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454 mystery knock

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by agrezy1, Jan 5, 2003.

  1. agrezy1

    agrezy1 Registered Member

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    got a mystery knock in 454 its not in my burb but in my motorhome the knock does not sound like a rod its like a light knock all the time can here it mostly from top of engine and pass. side outside sounds like a rotating knock heres what i have done so far,,ran motor with all belts off,new water pump pulled fuel pump out along with rod pulled intake and inspected lifter valley,checked end play on crank changed flexplate and trans all this made no differance the knock is not loud enough to here over 1500 rpm the guy i bought it from says the whole time he owned it never got worse and he put 25,000 miles on it am i just being paranoid? its a 1985 carb.model with factory oil cooler any help woud be great.
     
  2. unsane

    unsane Guest

    Timing? Anyone else?
     
  3. Sandman

    Sandman 3/4 ton status Author

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    Could be cam bearings maybe.
     
  4. thatK30guy

    thatK30guy 1 ton status Premium Member

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    How about a lifter? /forums/images/graemlins/confused.gif
     
  5. Sandman

    Sandman 3/4 ton status Author

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    Yeah, a stickey might do that.
     
  6. 4x4Freak

    4x4Freak 1/2 ton status

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    Are all your plug wires in good shape? When my parents got their motorhome it had a tapping sound, kinda like a loose rocker arm. Turns out there were a couple wires loose that were jumping fire.
     
  7. 4x4k20

    4x4k20 1/2 ton status

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    try cleaning the top of the pistons with some injector cleaner it could have some carbon built up on them . i had a 86 454 that had a knock and thats what it was .
     
  8. motorheadnelson

    motorheadnelson Registered Member

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    Possible wrist pin/ cracked skirt, but they usually are loudest when cold. Maybe even something as simple as an exhaust leak.
     
  9. Ditchdigger

    Ditchdigger Registered Member

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    Try lookin at your Exhaust Manifold gasket,
    I have been fooled before where I thought it was
    a lifter and turns out to be an exhaust leak
     
  10. Klink K5

    Klink K5 1/2 ton status

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    Motor Homes are nortorious for exhaust manifold leaks. I would look there first. They generate so much heat, I've seen the manifolds warp so bad that the shear the bolts off the head and warp like a banana! Hope this helps!
     

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