Originally Posted by Trainwreck
I got the tear down done yesterday afternoon. Not good at all, all three of the plugs under the timing cover blew out! One was found in the oil pan, one was still hanging in the hole (barely), and the third one was embedded in the crankshaft timing gear, between the rows of teeth. The crank has three of the main journals scored and all the main bearings are galled. Luckily the cam, lifters are ok. Crap! No more high volume pumps for me, gotta start gathering parts on Monday.
That's a pressure not a volume problem. The pump's relief valve is either working against excessive spring pressure that delays its opening, or the valve is hung up on a burr or chip preventing its opening. This can happen on a regular pump with exactly the same result. Without a properly operating relief valve, a stock pump or a high volume pump, either one, can develop way more than enough pressure to blow out pressed in plugs or blow up the oil filter. This valve is always what controls ultimate system oil pressure, especially if the oil is cold. You can see this in how the pressures change with RPM between a cold and hot engine. When you first fire a cold engine, new or old the pressure goes very high. Without a relief valve the pump can easily generate 100 to 200 psi depending on RPM. Therefore, a relief valve is there to set an upper limit by opening a vent to the intake side of the pump. However, as the oil heats up it looses viscosity; only then does the pressure drop off and does so drastically. You can see this if you have a sensitive enough oil pressure gauge. When you fire up a cold SBC, at idle you'll see the pressure at 60-70 psi. If you rev the engine to cruising speed, the cold pressure will stay at 60-70 PSI, because this is where the relief valve is set to open and the cold thick oil is resistant to being pushed thru the bearing clearances, so the pressure you see on the gauge is where the relief valve is venting the excess oil back to its intake side. Later, once the engine has warmed, the oil the pressure will fall back to 50-60 psi at cruise RPMs, which shows the relief valve is no longer venting oil as the pressure is now below its opening point. When you return this hot engine to idle, the pressure will drop to 20-30 psi where it had been at 60-70psi when it was cold. These numbers also move around with oil weight whether straight or multi grade. A high volume pump tends to hold a higher hot pressure at idle because it's putting more oil into the system, so you might see 40-50 psi on a hot idle which tells you the relief valve is closed. The range of difference in pressure to RPMs between idle to cruise will be smaller as the typical 60-70 psi will arrive at a lower RPM as relief valve opens against the increased volume so this will reach the relief valve's pop off pressure at a lower RPM. The system should not see a higher max pressure unless the valve's closing spring was changed to one of greater force or the bypass is not sized adequately to deal with the increased volume coming out of the pump. This of course assumes normal production type bearing clearances. If you widen the clearances and or add things like indexed oil streams onto the bottom of the pistons to cool them or behind the cam gear thrust bearing, or additional oil to sprayers inside the rocker covers to cool the valve springs, or a lot of external plumbing for remote oil filters and coolers, because these additional duties will reduce engine oil pressure and volume, requiring a higher volume pump to make up the difference in oil demand and systemic losses to passage friction. But these are things mostly done on competition engines and are seldom seen in street vehicles. The other use for the high volume pump is to keep lower RPM pressure up under high crankshaft loading like towing at highway speeds. But one has to keep in mind that all this extra oil costs power to pump and is a drain-back management problem. This really requires a good windage tray, crank scraper and pan to get it out of being whipped up where the crank is loosing power just getting thru the oil fog and the rings are swimming in more oil than they can clear off the cylinder walls.
All three galley plugs being blown out would make one think none of them were installed adequately. Especially the lifter galley plugs as they see a lot less oil than the main galley because they are feeding the upper end thru the pushrods. This was either not a correct fit diameter wise, or not installed deeply enough, and probably not staked in place after installation. The press in plugs are usually replaced with screw in plugs and Loc-Tite for anything other than stock rebuilds. But one needs to pay attention to the depth of a screw in plug on the front of the main oil galley as too long or too deep will cut off oil to the number one main.