MGB & GT Forum

6 months ago I purchased a MGB GT 1967, where the engine was completely disassembled.
Now I have assembled the engine, with all new bearings. But there is a problem, the oil pressure when starting it up is around 20 psi at 1500 rpm. I have changed the oil-pump to a new one and the oil-regulator is also new, but didn't make a difference. I use 20W50 oil, switching to a lower oil viscosity doesn't make any difference. When the oil gets warm the pressure falls to around 5 psi again increasing rpm doesn't make a difference

If I put some shims in the oil-regulator I can get bit higher oil pressure (around 35 psi), but I think there's a problem anyone, who has an idea?

Standard main bearings on a .010" under crank?

Correct oil pump to block gasket?

Gallery plugs properly re-installed?

see: https://www.mgaguru.com/mgtech/engine/of101c.htm

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Eric Russell ~ Mebane, NC
1961 MGA #61, 1981 Alfa Romeo GTV6, 1984 Alfa Romeo Spider, 1991 Honda ST1100

How are you measuring the oil pressure? You may want to confirm with a calibrated gauge connected directly to the engine. You may not want to rev the engine if pressure is actually only 5 psi. Did you hear any rod knock?

Did you use the correct gasket in the oil pump rebuild? IDK if that would give a reading like you have but figured it worth a post.

IIRC increased pressure comes from #21 here.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Lots more as I did a nut and bolt rebuild; finished 2015. Tartan Red.

GT: December '78. VW Golf guards, flush fit front and rear valances. Torana XU1 vents, frenched indicators & Mk1 rear lights. 'Worked' Rover V8 with Monsoon ECU for EFI. GM4L60E, Lokar tiptronic & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.

What were the clearances on the main and rod bearings? At the very least they should be checked with Plastigage.

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Terry Ingoldsby
terry.ingoldsby@DCExperts.com

There are no knocking sound, it sounds very normal and healthy. I swapped the pump to a new one because of the pressure, but that didn't have any effect. It is a 5 main-bearing pump whith the right gasket.



Edited 2 time(s). Last edit at 2024-04-16 09:42 AM by Janus123456.

Good point as this most often is the case in these situations. Hee's the pic of the two gaskets, I think I first shown this here almost 20 years ago.I think Dick or someone made a prettier picture than mine, so I will use the new and improved picture, LOL.

Janus this is a very common mistake. I tell folks while these pictures are good, if one was really paying attention and matched the gasket to the base of the pump we wouldn't need these pictures. Paying attention is the #1 goal when rebuilding an engine.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 1 time(s). Last edit at 2024-04-16 10:16 AM by Speedracer.

No one has asked about what oil filter was used yet.

Low oil pressure caused by failure to install new cam shaft bearings during engine rebuild.

Janus, your "oil-regulator" is an oil pressure relief valve. A properly functioning OPRV does not regulate anything but limits the maximum oil pressure near 75 psi.
You cannot reach that pressure, so the valve does not open and adding shims under the spring should not have any effect. If it does affect your oil pressure, the oil pressure relief valve could be leaking.

I have changed the Relief valve, to a completely new one, not that the old one had any problems. But could the block be damaged in any way since it isn't shutting all the way. Or should I just add a bunch of shims to see if the pressure goes to the desired level?

Bypass the oil cooler to check for partially plugged oil cooler.
Yes, it happens, as I know from personal experience.

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Pogo is right.
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The power of reasons is an illusion. The belief will not change when the reasons are defeated. The causality is reversed. People believe the reasons because they believe in the conclusion.

Read post #11 again. The oil pressure relief valve does not regulate pressure, it only prevents pressure from exceeding a set value. Its default setting is full available pressure. It starts to lower pressure if pressure gets too high. Shims will raise that threshold but unless or until pressure reaches that threshold, the relief valve isn't doing anything. This assumes it is installed correctly and is not jammed open.

In post #4 the question was raised as to how you are measuring oil pressure. Your dash gauge may be defective and your oil pressure normal. If in doubt, you need to measure pressure directly with a stand alone gauge.

Then, too, it was pointed out that there are two different gaskets used on the oil pump depending on which engine and pump you have. If the gasket or the pump are incorrect for your engine, the pressure relief system won't fix this.

If you wish to begin with the relief valve, take it out, verify there is nothing blocking the oil passages, and reinstall it, or for that matter, put the old one in if you still have it. After that, if pressure still appears low, borrow or purchase a pressure gauge (an automotive diagnostic tool not a dash gauge) and verify your pressure at the engine block. You may have 50 psi oil pressure and not know it.


GMc

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Wait for me at the gate Tuffy, because without you they're never gonna let me in.

SDCH WTCH-X Twin Oaks Tuff Nutt
2008 - 2022

Everything is possible, but I have read several times from the experienced engine builders on this site that the relief valve is rarely or never the cause of insufficient oil pressure.
You may be able to put the old one back in to see if it makes a difference, but I don't think adding shims can be the solution.