I know this is a dumb question, but what are you're using to claimed you have build up oil pressure?I did that and it did build pressure.
I just had a similar problem today. After an oil change, I needed keep turning the engine with the starter about 4 times and for about 20 seconds each time before I started seeing pressure on the gauge. I started to get nervous. Then finally, the gauge came up slow and week at first, then on the next attempt it cam on strong. I was about to give up for fear engine damage would occur.Sounds like you had a large air bubble that had to be purged. The idiot light is rated at 4psi and valve clatter is a pretty good sign that the tappets didn't have any oil in them.
Pulling my cam sensor is a real pain in the ass! That's why when I was cranking it I was praying it would prime on its own. I have an unusual set up that makes it difficult to get to. Also, I remember the last time I tried to get it out it was so tight I just left it alone until I brought it up to Cotton's for other work. With all the accessories removed from the engine, I still remember Brian saying it was still pretty tight and had to be pryed up very slowly.Another option to prime your engine after an extended period of non use would be to pull your cam sensor and prime the engine using a drill and oil priming tool.
The least amount of disassembly, would be take off the oil filter. Pour or squirt oil into the center of the filter mount. You can rotate engine backwards half a turn or so. The oil pump will work in reverse and draw oil in. After that it should prime no prob. Also agree with removing plugs if engine is troublesome.Pulling my cam sensor is a real pain in the ass! That's why when I was cranking it I was praying it would prime on its own. I have an unusual set up that makes it difficult to get to. Also, I remember the last time I tried to get it out it was so tight I just left it alone until I brought it up to Cotton's for other work. With all the accessories removed from the engine, I still remember Brian saying it was still pretty tight and had to be pryed up very slowly.
I have a Dutweiler oil pump set-up. I was thinking that maybe if I removed the pick up from the oil pan , that maybe I could inject some petroleum jelly directly into the oil pump under pressure. I would connect a rubber hose to the AN fitting on the pump and the other end to a brand new and clean refillable caulking gun that we use for "fire stopping" in the construction business. if necessary I would have my girlfriend bump the starter a few times while injecting the petroleum jelly into the pick up.
This would have to work. No?