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  1. #1
    Newb : ( JJLee138's Avatar
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    Looking at a used XP Tomorrow (Compression check question)

    I'm driving 2-3 hours to look at a used 96 XP that a guy said he'd sell me for $1800. He said everything works perfectly etc and it's nice and clean. Also had no problems letting me take it out on the water.

    Well I'm not much of a mechanic. Hell, all I've ever done in my life to an engine is change plugs and oil... I've been doing my homework on the boards for a couple weeks straight now and know that checking compression is important. So.... What tools do I need to do this. Where can they be purchased. What is the procedure for this. What kind of compression should I be looking for/expecting. And finally! Any thing else I should look for/at before taking this bad boy home?

    I know I'm asking a lot of questions here, but this is all so new to me Thanks a TON for your help guys. Hope I can return the favor some day.


  2. #2
    rick xp's Avatar
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    Just go and buy a spark plug socket and ratchet and a compression tester. Remove the spark plug, screw in compression tester.

    Hold the throttle wide open and crank the engine over using the starter. You should see readings in the 100's depending on condition, head work, etc.

    Just make sure both cylinders are even in compression. If there was a more than a 10 PSI difference in the cylinders i personally would start walking.

  3. #3
    Newb : ( JJLee138's Avatar
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    Quote Originally Posted by rick xp View Post
    Just go and buy a spark plug socket and ratchet and a compression tester. Remove the spark plug, screw in compression tester.

    Hold the throttle wide open and crank the engine over using the starter. You should see readings in the 100's depending on condition, head work, etc.

    Just make sure both cylinders are even in compression. If there was a more than a 10 PSI difference in the cylinders i personally would start walking.
    What size thread would I need on that adapter? Assuming there is more than one size? Like I said, bit of a newb here lol

  4. #4
    flyin' the friendly skies airbornexp's Avatar
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    there are two sizes for the compression tester. I got a cheapie from auto zone ans it has both adapters. the bigger one screws on to the smaller one that is built in to the line of the gauge. I think that a stock XP has about 150-155 PSI in each cylinder. like posted previously. if there is 10PSI difference id walk or buy and rebuild the top end for about +/- $350 yourself. its not that hard of a job. If you dont take it, PM me. Im looking for a ski like that one.

  5. #5
    Newb : ( JJLee138's Avatar
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    Quote Originally Posted by airbornexp View Post
    there are two sizes for the compression tester. I got a cheapie from auto zone ans it has both adapters. the bigger one screws on to the smaller one that is built in to the line of the gauge. I think that a stock XP has about 150-155 PSI in each cylinder. like posted previously. if there is 10PSI difference id walk or buy and rebuild the top end for about +/- $350 yourself. its not that hard of a job. If you dont take it, PM me. Im looking for a ski like that one.
    Thank you for the info man. My father in law had the exact tester you described with the two sizes, one inside the other, and also another one he gave me with just a rubber stopper on the end like a cork.... Is it important to test WOT?

    I'm checking it out tomorrow night and will let you know if I pass on it. If anyone else has any general advice on what to test/ look for while I'm on it let me know. Thanks!
    Last edited by JJLee138; 07-24-2008 at 08:01 PM.

  6. #6
    A WOT compression test should be the way it gets done because you want the maximum amount of fuel/air charge going in to give you a little more accurate of a reading. But I have done plenty of compression tests without touching the throttle and it was virtually the same. Take your time checking it over...don't let the guy rush you. If he's in a rush, it could be that he knows of something wrong and just wants to push it out the door. Test the compression both ways just to see if there's a difference. It's only a matter of rolling it over a few times with the starter, touching the air release tab and doing it again...shouldn't take longer then 15 seconds. One thing wasn't mentioned, pull the plug caps off before doing the compression test

    Check the bottom of the hull for any gouges. If there are some good ones there could be internal cracks bad enough to let water seep into the lower half of the hull. You would never see this in the engine compartment because it is considered as a laminated hull which means basically an external bottom shell and an internal bottom shell.

    Check the wear ring at the impeller as well. If it is worn out you will be hitting the rev limitter everytime you run it past 3/4 throttle. That could shorten the life of the engine if it's been run like that for long periods of time since they don't rev that high under normal conditions. If you can see more than a very fine line of light between the impeller and wear ring, it is either due for replacement or overdue depending on the gap. I have attached a pic of mine to give you an idea of what is overdue. This is looking straight into the impeller from the jet-pump nozzle. I used a utility light to highlight the airspace but a flashlight will do alright as well. There should be very little light between the rounded edges of the impeller blades and walls of the wear ring. With mine you can see there is quite a lot of space between this area. It is common to replace these once every year or two depending on where you ride and launch...hence the name wear ring but it is just another expense for you if he hasn't stayed on top of the maintenance end.

    Lastly, if the ski doesn't fire up from a dead battery...make sure he either charges it or puts in a new one. The reason being that you want to hear the two chirps when you plug in the lanyard. They are short and even as soon as you plug in. If you get anything other than a "chirp chirp" There are electrical issues which could get costly. Oh yes...one more thing...when you have the seat off...look at the purple part of the exhaust, you will see a bunch of welded circle spots. Have a look at them for any scratches, mine took a little ding and now it sprays water out of there. I haven't fixed it yet but plan on getting it brazed to get me by until my new pipe arrives
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    Last edited by Schwarzenegger; 07-24-2008 at 09:19 PM.

  7. #7
    Newb : ( JJLee138's Avatar
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    Quote Originally Posted by Schwarzenegger View Post
    A WOT compression test should be the way it gets done because you want the maximum amount of fuel/air charge going in to give you a little more accurate of a reading. But I have done plenty of compression tests without touching the throttle and it was virtually the same. Take your time checking it over...don't let the guy rush you. If he's in a rush, it could be that he knows of something wrong and just wants to push it out the door. Test the compression both ways just to see if there's a difference. It's only a matter of rolling it over a few times with the starter, touching the air release tab and doing it again...shouldn't take longer then 15 seconds. One thing wasn't mentioned, pull the plug caps off before doing the compression test

    Check the bottom of the hull for any gouges. If there are some good ones there could be internal cracks bad enough to let water seep into the lower half of the hull. You would never see this in the engine compartment because it is considered as a laminated hull which means basically an external bottom shell and an internal bottom shell.

    Check the wear ring at the impeller as well. If it is worn out you will be hitting the rev limitter everytime you run it past 3/4 throttle. That could shorten the life of the engine if it's been run like that for long periods of time since they don't rev that high under normal conditions. If you can see more than a very fine line of light between the impeller and wear ring, it is either due for replacement or overdue depending on the gap. I have attached a pic of mine to give you an idea of what is overdue. This is looking straight into the impeller from the jet-pump nozzle. I used a utility light to highlight the airspace but a flashlight will do alright as well. There should be very little light between the rounded edges of the impeller blades and walls of the wear ring. With mine you can see there is quite a lot of space between this area. It is common to replace these once every year or two depending on where you ride and launch...hence the name wear ring but it is just another expense for you if he hasn't stayed on top of the maintenance end.

    Lastly, if the ski doesn't fire up from a dead battery...make sure he either charges it or puts in a new one. The reason being that you want to hear the two chirps when you plug in the lanyard. They are short and even as soon as you plug in. If you get anything other than a "chirp chirp" There are electrical issues which could get costly. Oh yes...one more thing...when you have the seat off...look at the purple part of the exhaust, you will see a bunch of welded circle spots. Have a look at them for any scratches, mine took a little ding and now it sprays water out of there. I haven't fixed it yet but plan on getting it brazed to get me by until my new pipe arrives
    Thanks a ton for all that info man. The pictures are very helpful as well. I've read about the impeller and wear ring plenty, but actually getting a look at them did more than reading for weeks. Just to be clear I'm hoping for a gap that large or smaller than that picture if he's been on top of things(meaning that pic you posted is of a worn ring?) ? Now what angle am I seeing in that pic of the impeller and wear ring? Where do you shine the light into? Think that's my last question lol. Once again, thanks a ton for the write up bro.
    Last edited by JJLee138; 07-24-2008 at 10:47 PM.

  8. #8
    rick xp's Avatar
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    Just have a look in the end of the pump and get under the ski and have a look through the intake grate.

  9. #9
    Shine the light up inside the intake grate towards the back of the ski. It's under the ski where the propshaft leaves the hull. With the light being in there, go to the back of the ski and look into the pump nozzle, you will easily see what you're looking for when you see it. As for the gap...you want a lot less space/light to be seen between the impeller edges and the walls of the wear ring. Mine is worn out really badly so you're looking for much less light around the impeller than what mine shows . The reason for the wearing out is because of debris getting caught in there and spun around with the impeller before it leaves. You'll do pretty good when you go over it and if it's mechanically sound...you will love it. They're one of Sea-Doo's more relaible skis from what my friends have told me and what I have heard on here. I've only had mine for 3 years but I won't be getting rid of it.

  10. #10
    Newb : ( JJLee138's Avatar
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    Okie doke, I feel confident that I'm at least somewhat compotent to tell what shape this ski is in now. Thanks again for sharing some of your knowledge with me. Y'all have a free beer coming your way next time you're in the Indianapolis area : )

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