I have a BBC Merlin 3 block, when I prime it with a drill, I am getting ungodly oil pressure, wrapping the needle on a 100 lb gauge and slamming it back on the 0 peg. I took the oil pump off and double checked the bypass valve and it works free. Any ideas what could be causing this excessive oil pressure?

Some are adjustable I believe, And also do you have a bypass valve right where the oil filter would screw on to the engine block???

What are your oil clearances and what is the weight of the oil. Drill rpms? If your oil pressure is that high on the drill you will really have some problems with the engine running. I just got done rebuilding two engines that had HIGH OIL PRESSURE, lIKE OVER A 100 @ IDLE, THIS WAS FROM SOMEONE ELSE. It wore the distributor gears out and the gear on the cam, also the force put on the gears in the oil pump.

Absolutely I agree it will wear stuff prematurely, I am pulling the motor in the AM, just looking for ideas on the cause. I am down to the pump bypass sticking or there is a blockage after the oil comes out of the motor, that woild go to remote filter and cooler and then goes back in to the block. I bypassed the filter and cooler with AN unions, because it was blowing the filter of the remote mount, I wanted to eliminate that piece. The oil is 20w50, the main clearance is .0025, the rod clearance is .003. It is definitely way out of line.

Apparently the problem was the oil pump, removed it and replaced it with another pump, and walla, 80 lbs on the drill. I can't believe that the pump was the problem, it was the Melling 10777, I would have to surmise that even though the bypass worked free that it wasn't opening properly. Thanks for the input.

Did someone else build that engine. The problem I addressed, was the same 10777pump had a .170" cam degreeing bushing behind the spring along with the old syle washer installed behind the pin. I called the original builder to ask him about this, he said; he does all his pumps the way. He has a BIG NAME, I guess this is how you give a 1yr warrenty and get repeat buisness. I couldn't believe what I just heard! Was wondering what, I've been doing wrong in business.
Did your pump only have the pin & spring in it only? I always test my pumps in a tank with a pressure gauge before installation, saves alot of oil pressure differences between engines after assembly. I would also expect to see mains around .0032 and rods around .0025
Glad you found out the problem, before you had alot of problems. Mark