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  1. #1

    787 oil in cylinder/ Convert to premix?

    1999 GTX 787 RFI. The front cylinder will fill with oil when turning over the engine. I am wondering if it is a crank seal or if there is a oil check valve that could be stuck. It has ran fine until it sat for about 10 days.

    Would there be any way to premix the RFI?

    Any help would be appreciated


  2. #2
    KrunchovXPL-GTX-RX's Avatar
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    Sounds like a bad crank seal on the Rotary Valve Shaft cavity. This is a typical failure for RValve engines.

    The fuel is injected into the transfer port so I do not think you even can pre-mix an RFI. It would not fix the problem anyway, since you still have to have oil for the RV Shaft if you pre-mix an RVavle engine and the seal would still leak and it would still flood that cylinder with oil if given enough time.

  3. #3
    96XPSS's Avatar
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    It is more likely the 518 sealing the case halves failed over the crank seal. You can remove the engine and flip it upside down, remove the bottom case, clean all mating surfaces with carb cleaner, reseal with Three Bond 1211, and I bet she never fills with oil again.

  4. #4
    Thanks for the Help! Would a failed RV shaft seal only flood one cylinder, or is it more likely the case seal?

  5. #5
    KrunchovXPL-GTX-RX's Avatar
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    Never thought of that since I have not run into it. The fix is not expensive so if that was not it you are not out a bunch of cash with the same problem.

    The irony is if you have the crank rebuilt or buy a rebuild and then put it back together it would fix it regardless.

    Still, I try not to spend money if I do not have to so 96XPSS's suggetion makes sense.

    There are two seals so if one seal failed, it would only be one cylinder.

  6. #6
    Thank, I've downloaded a service manual and will do a pressure test to isolate the problem. Where would be a good place to find a hand pump locally?

  7. #7
    96XPSS's Avatar
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    Normally the rear cylinder fills when the RV shaft seal fails.

    When you pressure test the cases, the leak between the cases and the crank seal will not be distinguishable, as they are right beside eachother.

    Good luck!

  8. #8
    OK, I've decided to replace the seals and reseal the cases, that should take care of the problem. I've pulled the engine (2nd time this summer), is there anything i should know before splitting the cases?

  9. #9
    TX21's Avatar
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    Quote Originally Posted by tt996gt3 View Post
    OK, I've decided to replace the seals and reseal the cases, that should take care of the problem. I've pulled the engine (2nd time this summer), is there anything i should know before splitting the cases?
    Dont break that stupid magnito cooler cover on the front of the motor. I broke the first two that I did engine rebuilds on. Its got two plastic nipples for water cooler lines and is really easy to catch on the hull when pulling the motor out.

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