Something to keep in mind if oil pressure drops suddently.

A few days ago got a call from my son that his 94z had a sudden loss of oil pressure and needed a tow home. Apparently he was up to around 4K rpm when this happened. Luckly he had an eye on the pressure gage and the presence of mind to kill the engine before serious damaged occured.
Folllowing day:
Pulled the pan down suspecting a broken oil pump. Bearings looked good, oil pump looked good. spun engine by hand and pump shaft turned.
Second day:
Put in a new pump, just for grins, put pan back on and bolted down engine. Still no pressure.
Third day:
Removed intake manifold and pulled out pump drive gear. Gear almost completely de-thooted. Apparently what was left had enough friction to turn pump shaft with no load.
Replaced gear, put everything back & now pressure is OK.

My question. Is it common for the drive gear to strip or is this just a fluke?

 

Well, its not common. I would check everything else out. did you find any debris or anything in the oil pan. did you inspect the pump for signs it might have had debris in it that was binding it?

If oil pressure is okay, I would just watch it carefully for now.

 

well im seen this before but not in a 4th gen. i seen it in a 3rd gen. the 3rd gen had a factory roller motor in it and someone had put the wrong drive gear on it. wasnt stout enough to hold up to the roller cam. he put a bronze gear on it and it was fixed but he had driven it for a while before it did this.

my bad that wasnt the oil pump drive gear it was the distributor drive gear. my bad but i guess it happens both ways.

 

On the last post everything looked OK, but I was wrong. On a second test drive the oil pressure was OK until the engine got up to around 4000 RPM and then it would start dropping down to about 20 PSI. It would recover below 4000 RPM. Repaced oil pressure sender thinking this may have been the trouble, but this didn't help. Plumbed in a mechanical pressure gauge, same result. At this point replaced the HV oil pump with another, still no help, also noticed that oil was being pushed out of the filler tube.
Checked other web sites and where it was mantioned that the HV pump would suck all the oil out of the pan faster than it could drain back and should only be used with a large capacity oil pan, otherwise it would starve for oil. Replaced oil pump again, this time with a stock unit. Went on long test derive, oil pressure good at all speeds (20 PSI idle, 70 PSI at red line).

After 3 oil pump changes, here is what I've learned. Do not use a High Volume pump with a stock oil pan or risk engine damage when the pump drains all the oil out of the pan and the oil pressure drops. The HV pump also seems to use up quite a bit of HP as the car seems to have more grunt through the RPM range. At this point I would only use the HV pump if some additional equipment was added that would cause the need for additional oil volume, and with a large enough oil pan to keep the pump happy.

 

I learned this from a GM engineer a while back.
Minimum oil pressure for a gm small block at idle is 7 psi.
any lower and bad things happen, but at 7 psi everything will be fine.
Of course, at higher rpm the mechanical pump works harder.
The only reason to have higher is if you have tighter then stock bearing clearince.