j0694

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

TheYellaBrick

How many miles on this engine?
Sounds like a case of major case of piston slap....

cepx111

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

fla1976

Sounds like piston slap to me also. Are the pistons forged?

TheYellaBrick

ops: ops: ops: a FULL case of re-re-repeat , It's the pain meds, I swear it ! :roll: :shock: :shock:

j0694

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

fla1976

Here is some info on piston slap:
http://www.pistonslap.com/whatisit.htm

mopar1968

Probably Wrist pin knock :!: :!: But then again it is a Chebby :!: :lol: :lol: [Just kidding]



''JUST MY TWO CENT'S WORTH''

Scooterz

I have heard solid lifters do this when cold... then go away when warm... do you have solid lifters??

kwkracing

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.