zero oil pressure

My 1972 850 spider has an erratic 30psi oil pressure when cold. Once warm, it drops to zero!
We've replaced the oil pump and checked the pressure gauge is reading accurately.
My mechanic says the engine appears to have been rebuilt recently, good shells and pistons, but he has no experience of old fiat engines. Fiats usually rust away over here.....
He wonders if anyone has any information - tolerances, part suppliers etc ...about the oil seal mechanism at the filter end of the crankshaft.
Thank you
Paul

You say you've checked the oil pressure gauge, but have you checked the sending unit? They frequently go bad, on many makes/models, not just the 850.

How did you verify oil pressure? I had a '72 850 Spider and the gauge always read at zero when hot. The warning light never lit except before starting, so it was actually fine, just a bad sender.

oil pressure

get a manometer and check a closer reading. it's a manual hand held gauge and will give a true reading of oil pressure.
then you will know.. oil pressure, gage, or internal problem.
mikemo