Tractor Repair: No oil pressure, ford 8n, pressure relief valve

Question
Hey Arnie, gonna test your knowledge of Ford 8N's. I recently rebuilt my 8N. Complete overhaul, to include: Oil pump, gears, pickup tube, and pressure relief valve. No oil pressure at the gauge. New gauge, still no pressure. Took lines loose from the gauge, block, and govenor. Same results at all locations. Oil will trickle out with air bubbles. Checked galley plugs when it came back from the machine shop, still in. What can be going on. Please send help before all my hair falls out!

Answer
Hello,

  There are a lot of things that can cause no or low oil pressure.  Missing plugs or bolts, incorrect bearings, bearings installed incorrectly, relief valves installed backwards, relief valves stuck, and pickup tube suction leaks.  I have also seen oil pumps damaged while the front main bearing is being torqued if the gear teeth do not line up properly while the bolts are torqued.   Oil with air bubbles sounds like a suction leak, but that's only a guess.  Check the relief valve first.  If everything is OK, you will need to remove the oil pan and check everything.  I have heard of oil pumps needing to be primed, but that was not on an overhauled engine with a new oil pump.  They can be primed by removing the relief valve and squirting oil in the engine, then installing the relief valve.