The first day I ran it I noticed a lot of valve chatter. This was intended to be my break in run so I figured that once everything was lubed up the chatter would go away. This wasn't the case. After running her for about 12 minutes I let her go back to idle, at which point she died. She cranked right back up, but I shut her down for the night. The next morning I went out and started her, and I noticed my oil pressure gauge was at zero, so I immediately shut her down. I decided to pull the distributor and try repriming the pump again. After this I fired her up and the oil pressure went up, but as the motor got hotter the oil pressure dropped to nothing. This of course was from the stock sending unit, not sure what the tolerance on this thing is. After a few more tests and attempts, I verified that the oil pressure is up on initial start up, but then drops off to nothing after warm up. It only goes back up if I go above idle. I went ahead and got a mechanical gauge so I can get an exact pressure readout on it when I initially start it. On cold start she sets up right around 25-30 psi. After warm up running at highway speed, the pressure hovers right around 12-13 psi. When stopped and at idle, it sets right between 0-5 psi. I just had the oil pump and sender down, and they both looked fine, and I don't suspect an issue with them seeing that there is pressure right out the gate on a cold start. I havent noticed any rattling in the engine once I reprimed the motor and the lifters primed properly. I am at a loss at what this could be. Is it possible the pump key isnt properly seated? Im scared to death to mentio the spun bearing idea considering I am making a 1600 mile drive in 4 days. Any thoughts on what this could be? Also, I did use the engine break treatment.

 

15 psi at cruise is super low. Either your oil pump is worn out or your hemorrhaging oil somewhere. 30 PSI on a cold start still very low too.

Make sure all oil gallery plugs (if there are any) are properly plugged. Check the radiator for oil, as oil cooler failure is a fairly common problem on the 460 trucks as the age.

If all that checks out, I'd suspect improperly clearance'd main or connecting rod bearings that are leaking too much oil, or you have a worn out oil pump.

 

What was your rod and main bearing clearances when you rebuilt this engine? Sounds to me your main bearing clearances are way too sloppy .

 

Makes one wonder if all the galley plugs got put back in. If the rears didn't get in it would be leaking on the ground. If bearings where this loose I think it would be knocking. An oil pickup tube sucking air can cause this problem. Or a bad relief valve in an oil pump.