3.0 omc knock and low oil pressure

[gwershing]

No it's not as simple as that. I have a 1989 3.0L OMC. I rebuilt the engine with all new parts. I had trouble getting it running, but finally got it to idle. However it's noisy. It knocks, and I'm thinking it is the lifters. (it is a knock and not the clack you hear when the rockers need to be adjusted) It quiets down quite a bit at higher RPMs. ...but also: the oil pressure fluctuates at a high frequency at low speeds. yet stays above 40 PSI. However when I speed up, the noise quiets and the oil pressure drops to nothing.
Could a lifter problem cause the oil pressure to drop at high RPM?
Do these two problems have anything in common?
It seems counter intuitive that the engine would quiet down when the oil pressure drops.
Help, please.

 

[Bt Doctur]

Re: 3.0 omc knock and low oil pressure

Did you check all the clearances and "pre-oil" the motor prior to the first start, have the lifters been adjusted static or hot.

 

[gwershing]

Re: 3.0 omc knock and low oil pressure

Plasti-gauged all the bearings - good.
Used assembly lube during installation.
Primed oil pump with drill through the distributor hole after engine was assembled.

 

[gwershing]

Re: 3.0 omc knock and low oil pressure

Lifters adjusted with engine at operating temperature, while running. Loosened until clacking, tightened until quiet + 1/4 turn.