low oil pressure problem

hey guys! i may need some input from the inliner guys. i have a 56 235 motor that i keeps wiping rod and main bearings out . the motor has been rebuilt twice but still the problem exsist. so i disconnected the oil filter housing cause it didnt seem to be flowing fast enough through it.so what happens is the pressure is good for a few miles till the motor reaches operating temp then drops to about 15 psi, when i disconnected the oil filter i did plug the outlet and return on the block. but i just cant seem to keep the pressure around 30psi. also i questioned the oil pump pick up location, but they all seem to be a bit shallow. any advice would bve great. thanx

 

does it have a bypass valve/spring?

 

How was the engine rebuilt?

Bored, crankshaft clearances checked, new cam bearings etc. or did you simply replace bearings?

Is the 15# reading at idle or at speed?

15-20# at idle is an ok pressure.
If it stays at 15# at 2000 rpm or so, then you have problems.

Is the oil filter full-flow or bypass style?

 

I don't think this is your problem, but it's worth a look.

http://www.jalopyjournal.com/forum/showthread.php?t=368892

 

My experience with these engines is if they have slightly sloppy bearing clearances and an older oil pump they run about 35 psi at road speed with 20/50 weight oil and fully warmed up.The pressure at idle is not important so long as it's got more than 5 psi.
If you putt around town the engine will last ok with 15-20.psi. If you drive hard it might not last as long.
Parts get swapped around over the years.Later 235's have a .062 restriction built into the head to limit oil flow to the rockers.Lack of this restriction can lower oil pressure at lower engine speeds.