Hi
I have been restoring my 1967 coupe for a number of years and part of that was swapping the SBC that came in the car to a Pontiac 400. I bought an engine from a guy who had it built by a reputable specialist in the UK. I had not heard the engine run until I fitted it in my car, Everything looked good once I got it warmed up and timed up. I have only had it running on the drive as the car is not fit for the road yet. after 20 min of idling on the drive the engine stopped. At first I thought it was a fuel problem but when I tuned the engine over I noticed it is making no oil pressure and as I have a fuel safety switch to an electric fuel pump if there is no pressure the pump will not turn on. Before this the engine had really good oil pressure and was running ok with no smoke or knocking noises.
Any ideas what to check for, is there a way to check if the oil pump is working ?
Thanks

The oil pressure will drop fairly low at idle when the motor and oil get hot. Maybe the switch goes off at a level that is too high. Do you have a gauge? Maybe bypass the fuel pump oil pressure switch to get it running and check the pressure.

Otherwise, catastrophic oil pump failure? Or the pickup screen clogged?

Usually the fuel pumps come on right away to get fuel into the carb before one cranks it over. I'd bypass the switch as well, maybe the hot oil and the bearing clearances result in low oil pressure at idle. If you get it fired up and the pressure doesn't come back shut her down. Hard to believe a bearing would go or the pump would quit just idling for a few min.
Is there a five quart puddle of oil under the car?

If the oil pump is really not pumping, could be failure of the drive shaft from the bottom of the distributor. You can pull the distributor and check the shaft and the bottom of the distributor gear and try to turn the shaft with a screwdriver

Thanks for the help
I think I will pull the distributor as you suggested.

Update,
I pulled the distributor and all looked ok, I turned the oil pump with a drill in reverse and the oil pressure gauge showed good OP. So put the distributor back in and turned the engine over with the plugs out and again good OP. Put it all back together and it has maintained Op still not been able to drive the car but got it well warmed up on the drive and OP stayed at about 40psi at idle. I have since changed the filter and oil and hope all will stay good.
One other issue I have is when I turn the engine off I get an air hissing noise for about 10 seconds, it seems to be coming from the back of the block low down around the cranks seal. Any ideas what this could be ?
Thanks
Mark.

Before shutting the engine down remove the oil cap, see if there is excess blow-by and if the hissing goes away with the cap removed after you shut the engine down, you have too much crankcase pressure.

Ok I will try that thanks, what is the cause of to much pressure ?

Good to hear you have it running again. Did you determine if it stopped due to low oil pressure or the fuel pump switch?

Hmm, If there's combustion gasses leaking from the rear seal you'd think the rear seal would be spewing oil. Oil pan surface is on the same level as the crank maybe combustion gasses leaking from pan?

Plugged, wrong, no PCV valve?

Maybe a vacuum line bleeding (filling) after shutdown, do you have an automatic transmission?

Maybe air pocket in the water jacket or heater hose steaming off?

Oil draining back into the pan?

Combustion gasses in the cooling system?

I had excess blow by on my new engine until the rings seated and it was forcing oil past my BOP rear main seal. Just a trickle, nothing major until I got about 1,000 miles on the motor.

I had an air cleaner with twin inlets for valve cover venting so I vented both valve covers with hose in addition to the PCV until the rings seated.

It definitely wasn't showing OP on the gauge at the time, maybe the oil pump bypass valve stuck open but it seems fine now. I think I have worked out my pressure problem, I didn't have a valve cover breather that fitted so I stuck in a spare PCV valve but didnt have it connected to anything so am hoping that maybe that was stopping the engine breathing properly. I will run it with nothing in the hole and see if that stops the pressure build up.
Thanks

I had my OP gauge go to zero one day and had a heart attack, turned out it was the OP sender wasn't making a good ground connection at the threads, PHEW