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  1. #1

    How to check 951 for blown head gasket

    After new top lost compression. Was 150 ea cyc after about 5hrs of careful break in. Then lost power no seizing. Never did any full throttle runs just starting to go up to full throttle.Checked with bore scope no scratches or pitting still on rich side. Looked through rave slots rings and cyl looks like a good break in. Even looked from under the pistons at cylinders. Barely a scuff on pistons.Top of pistons just starting to show a light chocolate color. It didn't appear as any water was ingested.
    Last edited by 153stars; 05-23-2013 at 02:57 AM.


  2. #2
    AndinoWatercraft's Avatar
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    No power as in low compression ?? or lost on speed or acceleration? Did you check your reeds ? a broken reed could cause lost of power. Also if the rave selenoid is not activating will make the craft lost power.

  3. #3
    SURFnTURF's Avatar
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    Is the pisser (while under load and or on the trailer in the water) spitting and or fluctuating in flow and volume ? Keep it revving constant above 5 k and see if it changes This is a sure sign of head gasket leaking into the combustion chamber

  4. #4

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    Any chance its an O-ring head?

  5. #5
    I have low compression now like 80 & 120. Reeds good doesn't really want to run now. I have reeds & carbs off. It is standard double layler head gasket. It was a new SBT that I had to rebore after poor breakin.

  6. #6
    SURFnTURF's Avatar
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    You have scored a piston/ring i would think.
    Broken reeds dont effect compression that much as it happens all above the transfer ports
    Pull the valves out and shine a torch into the slots and see for any scoring
    You will have to pull the head off and have a look as this is the only way to tell.

  7. #7
    I will pull the head but with the borescope and through rave valves it looks perfect. I have the adapter for an air hose with the comp. gauge just not sure how to use it.

  8. #8

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    Sounds like you are describing a leak down tester? Those are normally used for four strokes. Or are you trying to pressure test the cases?

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