Oil pressure problem??

[Newkirkracing]

I have a 90 300ZX, I just put an engine in it for my son, the car I took the engine out of had wiring problems so none of the gauges worked, it had a miss in the eng. it was a valve not seating so I took the head off and had it fixed. got the eng. in and has very little oil pressure 5lbs but will fluxuate to 10lbs the lifters are rattling so I took the sub frame down pulled the pan and plasti gauged the bearings and they are like new...this eng has been rebuilt not too long ago by looking at it..so I go and put in a new oil pump...still hardly any pressure..any suggestions??? When the guy redid the head could he have forgotten something or a plug of some sort?? I know the oil gauge is correct cause I put on a mechanical gauge...plus the lifter noise....ANY suggestions would be greatly appreciated.

[nissanfreak12]

Did you prime the oil pump after you put the new one in?

[Newkirkracing]

Yes the new pump was primed. Just wondering if something mite have been left out when the head got redone or when they rebuilt the engine. (Not sure how long ago it was rebuilt or even who did it..it was in a car I bought just for the engine and the kid I bought it from doesnt know jack from a hole in the ground.)

[nissanfreak12]

Nothing that I can think of at the top of my head. When you pulled the oil pan, was it dented at all? Sometimes the right angle of a dent will press against the pick up tube and starve it for oil. It also could be a problem if the on the pick up tube if the seal at the end is just not good anymore causing it to suck in more air than oil or you could just have a clog.

Another area that may be of some concern is the oil filter adaptor, they have a couple o-rings inside that tend to get old and brittle, this could be an area to check for. Im not 100% sure if this will cause low pressure, but when I replaced mine, they were completely dried up and very brittle.