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  1. #1

    787 water leak at cylinder gasket? What size gasket?

    Just when I thought it was all done, a problem. Took my 96 Challenget out today for a quick run. Weather sucked but we still had fun and ended up staying out a couple hours. Had to try out our impeller that Impros repaired. It looked nice and new! Ran great and on the way back I decided to look in the engine compartment to make sure all was well in there. To my surprise I had about 3 or 4 gallons of water. It has always stayed quite dry so I knew something was wrong. Then I saw a stream of water spraying out just above the plastic PTO flywheel cover. (In photo you can see water shooting out near green gasket material.)

    What I was curious about is if should I go ahead and tear down the motor and order a new cylinder gasket or is it more than likey something that tightening the bolts in the cylinder block will correct?

    I also noticed that there is a 0.3, 0.4, 0.5, 0.6 and 0.8mm gasket listed in the parts catalog for my motor. How do you decide what thickness to use???

    Anything else I should do as far as maintenance, or things I should check while I have it apart?
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    Last edited by PilotSmith; 02-24-2008 at 01:07 AM.


  2. #2
    Dr Len's Son MaxMike's Avatar
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    When was the last time you took off your R.A.V.E. Valves and cleaned them?? If you haven't done that in a while, do it now since they get pretty gunked up. Believe me, I know from personal experience.

  3. #3
    Quote Originally Posted by MaxMike View Post
    When was the last time you took off your R.A.V.E. Valves and cleaned them?? If you haven't done that in a while, do it now since they get pretty gunked up. Believe me, I know from personal experience.
    Couple days ago... They were dirty and one diaphgram was not seated.

  4. #4
    Dr Len's Son MaxMike's Avatar
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    you just gotta make sure to clean them every once in a while. my boat was used, and the previous owner must not have known anything so my dad and i took them out and 3 out of 4 of them (twin 787 engines) were melted from being stuck in the down position. man was that a nightmare!

  5. #5
    Yikes! Glad the one in mine that was not working was not melted. It ran great today.

    I just saw in the shop manual the answer to my gasket question. You need to pick the gasket thickness that gives you the correct squish gap of 1.2-1.6mm. I measured mine and got measurements of 1.7mm so it looks like I should get a thinner one to reduce the gap size.

    Sounds like by reducing the squish gap you are also boosting compression a little? Manual says too much gap and you lose power and too small you get detonation. So I guess the goal is to get it close to 1.2mm?

  6. #6
    If shes got boobs or a throttle, I'm on it! badvinny's Avatar
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    Any less than the 1.2mm(.050") will cause detonation, even more chance if you run regular fuel instead of premium. I also think that retorqueing the bolts will not repair the problem.

  7. #7
    The bolts are tight. Looks like the gasket simply failed. In process now of pulling stuff apart to get to it. I have 2 Super BN rebuild kits. I guess while I have it all off I will rebuilt the carbs too. Runs fine but I guess after 12 years probably won't hurt to put new guts in them while they are off.

    I don't know the thickness yet of the gasket in there now. But given my squish gap is a little over the max recommended, I will put a thinniner one in. My gap is at 1.7 so I will put one in 0.3 thinner to shoot for 1.4 which is in the center of 1.2 to 1.6 range. That way if I am off a little on the measurement I should still be within specs.

  8. #8
    The ski's have taken a "backseat" to the Corvette DarthAWM's Avatar
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    Quote Originally Posted by PilotSmith View Post
    The bolts are tight. Looks like the gasket simply failed. In process now of pulling stuff apart to get to it. I have 2 Super BN rebuild kits. I guess while I have it all off I will rebuilt the carbs too. Runs fine but I guess after 12 years probably won't hurt to put new guts in them while they are off.

    I don't know the thickness yet of the gasket in there now. But given my squish gap is a little over the max recommended, I will put a thinniner one in. My gap is at 1.7 so I will put one in 0.3 thinner to shoot for 1.4 which is in the center of 1.2 to 1.6 range. That way if I am off a little on the measurement I should still be within specs.
    While you are rebuilding your carbs check the fuel lines and see if they are grey and stamped with the word "Tempo" on them, if so replace them.

  9. #9
    Fuel lines look like standard black fuel lines. They are likely the stock lines as they have the crimp on factory hose clamps.

    Just printed out the Mikuni shop manual so off to rebuild them I go. Keep the suggestions coming!

    Thanks

  10. #10
    The ski's have taken a "backseat" to the Corvette DarthAWM's Avatar
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    Quote Originally Posted by PilotSmith View Post
    Fuel lines look like standard black fuel lines. They are likely the stock lines as they have the crimp on factory hose clamps.

    Just printed out the Mikuni shop manual so off to rebuild them I go. Keep the suggestions coming!

    Thanks

    If they are black I would say you are ok, the skis around your year model had trouble with the fuel lines, namely that the material of the fuel line dissolved in fuel

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