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  1. #1

    Join Date
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    Results of my compression Test

    As my investigation into my 780 SLX continues, I performed a compression test tonight. The front cylinder was 90 psi after several cycles of the starter. First time I hit the starter it went to 60 and then when I hit it again it went to 90 psi.

    The center cylinder was at 85 psi and the rear cylinder was at 100 psi.

    I did the test with the entire exhaust system including the exhaust manifold removed, and with the carbs removed. Would this have an effect on the numbers? I also had the other 2 plugs removed....would that effect the numbers? Please excuse my ignorance, but I have never done a compression test before.

    Other than that I guess this would suggest this is just a tired, worn out motor?

    What do ya'll think?


  2. #2

    Join Date
    Sep 2006
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    topeka,ks
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    3,332
    major engine trouble , scored or hole in the cly ,

    user malfunction , did you hold the throttle wide open ?

    its kinda good you have some compresion might be an easy fix like an oring or small bore clean up job

  3. #3

    Join Date
    Aug 2007
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    Cypress, TX
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    Can I pull the heads without damaging the gaskets? I want to take a look at the cylinders.

    I never even had it on the water. I bought it for a grand thinking it just had a fuel problem. It ran for a week, not well, but it ran and then started making a horrible noise.

    If the opinion is the same of everyone then I am just going to cut my losses and sell it.

  4. #4

    Join Date
    Sep 2006
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    topeka,ks
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    3,332
    well bud ill tell ya unless you spent close to 2500-3000 for your ski you dont get a easy fixer or perfect one ,

    these guys right here will make you love your polaris plus engine parts are cheap and wrenching is hard as changeing brakes

    http://new.photos.yahoo.com/radracin...60762356278416 this is the man
    Last edited by Bone1050; 08-28-2007 at 10:51 PM.

  5. #5
    sea~smith sea~smith's Avatar
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    Aug 2007
    Location
    Ottawa Canada!
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    Hey,

    I bought my sl900 3 weeks ago, just found out my cylinders were so bad the mech had never seen anything like it. So here I am with the carbs being cleaned and in pieces, gaskets on order and rebuild kits, a search for 3 new cylinders and 2 piston kits... and I just found out the middle piston broke appart and pieces fell into the crank case so I need to take the engine out and the crankcase appart. Soooo its been a crazy 3 weeks, and the funniest part is that it was running like a bat out of hell on week one, which was enough to fuel my spending to repair it.

    The way I see it, it isnt about the money at this point, If I wanted I could have bought something more expensive, but now I know everything that has gone on in my first jet ski and I am having a blast working on it. This forum is unreal and I would be lost without it. People sell parts for fair prices because they know what it feels like to have a jet ski on dry dock.

    depends what you want, something to rip around on, or something to rip around on that you know you fixed by yourself.

  6. #6

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    Aug 2007
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    Cypress, TX
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    I've definately got some thinking to do. I guess I'll sleep on it and figure it out tomorrow.

  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Cleveland OH
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    Compression does seem kinda low. Whether the exh manifold not installed has anything to do with it I don't know. You can remove the heads, just use copper gasket spray when you reinstall the gaskets. (it's not recommended to reuse them, but I and others have done it with no issues)

  8. #8

    Join Date
    Aug 2007
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    I pulled the heads last night and the 1st and 3rd cylinders / pistons looked good, but were a little loose in the cylinder so they probably just need new rings.

    The center cylinder had a quarter sized dent in it and a small gouge in the side of piston, enough for me to see the top of the ring. The center cylinder had a few marks in the wall, but still felt smooth to the touch. I know that doesn't mean much though.

    Could just get a center cylinder sleave pressed into the jug?

  9. #9
    AWA Member 32DegH2O's Avatar
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    If the gouge is small enough, you might be able to just get by with a good hone job...at worst just have it bored out to the next size. No need to replace the sleeve at this point. The dent you are referring to in the cylinder is actually the piston starting to melt...running to lean most likely. But you are probably in luck as it sounds like you caught the problem early. I would take all three cylinders and have them honed, put new rings on them and of course replace the one piston...maybe all three just to give it a fresh top end. Now you just need to make sure nothing happend to the crank with metal debris getting in there. If it seems clean than you got lucky. Now you have one more thing to do, find out what caused the lean condition in the center cylinder...would look at the carbs, open them up and see if you notice anything that shouldn't be.

    As for compression testing, having the manifolds off really isn't going to affect things much, not enough to vary what you are getting from each cylinder.

  10. #10

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    As someone earlier said it was probably due to operator error. I had it hooked up to the hose in the driveway and ran it a few times while trying to fix the fuel delivery problem when it started sounding terrible.

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