I am exhausted reading oil pressure threads, and found no Joy.
I just rebuilt my 1966 A65L engine. Main bush clearance rod bearings, end play all good and properly fitted. Before fitting the oil pump, I took an old style oil can put the tip in the hole and pumped oil through the engine. Saw the oil weeping around the rods, and even out the oil in the left connecting rod. Very pleased. I oiled up the pump, turned it by hand to lube the pump internally. Finished the rebuild and installed the engine. I filled the external oil filter with oil. Yes its on the return side. I dumped .5qt of oil down through the head liberally coating the rockers, and adding "splash" oil to the sump for startup. Kicking through many times with out spark plugs, I had oil returning to the tank. I was "pumped"

Spark plugs back in, started the engine, oil flowing back to the tank, for a little while only!!! Probably just the remaining oil already in the sump. Still running, to my horror, no new oil coming back, oil tank is cold, 1000 rpm, idle, what ever speed no oil coming back. I turned off the engine deeply depressed thinking about what damage have I done to all my new tight bearing parts, and why am i not circulating oil.

If it was a stuck oil pressure relieve valve, I would still show flow, as the oil would go right to the sump. Same goes with improper clearances, if that was the case, I would still have oil filling up the sump. I know the return side of the pump works even at kick over speed.The tach works so I know the pump is spinning.

Is it even possible to install the ball and spring under the oil pump "wrong" somehow, without doing physical damage? With out having the engine apart, and following the oil holes, I cant understand what the ball is doing, or where it is, in relation to the "oil in", "oil out" of the pump ports. If the ball is stuck, would that prevent oil from getting to the pump? Perhaps someone could draw a pump and ball schematic? My Bsa manual doesnt show that kind of detail. What testing can I do with out disassembly of the primary side? Should I be able blow air through the oil feed line through the oil hose block junction, or apply vacuum. It seems like I am not getting oil to the pump. The hoses are connected to the tank properly.

thank you

keep your "oddies" lubricated, and carry a dime