sudden low oil pressure

[grumpyvette]

As some of you may know, I have been trying to finish my big block 454 powered 1968 nova, I installed a new set of professionally ported and polished 049 heads,and an edelbrock oval port air gap intake,and recently long tube headers.
the engine ran fine for about 3400 miles but now , I find the oil pressure down to about 12 psi at idle,with the 10w30 weight oil, So, I changed out the sensor and gauge thinking that might be the problem, but they were not!
it became apparent that the 10-12 pounds oil pressure that the gauge was showing was correct, and that there is some tapping noise in the lower rotating assembly.
This engine was assembled by a local guy who builds stock car engines. The engine is a 454 BBC with TRW pistons, and Edelbrock cam and lifters and the parts like heads i mentioned. The engine has less than 3400 miles on it, and was assembled with all quality parts.
now the oil level has never been low,and its not smoking or burning oil, so as a test We have put 20w/50 w oil in it and it runs about 40-50 PSI until it heats up,to 200f on the coolant gauge and then we are down to a 20-25 pound idle, and the tapping sounds much better but its not gone.
now what!

the 20psi of oil pressure with 50 w oil , has me far less concerned that the mention of
"some tapping noise in the lower rotating assembly" it might be something really simple like a loose oil pump pick-up, as a loose pick-up can cause low oil pressure, or a bent dip stick, or loose windage tray, It Could be something as simple as the bypass spring in the pump was left in when the oil pickup was welded on the pump, and the heat destroyed the springs temper.
but the time frame,makes me think its wear related,I can,t help but think you might have a cam lobe or lifter wear issue causing the problem, or a loose oil pump pick-up.
the 10-12 psi at idle is of less concern than the DROP in pressure over a fairly short time span, pressure is a measure of RESISTANCE to flow so a DROP in pressure indicates a REDUCTION in restriction like your bearing clearances have increased, naturally a rapid increase in clearances indicates a parts failure or excessively rapid wear.
. we ALL look at almost everything we do thru the lens of past experience, I read that post post above and the first thing that jumped into my mind was "well whats keeping you from pulling the engine and doing a careful dis-assembly and inspection, especially, the cam, lifters and bearings and oil pump, and using some plasti gauge to verify clearances, after all thats hardly a full week end job and the next weekend you can assemble it if you want too with new gaskets and if needed new bearings, honestly you will most likely find the cause is something rather simple like the oil pump pick-up tubs loose or a oil passage plugs come loose! but with out careful dis assembly inspecting and checking your simply guessing... catch it early and it should be much cheaper and easier to fix, let it continue and it may get expensive

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