My ol' '87 had a no-oil-pressure problem at start-up for years. Sometimes I'd really have to rev it to get pressure. I figured 'so what,' and it kept running for years. A couple of owners later I heard it threw a piston through the block, but I can't establish a definitive correlation...

FastEddy has suggested using a shim in the oil pressure relief valve in past postings, as I recall. but that involves getting that front cover off. Don't know if that would help anyway.

If you're using a Fram oil filter, get rid of it (IMHO) as I regard the anti-drainback valve as being suspect.

John B.