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MG MGB Technical - oilpressure after rebuild


Having rebuilt a MGB engine, I always rotate crank
with starter motor without plugs till oil shows at the
rockers. I like the bearings to be well lubricated before starting up.

This time the oil is slow to show at the rockers and the pressure gauge normally starts to indicate pressure. This time no indication on the gauge.
Undid the union at the cooler entry. Oil showed but nothing excessive.
Any idea what I may have doen wrong?


Check that the oil pressure relief valve in the block is correctly assembled.
John H

Did you use the correct gasket for the oil pump body?
The gasket sets include 2 - one for the 3-bearing and one for the 5-bearing engine.
Both gaskets will fit, however if you use the wrong one a port in the pump is left open and oil simply returns to the sump.
Quite a few of us have made this mistake!

David Overington


Thank you for your information.

Based on your comments I started the process of elimination. Had a bad night though. As I could not reach the Pressure control valve, I have a special exhaust manifold installed, I decided to uncouple the oil line towards the Cooler.
In the block Oil was visible. So why should I not have any reading on my pressure gauge? The capilary of the temp gauge had been repaired and I checked both the functionality of the pressure gauge and the thermometer before I installed this instrument. Just imagine I did not check the narrow gauge line between the block and the gauge.
You guessed it! It was clogged. Even with 70 psi I did get any reading. I replaced this line with a new one. Everthing is dandy once again. Pressure reading on 60 psi while cranking. Will probably start the engine somewhere next week.

Thank you for your support

Frank Navest


Glad you diagnosed the problem and that it is not a rebuild issue. I remember after installing a (UK) factory rebuilt engine waiting for the oil pressure to register whilst cranking. It seemed an age but in fact came up quite quickly.

Trust that all will go well when you finally turn the key "in anger".


BJ Quartermaine


Good catch. I spent almost a year and a number of very frustrating evenings when I was getting low oil pressure on my TD. Even went to a aftermarket oil pressure gauge.

Found that my gauge and the new one were bad. Of course in my case, not until after I had taken the engine out a couple of times and spent a good bit of money having the engine looked at to assure all was well.
BEC Cunha

This thread was discussed between 05/10/2007 and 08/10/2007

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