Problem with my jet boat... Need help in diagnosis please...
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Problem with my jet boat... Need help in diagnosis please...

  1. #1
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    Default Problem with my jet boat... Need help in diagnosis please...

    I was runnin' at about 4200 RPM and all of a sudden the RPMs dropped to 3800 (and stayed there for awhile) and engine sounded like there was somethin' knockin' like when valves need to be adjusted [type of sound]. I shut the motor off immediately and drifted back the 4 miles to the ramp and only started it a couple of times trying to get away from the rocks and to the middle of the River and to finally get back to the ramp. But never rev'ed it above 2000 RPM. I should say though that I could barely get it to idle when attempting to restart as it kept stalling...

    I also noticed that there was a lot of smoke coming out of the exhaust on the port side of the boat so figured that somethin' gave out on one of the cylinders on that side of the engine. Did a compression check and what do you know... all cylinders checked except one on the starboard side! which reads 0... nada... I mean no compression at all. To give you guys more clue, the spark plug on that cylinder is missing half of the tip on the center electrode.

    So, here are the questions that I'd appreciate you guys' thoughts on:


    1. If the "no compression" cylinder is on the starboard-side, why is the smoke only coming out of the port-side exhaust manifold?
    2. I took the valve cover off and everything looked good as far as springs, push rods, rocker arm, etc. What do you suppose gave out inside that cylinder?
    3. Do you think that the fact that the spark plug is missin' half the tip of the center electrode, means that I'm dealin' with a nasty case of detonation, which could have caused a big hole in the center of the piston (and thus the reason for not having any compression)?
    4. Or could it just be the compression ring that somehow blew?
    5. One last question... I'm hoping that it is just a head gasket... But, shouldn't I be getting at least some compression if it was the head gasket or is it possible that blown head gasket could cause zero compression?

    Thanx all in advance for your thoughts... I just don't want to start tearin' into it blindly and end up doin' bunch of unnecessary work.

    Mike...
    Last edited by Mike123; 06-13-2010 at 10:34 PM.

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  3. #2
    Senior Member ClassicBoats's Avatar
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    To me It sounds like a piston has a hole in it, Ist the electrode smashed?

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    Quote Originally Posted by ClassicBoats View Post
    To me It sounds like a piston has a hole in it, Ist the electrode smashed?
    Not smashed, just missin' half of its tip.

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  6. #4
    Senior Member jetboatperformance's Avatar
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    Sounds like you likely detonated a piston Bud , prolly time to pull the head to inspect Good Luck

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    Default Zero

    Which cylinder has zero. It might make an explanation for the smoke easier...Ray
    LOUD BOATS SAVE LIVES

  8. #6
    AKA OhOneWS6 Last Mohican's Avatar
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    Chris94l had the same symptoms not long ago. Turnout out to be a blown head gasket. While a hole in a piston from detonation is more likely you may get lucky. Only real way to know is scope the cylinder or pull the heads.

    http://www.texashotboats.com/forums/...?topic=10452.0

  9. #7
    Senior Member lbhsbz's Avatar
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    Quote Originally Posted by Mike123 View Post
    I was runnin' at about 4200 RPM and all of a sudden the RPMs dropped to 3800 (and stayed there for awhile) and engine sounded like there was somethin' knockin' like when valves need to be adjusted [type of sound]. I shut the motor off immediately and drifted back the 4 miles to the ramp and only started it a couple of times trying to get away from the rocks and to the middle of the River and to finally get back to the ramp. But never rev'ed it above 2000 RPM. I should say though that I could barely get it to idle when attempting to restart as it kept stalling...

    I also noticed that there was a lot of smoke coming out of the exhaust on the port side of the boat so figured that somethin' gave out on one of the cylinders on that side of the engine. Did a compression check and what do you know... all cylinders checked except one on the starboard side! which reads 0... nada... I mean no compression at all. To give you guys more clue, the spark plug on that cylinder is missing half of the tip on the center electrode.

    So, here are the questions that I'd appreciate you guys' thoughts on:


    1. If the "no compression" cylinder is on the starboard-side, why is the smoke only coming out of the port-side exhaust manifold?
    2. I took the valve cover off and everything looked good as far as springs, push rods, rocker arm, etc. What do you suppose gave out inside that cylinder?
    3. Do you think that the fact that the spark plug is missin' half the tip of the center electrode, means that I'm dealin' with a nasty case of detonation, which could have caused a big hole in the center of the piston (and thus the reason for not having any compression)?
    4. Or could it just be the compression ring that somehow blew?
    5. One last question... I'm hoping that it is just a head gasket... But, shouldn't I be getting at least some compression if it was the head gasket or is it possible that blown head gasket could cause zero compression?
    Thanx all in advance for your thoughts... I just don't want to start tearin' into it blindly and end up doin' bunch of unnecessary work.

    Mike...

    You either burned/broke a valve, have a hole in the piston, or blew a headgasket....I would lean toward #2 because the other 2 will generally still make SOME compression.

    Where are you located? I've got a boroscope you can borrow if you're local.

    As for the smoke from the other side...dunno. Weird stuff happens when motors blow up.

  10. #8
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    Default Exhaust crossover?

    Quote Originally Posted by lbhsbz View Post
    You either burned/broke a valve, have a hole in the piston, or blew a headgasket....I would lean toward #2 because the other 2 will generally still make SOME compression.

    Where are you located? I've got a boroscope you can borrow if you're local.

    As for the smoke from the other side...dunno. Weird stuff happens when motors blow up.
    That's why I wanted to know which cylinder has zero. The exhaust crossover COULD explain the errant smoke......As could a broken intake valve/piston pumping oil into the intake plenum as a cylinder on the other side is on the "intake" stroke...........Ray
    LOUD BOATS SAVE LIVES

  11. #9
    its just another day DK_Hallet's Avatar
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    Sounds like you busted a ring to me. Best thing to do is pull the head and check for all of the symptoms .Any which way its better to just pull the motor and pull it apart at this point. Sorry to hear this
    Something Wicked This Way Comes

  12. #10
    "BOUGHT NOT BUILT" 2FORCEFULL's Avatar
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    pull the head.....you can pull the head on just that side to see how far you have to go..
    Last edited by 2FORCEFULL; 06-14-2010 at 08:48 PM.

  13. #11
    Senior Member EVILFORCE's Avatar
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    Hole in the piston.
    No Fool Like A Old Fool is there?

  14. #12
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    Default Ring??

    Quote Originally Posted by DK_Hallet View Post
    Sounds like you busted a ring to me. Best thing to do is pull the head and check for all of the symptoms .Any which way its better to just pull the motor and pull it apart at this point. Sorry to hear this
    I've never seen a broken ring show ZERO compression....Even a small hole in a piston may show something for compression.......I'm leaning towards a snapped off valve, and a damaged piston......Ray
    LOUD BOATS SAVE LIVES

  15. #13
    What the Hell is That? 72Hondo's Avatar
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    I just had this happen. I burned a Spark plug down. I though all was well but it wasn't Zero compression on #2, pulled the head, piston looked fine, valve not burned/chipped/cracked etc. Was a little stumped until we sprayed a little LPS oil into the runners, niagara falls. We checked the others too all of them leaked except one. Decided to pull the other head and have the heads re done.
    Quote Originally Posted by Kyle View Post
    Log off and go float, hang in the party coves, Show and shine on the trailer, fill up the boat, wax it, v-drive, jet, outdrive, and if you got a canoe and your reading this, you sir, need to phucking upgrade.

  16. #14
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    Quote Originally Posted by lbhsbz View Post
    You either burned/broke a valve, have a hole in the piston, or blew a headgasket....I would lean toward #2 because the other 2 will generally still make SOME compression.

    Where are you located? I've got a boroscope you can borrow if you're local.

    As for the smoke from the other side...dunno. Weird stuff happens when motors blow up.

    Really appreciate the offer... I'm in south OC so if there is any chance that we can hook up so that I can borrow your Boroscope, that'll be great..

    Mike...

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