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  1. #1
    Ryguy425425's Avatar
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    Relationship between hours on engine and compression

    I bought a '97 GTX last weekend for what I consider a good price. The only problem is that the seller had only owned it for a year, and didn't know the history at all. The hourmeter on the ski reads just under 320 hours, but the compression test read close to 160 PSI in both cylinders. Knowing I didn't use a very expensive meter, that probably wasn't very accurate, I figure the absolute least I could have is 140 PSI. I'm suspecting the top end has been rebuilt, but would those compression numbers match up with the hours?

    If a few people with 787s (or any other engine for that matter) could post their numbers the last time they did a compression test, as well as the number of hours on their engine, I would appreciate it! The GTX runs very strong, but I'd like to try to piece together the history on it if I can.

    Thanks!


  2. #2
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    so what's the good price for a 97 gtx?

    you'll often see skis with hundreds of hours on the meter..could be on a rebuilt engine. easy to spot(well kinda)..but with 160 in the jugs..that's a darn good deal.

    Heck @ 125psi is _still_ a darn good deal

    one of my favorite jetskis to ride here btw.

  3. #3
    flyin' the friendly skies airbornexp's Avatar
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    I had over 250 on my first 787 engine before it started showing signs of lower compression. Last compression check I did on that engine was mid 150ish. As said above as long as its above 100 I'd ride it till it blows then spend $800 and rebuild it.
    You can always tell a rebuild if the paint is missing on the head bolts or freshly painted

  4. #4
    Ryguy425425's Avatar
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    Thanks for all the comments! I think I might find a shop that will lend me a compression tester that would be a little more accurate then my $20 Wal-Mart unit, and see what it gives me. After I take it for a ride tonight I'll try to degrease the engine and take a look at the head bolts (It's dirtier then I like to admit). I am really curious now, since yours didn't show any lost compression until 250 hours.

    I guess the price probably wasn't outstanding by most standards, but I found this one for about $600 cheaper then they normally run here in Atlantic Canada. I haven't had it on a good long run yet, but it's looking like it is going to be an amazing ski!

    From what I've read I can likely get a few hundred hours more if I take care of it, I'm just catching up on maintenance right now.

  5. #5
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    you can often borrow a decent gauge at the local auto parts shop for nada. should have one available in your toolbox. handy to have

    use good oil and the enginewill last quite a while, I have a couple of older customers who have 300+ hours on thier 787's

  6. #6
    smoofers's Avatar
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    In my opinion, the biggest thing is if the compression on each cylinder is within 5-10% of each other. Lots of people like to trash Sea Doo 2 strokes with stories of problems etc. In reality, so many of them were produced and sold and bought and owned by people who have no idea what regular preventative maintenance is... I've seen plenty of Sea Doos that have HUNDREDS of hours on them and run just like new. Sea Doo has always been the leader of the pack as far as speed and horsepower are concerned and with that comes just slightly more maintenance than an old Yamaha or Kawi.

    I wouldn't worry too much about your compression numbers if they are close to equal. Just keep up with the regular maintenece items and make sure you change out any of the OEM fuel lines from that era along with keeping the carbs clean and oil lines in good shape! It will continue to run for years!

  7. #7
    Ryguy425425's Avatar
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    Sounds good! All of the fuel lines (except the vent lines) were replaced a few weeks before I bought the ski. The first thing I did when I brought it home was order a fuel and oil filter, as well as the two oil lines they recommend replacing (They didn't look bad, but I don't want to take the chance). I think I will have to clean the carbs this week, as the ski topped out at 6800 RPM (Would spike to 7k for a second, then cruise at about 6780). It died every time I tried to pin the throttle, but cruised along fine at 3/4 throttle. I may test the voltage regulator today, and if cleaning the carbs doesn't help I'll have to attempt to adjust them (I cleaned the fuel selector valve when I flushed the lines). If all else fails, I'll have to start a thread!

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