I recentyl pulled my engine so I could replace my oil pan and timing cover gaskets. I pur everything back together,and the engine is now back in the car. I go to start it up and the thing is ticking and rattling like crazy. It sounds like there isn't enough oil in the lifters. I mocked up an oil pressure gauge and it shows that I have no pressure in the system. What could be wrong and what can I do to fix this?