big block chevy knocking when cold

[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]

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

[fla1976]

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

[TheYellaBrick]

Sounds like a case of major case of piston slap....

Huh DD?
Case of beer maybe....lol

:oops: :oops: :oops: 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.

[russ67chevelle]

gotta remember those dodge guys are a lil different :?

a chebby slam.... :roll:

[DRTRCR22]

When was the last time you adjusted your lifter rocker arms? If they are hydraulic lifters, as the cam wears the lash gets greater until they will start ticking away when cold. If the noise is up high it could be rocker arm lash slap. It is the easiest and simplest thing to check first. Just a 1/4 turn in of each rocker nut will tighen up your hydraulic lash to within specs. If solid lifters you should be checking them at regular intervals anyway...

[mopar1968]

Yes we sure are, we own the best :!: :!: :lol: :lol:



''JUST MY TWO CENT'S WORTH''
from the quiet one

[russ67chevelle]

:roll:

[Pwmax]

I would also say piston slap, If you have bearing problems, at idle, you would have 0 oil pressure, that would go up a little as you revved it, and the knocking would be proggressivley getting louder and louder the longer you kept driving it like that, and, it wouldn;t go away when it warmed up. Years ago, I has a 350 that would do that. Stock, who knows how many miles, I bought it as a runner, put a cam in it, intake, carb etc, and BEAT the snot out of it. For 3 years it did the same thing. Every morning, knock for about 2 minutes, and go away.


Frank

[j0694]

thanks for the replies