I have a 72 gmc truck with a 350eng and have very low oil pressure,so I changed the oil pump and it did good for a while and then it started to go low.I couldn't find where any oil was leaking,also when I'm driving it sounds like the rocker arms are not getting any oil because you can hear them as if there's no oil being pumped.so could any one give me a clue on what

Thank u

Because of the age of the engine, journal wear is likely a major factor. Sludging is another possibility. Attach a mechanical oil pressure gauge and get a reading. You are probably facing a rebuild, since you already replaced the oil pump.

If you have just rebuilt the engine, perhaps you have blocked an oil way to the rockers.

You should have provided that material information. I suspect, more than ever, that journal clearances are off. There are rebuilds and there are rebuilds.

In a high mileage engine, low oil pressure is often due to a combination of worn main and rod bearings and crankshaft journals. The oil pump itself does not create pressure. It produces flow and the resistance to that flow produces pressure. Resistance is created by the orifices in the engine block through which the oil flows, and the amount of clearance between the bearings and crankshaft journals. As the bearings wear, clearances increase allowing increased flow which reduces pressure.

Okay, so you already knew that. But what you may not realize is that it doesn't take much of an increase in bearing clearances to cause a noticeable drop in oil pressure as well as noise. This applies to brand new engines as well as high mileage ones.

Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can cause up to a 20 percent or greater drop in oil pressure, which may in turn have an adverse effect on lubrication elsewhere in the engine (such as the camshaft and upper valvetrain, especially in overhead cam engines). Whether the excessive clearances are due to normal wear or "loose" assembly tolerances makes no difference because the result is exactly the same. Excessive bearing clearances will also increase engine noise and pounding, which over time can lead to bearing fatigue and failure.

Valves are last on the oil train and the first to go. The dangerous rocker arm sound you are hearing will shortly, if not already, damage the cams, rods, valves, and crankshaft.

Keep us posted.