I've just rebuilt the engine in my '79 Spider. After cranking it for a good 30-45 seconds, I get no oil pressure on the guage. Thinking the gauge sender was bad, I substituted another. Same thing. There's no oil drips on the back of the sender either, leading me to believe that the pressure is not building up. The oil pump is a new one, and yes, there's oil in the pan. I've never had a car take longer than this to build up pressure, so I think something's wrong. I know the oil pump is turning - the distributor is turning and its run by the pump. What am I missing here? Thanks!