Thread: SBC Rebuilt but no oil pressure

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I completly rebuilt this 1973 350. Crankshaft and heads went to the machine shop. I boiled the block in Lye, cleaned it good and painted it up. I put new cam main and connecting rod bearings in it. New oil pump. It has .040 oversized pistons with gapless second ring. Roller rockers. Dual remote filter system with engine oil cooler. New Lifters.

When I first start it up it has 40 psi Oil pressure then drops slowly to 5 psi.

My first problem was the rear cam bearing was not pushed up against the rear cam cap. I corrected this and changed the oil pump. The plug under the rear main is there.

The fuel pump is blocked off, can I be loosing oil pressure in there?

How does the oil bypass system work? Could this be my problem?

Im using 10W30. The engine is running at 160 deg. I have a 4 row radiator. I can see through the cam bearings to the channel. They aren't precisley streight up but I can see clearly into the channel. I didn't check the bearing clearance I just used what the machine shop gave me. I did just complety switch oil pumps. Went from a high volume with a welded pickup the a stock. Neither one came with a gasket and my engine gasket kit did not come with a gasket for the oil pump. I am in the process of taking the oil pan off so I can put a gasket in there. I am using the factory gauge and when it reads 0-5 psi you can hear it in the engine.

o yea. sence the oil psi droped it never came back up. If I go out and start it now it only has 5 psi oil pressure

I've used the same machinist for about 12 years now, and I still check all his work when I get it back.......... Hope it's just something minor like Denny said.

Originally posted by canibalchicken
I completly rebuilt this 1973 350. Crankshaft and heads went to the machine shop. I boiled the block in Lye, cleaned it good and painted it up. I put new cam main and connecting rod bearings in it. New oil pump. It has .040 oversized pistons with gapless second ring. Roller rockers. Dual remote filter system with engine oil cooler. New Lifters.

When I first start it up it has 40 psi Oil pressure then drops slowly to 5 psi.

My first problem was the rear cam bearing was not pushed up against the rear cam cap. I corrected this and changed the oil pump. The plug under the rear main is there.

The fuel pump is blocked off, can I be loosing oil pressure in there?

How does the oil bypass system work? Could this be my problem?

"Dual remote filter system with engine oil cooler. New Lifters".
sure you got enough oil in the pan to fill up all those filters and extra lines?

Have you tried a different guage?

Just a thought.

Canabalchicken,
Chevy does not use a gasket between the oil pump and main cap, and not recommended to put one in it. If you pull the pan, use some plastigage and check the clearances.
Ed

Ok Hurst01. What am I checking the clearances of, the main bearings? What should the clearance be?

How does the clearances account for the first bit of oil pressure I got. 40psi.

yes plenty of oil. I primed the oil pump and got oil flowing out of all the lifters.

DennyW
could it be possible I had two different oil pumps bad and they both did the same thing?

poncho62
I have only use the factory gauge, but when it said it had 5 psi you could tell. I had some knocking and killed it right away.

You should check the clearances of the mains and rods both. This can be a serious situation. Take your time and check each one. It is possible that you could have received the wrong bearings. I was in a hurry once and did not double check eveything before installation. The crank had been turned .020 and they gave me bearings for .010. It came in a sealed kit so I fugured that everything would be correct. WRONG!!
Check each rod and each main. You definitely have a problem somewhere. 40 PSI on a fresh engine is not very much pressure in my oppinion. The fact that you only had 40 PSI at start up indicates that you have excess clearances to begin with. Excess clearances, especially in a connecting rod will let a bearing "spin" in the rod.
I don't know what your engine building experience is. Double-check to make sure that you didn't put any rod bearing caps on backwards that might have caused a bearing to spin. Personally, I prefer to go with a high volumn oil pump. I like a lot of pressure.
Just curious, did you install your cam bearings yourself?
Ed

In the process of pulling the engine back out. I will check all the bearings. I have a pretty extensive knowlage of SBC's but this is the first time I have gone this deep into one on my own. I grew up with my dad and uncles building hot rods and I've had a bunch of clunkers over the years (Lots of experance there) and some hot rods. I have replaced heads and cams on several other engines. But the first time I have had a crank machined.

I did take for granted that the machine shop gave me the right parts, it will never happen again.

I still have my high volume pump and I would like to use it. Is there anything there I should know. Like do I need a bigger oil pan? I like a lot of oil pressure too.

Thanks

o yea I got all the caps on the correct way. I stamped each one before I took any of them off.

I am still curious whether you installed your own cam bearings or not. The cam bearings have different locations that they have to be installed in and are marked to go in a certain order and have different clearances and can affect oil pressure. One bearing in particular has an oil hole that has to be lined up with a hole in the block, not a groove. I am not saying this is your problem, I just wondered if you did install them because of what you said about being able to see the groove.
As far as your question about accounting for the initial 40 pounds of oil pressure, if the engine had too much clearance and caused a bearing to shift or spin it is logical that it could cause a loss of pressure If that did happen, the pressure is not going to come back. just hope that you shut it down before it did damage to the crank.
The high volumn oil pump that you speak of, is it new? You never want to install a used pump in an engine if at all possible. I would have to awfully sure of a used pump in order to reuse it. I have been through that before. Many moons ago, I tried to save money because of a poor paying job and rebuilt an oil pump with new gears and spring. One of the worst mistakes I could have made. Wound up replacing the crank and all the bearings along with a new pump. Much too costly just to save a few dollars. you either pay now or pay later. Either way you are going to pay. It is all up to you on how you go about it.
Ed