A knocking sound

[4x4Cowgirl]

Well, I just got my truck, and this engine is supposed to be a fresh 350 with corvette heads.... I changed out the oil and spark plugs and did a tune up on it, and I still hear a knocking noise. I can't quite tell if its the actual motor that is knocking, (maybe a lifter) or if it's somethin else... It seems to be more significant when I'm on the gas... When I let off, it quitens down.. Has anyone had this problem before? Any help would be GREATLY appreciated!

[zieg85]

A slightly loose lifter can sound like a knock.

[maddog]

Does it make the knocking sound when it is cold as well when motor is at opperating temp.

[4x4Cowgirl]

at operating temp.  Ive heard it could be the bearings?

[VileZambonie]

Kinda hard to tell without hearing it but a mechanic's stethoscope will help you pinpoint the noise.

[maddog]

Sounds like a rod bearing to me, on cold start it will be faint as oil heats up and thins out noise should get more intense, hold foot on break in gear and Little gas at same time, if noise increases it most likely a rod bearing if noise doesn't change could be a lose rocker (rocker/rod bearing are a difference sound )

[4x4Cowgirl]

Alright thanks a lot guys 

[oldwhity]

I know it might be a shot in the dark but i'd also check for exhaust leaks.

[Irish_Alley]

i had my head gasket, header bolts back out a little and i thought i blew the motor. also you happen to know your comp. ratio?