I read that after a total engine strip down and rebuild it is wise to take plugs out and turn the engine on the battery for a while to build up oil pressure before starting the engine.
I did this for a considerable time but no oil pressure!! …..and repeated it but still no oil pressure. I disconnected the oil cooler pipe in the picture and using an oil can squirted oil into the engine until it backed up and also down the pipe towards the oil cooler. This oil way leads directly down into the oil pump so is able to give it a good prime.
That did the trick – on turning over the engine again there was a flicker on the oil pressure gauge. I started the engine and oil pressure immediately went up …….phew! That was a relief.