Classic/Antique Car Repair: Oil Pump Question, oil pressure gauge, cam bearings

Question
I have a 72 Chevy C-10 LWB, and I just recently started to put it back together. One of the major problems I am having is that my oil pump is not pumping. When i was rebuilding my engine out of the truck I never touched it.
I made sure that all my push rods cleaned out and pumped some oil in it with my oil gun and watched it flow out the other end. I primed it using 3/8 drill turned the motor about 3 minutes. I thought maybe I am not turning it fast enough. I then used a 1/2 turned it for 3 minutes and only got a few drips on the driver side valves toward the back of the motor. Both times priming the engine I was getting a reading of 3/4 on my oil pressure gauge

Any suggestions in this matter would be appreciated

Thanks,
Paul

Answer
Paul, here is what I would due in this case. From what you say I assume that this is a V-8. On that engine the oil from the oil pump fills the oil filter and then to the main oil galley in the block. That galley feeds the cam bearings that feed the main bearings. At the back of the block inside there is a split in the galley sending oil to the lifters which then sends oil up the push rods. The oil pressure sending switch is located at the back of the block. I would remove it and make a run to the hardware store for some fittings and a piece of copper tubing. I would make this line up so that I can direct the oil flow into a jar or can while I am turning the drill. If you have good flow the problem is not the pump but perhaps the lifters not pumping up, or the lifters not properly adjusted so that the oil is leaking out between the lifter and the push rod. I have found engines with holes worn in the bottom of the lifters allowing the oil to leak back into the pan rather than be pushed up the hollow push roads. But again make an assumption, that the lifters were replaced. Check the oil flow and then go from there.
Good Luck.
Brad