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Thread: first launch in a while, mystery klunk thud

  1. #1
    berk
    got the boat wet for the first time this year (since feb) and i have mystery noises already. motor is on its second season, mild 383, real reliable so far. i launched and warmed it up a bit, but i actually had a pop rivet chunk sticking up the gas pedal, so when i pumped the carb up it stuck at about 2200 rpm for a few minutes while i figured out the problem. then i got er on plane and it started knocking real loud. limped it back to the ramp, thuds heard at any rev abouve 1100. could the warm up have killed something? to loud and thud-like to be a lifter i think. any guesses?
    also oil looked good before launch.

  2. #2
    RCB19
    Sounds like a rod bearing to me. Bummer!! Good luck man.

  3. #3
    SmokinLowriderSS
    The high idle shouldn't have hurt anything by itself. My 454 ran a solid 2,000 to 2,500 for 20 minuites this spring breaking in the new cam. Only a shortage of oil or a rod bolt loosening up should cause a rod bearing failure. Yea, sounds like a spun rod bearing to me too.

  4. #4
    Cas
    you positive it's coming from the engine? did you check the drive line? How about something that got sucked up into the pump?
    Just trying to think of simple fixes before going to the bad stuff

  5. #5
    berk
    you positive it's coming from the engine? did you check the drive line? How about something that got sucked up into the pump?
    Just trying to think of simple fixes before going to the bad stuff
    yeah my first thought was driveline but it felt solid to the hand. sound not coming from pump, but it is difficult to hear due to the aluminum hull and solid mounts, kinda like a big soundboard! DANG i was afraid it might be rod.
    unfortunately it was upstream/upwind to get back so i had to limp for o long way. hope shes not toast!

  6. #6
    Wicked Performance Boats
    Sound transfers thru everything. From past experience, I would disconnect driveline and run motor to isolate problem. Then you know that it's in the engine 100%. Then I'd wouldn't screw around, I'd pull the engine and drop the pan. Budlight

  7. #7
    berk
    isolated the funky jug, saw evidence of loose junk itting spark plug so i ran it with the plug out for a sec and a chunk of ring flew out into the bilge. LAME! is this what i can expect from forged pistons that havent seen more than 5000 rpm? :frown:
    can you guys line me out on the next step to get this thing wet again?
    pull head, pull motor, pull pan, pull piston, then what?

  8. #8
    SmokinLowriderSS
    I'm with Wicked. Disconnect drive and see if the ENGINE makes the noise for certain. If you still have it, yep, haul it out, flip it over , and open her up. If no noise disconnected, open the drive up and you will find SOMETHING loose somewhere. Good luck.

  9. #9
    Wicked Performance Boats
    Put it on the motor stand , strip the top off, turn it over and remove said piston. Go over everything, have knowledgeable friends or expert diagnose problem. Figure out what to do to correct problem and reassemble motor. Budlight

  10. #10
    berk
    the pistons are claimed to be Probe and the rings are hastings. dont know which models though. :boxed:
    can you buy one piston?

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