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Thread: big block chevy knocking when cold

  1. #1
    Junior Member SHOW GUEST
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    big block chevy knocking when cold

    i have a big block chevy that has a pretty noticable knock when it is cold started then goes away once heat is built up. any suggestions on what is causing this

  2. #2
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    How many miles on this engine?
    Sounds like a case of major case of piston slap....
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  3. #3
    Senior Member RACING JUNKIE
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    Quote Originally Posted by DrivingMissDD

    Sounds like a case of major case of piston slap....
    Huh DD?
    Case of beer maybe....lol


    Is the knocking noise down low or towards the top?
    What is the oil pressure? > hot?

    Usually a rod or bearing noise will get worse when hot.
    They way you described it, it kinda sounds like a lifter taking it's sweet time priming up.
    A piston slap will sound similar, after a few minutes of driving they'll heat up and expand which quietens them down, either problem is no biggie, drive it till the wheels fall off I say.

    What type of oil filter you using?

    El~ cheapo filters like a "FRAM" the anti drain back valve never works, try a wix, napa brand or purolater.

    The 'good' filters will hold some residual pressure and stay full after you shut the motor off - when you start it up (cold) the motor wont do all that klinking and clattering till the oil pressure builds up.


    Something to think about.


    Goodluck, Cp
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  4. #4
    Senior Member RACING JUNKIE fla1976's Avatar
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    Sounds like piston slap to me also. Are the pistons forged?

  5. #5
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    Quote Originally Posted by cepx111
    Quote Originally Posted by DrivingMissDD

    Sounds like a case of major case of piston slap....
    Huh DD?
    Case of beer maybe....lol
    ops: ops: ops: a FULL case of re-re-repeat , It's the pain meds, I swear it ! :roll: :shock: :shock:
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  6. #6
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    thanks for the input guys
    it has forged pistons and oil pressure when hot is around 40 psi idling at around 1200 rpm
    it doesnt sound like a rod knocking to me though

  7. #7
    Senior Member RACING JUNKIE fla1976's Avatar
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    Here is some info on piston slap:
    http://www.pistonslap.com/whatisit.htm

  8. #8
    Senior Member RACING JUNKIE mopar1968's Avatar
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    Probably Wrist pin knock :!: :!: But then again it is a Chebby :!: :lol: :lol: [Just kidding]



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  9. #9
    Senior Member RACING JUNKIE
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    I have heard solid lifters do this when cold... then go away when warm... do you have solid lifters??
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  10. #10
    Senior Member RACING JUNKIE
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    I have a street driven engine thats a little loose on the crank, When its cold outside it knocks about 3-4 times when it first starts up.... i use to worry about it, but after it got 75,000 miles i quit.


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