i just noticed a new problem with my 305 TPI on my Formula 1990, the oil pressure is good (45) for about 10 min while running, then it drops to 30, then it drops to 10, and at idle it goes sometime to 0 and the motor tend to stops, i checked the oil, full operating range.

I recently changed all the valve seals on the engine since it was burning 1/4gal of oil / day, and now its burning 1/8, but its going in garage for the piston rings soon.

Maybe someone could tell me whats the problem (commonly) for a oil pressur drop like this! because before the valve seals change the pressure was always at 30 (oil being hot or cold).

srry for my english, i'm french, so if you do not understand something just ask ill explain my best!

 

It may be sludge dislodged during the stem seal change that has clogged the oil filter, pump pickup screen or has jammed the oil pressure regulator partially open. I had the latter occur on an engine that I cleaned that had 5 cm of buildup from running years with a clogged PCV system.
Change the oil and filter. The pickup screen can be cleaned when the rings are replaced. I assume that the crank bearings will be replaced with the rings. Throw on a new oil pump and the pressure will be fine.

 

alright, thanks ill try that