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  1. #1

    piston damage-98 polaris slh 700

    Last year I turned over my jetski and hydrolocked it. Damage was significant on no. 1 piston. So I had the cylinders bored and installed oversized pistons. Ran great for the last year topping out at 58 mph. Two weeks ago two riders started to tip and dove off without flipping it completely over, it only tipped half way. From then on it barely starts only running at full throttle. Did a compression check and there's no compression on cylinder no.1. Removed head and damage was significant to piston top and ring ridges. Cylinder was not damaged. Ordered a new piston, cylinder is being honed, was wondering if any one had any info on why this would happen since it didn't tip over the 2nd time. Thanx

  2. #2
    here is a picture of piston does this look like hydrolock?this is the same cyl. that did simular damage last year!other cyl. still looked perfect.but right after it almost flipped it would barely start.took plugs out right after no apparent sign of water.Click image for larger version. 

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  3. #3
    casey67's Avatar
    Join Date
    Sep 2006
    Welcome to Green Hulk !
    My first impression , I think it was overheated.
    Do you get alot of water in the hull after riding ? That would make it easier to roll over or almost roll over

  4. #4
    no water in hull did ride for 20 minutes after i finnally started it,with could explain overheating,wondered if ring caught ex. port to cause initial damage?

  5. #5
    like i said i ordered new piston,took cyl. to machine shop to have honed,i checked entire cooling system all fine,no blockage,im still worried about this happening again,could it be caused from a lean condition?

  6. #6
    casey67's Avatar
    Join Date
    Sep 2006
    No,the ring getting stuck would leave dents in the piston, it would not cause melting.
    Looking closely at your pic's,it looks like you had good wash pattern before it blew-up. Which really makes me think it was hot.

  7. #7
    thank you 4 your advice,im going to check cooling system again for blockage,do you have any thoughts about what could have made it run hot?im going to check thermostat again,checked popoff valve,intake screen,ex.manifold screen and orface,crossovertube,i will check hoses tonight for blockage.

  8. #8
    also other cyl.was in perfect condition, perfect only bad cyl. got hot,thats what i dont understand?

  9. #9
    When you refer to cylinder #1 is that the PTO or the mag cylinder? I have had 2 failures of PTO pistons in similar way. Both occured when my kids were riding 2 up. The first time they almost tipped it and jumped off as you described. Both times the rings seem to have caught on the exhaust port. I'm at a loss for an explanation hope someone can help. My ski is a 96 SLX780

  10. #10


    mine was mag cyl. both times.did your piston look like it melted somewhat on top? i've got the new wsm piston,rings,pin,gaskets,had cyl.honed,3 hours and i would be ready for water but i am thinking i need to find out why this has happened twice,next time i might not be so lucky.

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