big block chevy knocking when cold

Old 11-19-2009, 08:07 PM
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j0694
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Default 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
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Old 11-19-2009, 08:31 PM
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TheYellaBrick
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How many miles on this engine?
Sounds like a case of major case of piston slap....
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Old 11-19-2009, 09:54 PM
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cepx111
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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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Old 11-20-2009, 02:37 AM
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fla1976
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Sounds like piston slap to me also. Are the pistons forged?
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Old 11-20-2009, 06:45 AM
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TheYellaBrick
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Originally Posted by cepx111
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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Old 11-20-2009, 11:22 AM
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j0694
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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
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Old 11-20-2009, 01:25 PM
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fla1976
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Here is some info on piston slap:
http://www.pistonslap.com/whatisit.htm
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Old 11-20-2009, 07:15 PM
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mopar1968
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Probably Wrist pin knock :!: :!: But then again it is a Chebby :!: :lol: :lol: [Just kidding]



''JUST MY TWO CENT'S WORTH''
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Old 11-23-2009, 04:41 PM
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Scooterz
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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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Old 11-23-2009, 06:08 PM
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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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