to turn it over with a new battery, and no spark plugs.


          Sorry this has been such a learning leason for me. If the compression is still bad, I will order a new engine and try to replace it myself. If I have problems, I have contacted a mechanic who will do the job for an extra $500.

          I do have a repair manual, but it is not overly informative on some aspects. For instance, how to I check to make sure my powervalves are functioning properly? I have been told by my dad that if the valves are not closing all the way that can reduce compression.

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          • #6
            Re: Help needed on GP800 LE with bad compression

            We wil help you get through the new motor.Even though $500 is not a bad deal as long as he knows what he is doing.

            The valves that your dad is talking about are different that the powervalves on a PWC.They are not intake and exhaust valve that close completly,so they will not affect compression testing.
            Visit www.pwctoday.com for techical help

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            • #7
              Re: Help needed on GP800 LE with bad compression

              Sounds good. Thanks alot for all the help. I will check compression again this weekend. If bad, then I will check the pistons and cylinders. Finally, I will check the motor for shavings. If there are shavings I will go with the new motor. If not, the I will do the cylinder exchange.

              With the Cylinder exchange do I have to send mine in first or can you send me the replacements and then I send mine in? I figure the latter will have a quicker turnaround on the bike.

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