Robert61

This is 100% true and fact. If the plug is left out you will still have pressure but the oil will not be forced through the filter.

Robert61

About the only thing I can think of that would cause this is the center plug above the cam might have come out or been left out initially. Remove your gage and turn the priming tool to verify oil flow. I was priming and setting the oil pressure on a big block a few years ago and it wouldn't build very much pressure. I had the pan off of that thing several times messing with the bypass spring. Nothing would change the pressure. I was about to tear into it when I changed the gage. The old gage was bad, new gage good oil pressure. I would suggest putting compressed air in where the gage goes and listening for air escaping in the engine. I have a friend that is bringing me his LS motor today. it started out with lifters ticking. They changed the lifters and told me it only had 7 lbs of oil pressure. I told them a procedure to eliminate the bad oring in the pick up tube but they went straight in and changed the oring and pump. Big job on an awd as the front axle has to be dropped. Still 7 lbs. I told him the only thing that would cause this is a cam bearing has migrated out. Put air pressure to the system and listen for air. They did that and heard air. Turns out number 3 cam bearing came out. I'll be trying to fix it in the next week.

vettsplit 63

You don't say whether or not you had the crank turned, but I helped a friend who was rebuilding his bbc one time, and he had low oil pressure that went to almost nothing when the engine would warm to operating temperature. Even went to a high pressure pump with not much improvement. I had him pull the pan one more time and checked the mains. He had put standard main bearings with a .010 under ground crank. Wouldn't even touch the Plastigage. Changed those carefully one main at a time with the crank in it, and it instantly went to 60 lbs. cold.

jimh_1962

I had a similar problem with a faulty oil pump...

Basically, I was getting around the same amount of oil pressure as you are seeing.

The drill seemed to run easily when I primed the engine. I did not take notice that there was not a lot of oil coming through the rockers. I overlooked the problem during the priming process.

5-7 lbs was the highest reading I had seen during the startup. So I pulled the engine out and checked the clearances and cam plugs once more. Really, I knew nothing had changed other than oil pump. I had bought a melling low pressure pump to replace the high pressure high volume pump I was originally using. The oil pump was basically the only thing I had changed. Not to go into but was trying to address another problem for the reason to work on the engine (head gaskets and head work).

The drill should be working hard (getting hot) to move the oil upwards during the priming process.

Things to check:
1. Check the oil pump pickup is at the correct height. No Oil = No oil pressure.
2. Install a oil pressure gauge when you prime the engine.
3. Replace the oil pump.

Ol Blue

Some early sbc engines needed an oil groove in the rear cam journal or it would not get oil pressure. Long shot I know as I think 57 was the last year for that.

Robert61

I just remembered one other scenario. Several years ago I had an engine shop. I rebuilt a 2.5 liter gm engine. The shop calls and says it has oil pressure until it starts and it immediately falls to nothing. They removed the pan and brought me the pump. When they pressed the drive shaft into the gear in the pump the gear split. It would hold enough to make some pressure and then start slipping back to zero.

Westlotorn

You might take a good look at John Z's picture as posted and look at the plug location for the main oil feed. If that plug is not up far enough it could block all oil. John's picture gives you the proper distance from the main cap surface to the plug. Pull the rear main and verify. The pan is off so that is only a couple more bolts and its out.
It will be something simple, you just need to locate the issue.

Robert61

The hole is larger than the plug until it gets to where it needs to be. Then it becomes press fit.

MOXIE62

A few years back I did one of the stupid things ever. I removed can to replace filter. Had to go to work so I did not put can back on and decided I would do it in a couple of days. Well you can probably guess, I went out to shop, hopped in car, and turned engine on. Before I knew it the whole floor was flooded with oil. I quickly turned engine off. Cleaned up mess, refill oil and engine ran fine. I guess the point of this story is I would run it for a few seconds and see if oil gauge comes up. Did not hurt my engine.

MikeM

I was thinking of suggesting that the gear could be slipping on the pump shaft. Never seen it but it's possible and fits what's happening here.

jim lockwood

Absolutely. And I say that (well.... write it..) from first hand experience.

SledgeHammer 2.0

Cool, A man with a plan. Let us know what happens.

W Guy

This is great advice and a good trick. It'll save the time & trouble of opening up the lower end and removing the main cap. Just make sure you see oil pouring out of the side hole and not just the center. (see John's diagram.)

Verne

autoalain

folks, machine shop forgot to put in the 3 little oil plugs in back of timing chain. and I forgot to check(comes with age I guess), problem solved and THANKS to all for input..Mike,

cardo0

Thanks for the feedback. IMHO feedback is as valuable to those trying to help as much as fixing the problem for the OP.

JohnZ

Thanks for the feedback! Had one like that come through my shop 10-12 years ago; 3 holes, no plugs.

kolsen911

My first engine rebuild years ago. Bought a bare block from a friend. Built the engine and no oil pressure. Turned out the freeze plugs behind the timing gear had been removed and I didn't see them missing hence no oil pressure, jeez!

Randy G.

Good find!

BADBIRDCAGE

Refer to post 7.

Westlotorn

I agree, that's why it was in post #5👍