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MG MGB Technical - Cranking oil pressure

Ive commenced the sequence of "pre-launch" activities after a long restoration - so far I've managed to get the starter running and cranking the engine, the fuel pump pumping fuel, and the oil pump primed and pumping.
Now I am ensuring oil is flowing through the engine and that pressure is building up. The gauge is showing a tad under 40psi when cranking - so I turned to the archive for advice as to what I should be seeing. A range of opinions from 50-70 psi. So I wondered if mine is too low?
The MGB Engine specs (on this site) say -
Oil pressure: Approx. 60psi. Idle at 20psi.

On this basis I am good to go to the next step of verifying timing and sparks at the plugs.

What do you think? Its a 3 brg motor by the way.


John Minchin

As long as you have any decent amount of pressure (over 20) just start it.
The amount of pressure when cranking depends on so mutch factors that you should not wory.

It can be annything ranging from a low battery, thin oil, releasevalve or slightly worn bearings.

When hot outside our GT can give oilpressure as low as 10psi but it does not use oil and runs fine delivering enough power and MPG.
So why worry.
Onno Könemann


Not sure what is meant by "restoration". Also, how long has the car not been run?

When I replaced the head on my 69 I cranked on starter as you have done and sought/gained 40 plus lb pressure as a preliminary to starting the engine. I was watching on starting to see pressure rise above that. In fact it rose almost immediately to 60lb. I would have shut her down if that was not the case.

I also crank on the starter after oil/filter change and wind her up to at least 40, though she will climb quickly to the 60lb mark once the needle starts moving. Of course there is an amount of oil retained within the engine and cooler/pipes in that case, so it is really only filling the filter that takes any time.

Having stated my experience, I'm not sure what to advise you to do. That really depends on the answer to the questions above.

Others will have views also so perhaps wait for some of those.


Ah! I see Onno is here already.
Roger T

I have had the car for 10 yrs (cringe!) and my understanding was that the motor had been given a general tidy up with new rings and bearings etc and had been run (and the car driven).
I worked on peripheral things (starter, electrics, fuel pump, radiator, carbies, steering, instruments, brakes......) but assumed that as long as i kept the engine dry and turned over by hand regularly with cylinders lubricated all would be well.

Onno, yes, the battery might be not fully charged but I wasn't worried as I was happy with the engine cranking slowly until I knew that oil was circulating.
I intend to check the compression as well as the motor is turning quite freely.


John Minchin

Remember that when you are crankiong the engine you will be lucky to get 300 rpm so oil pressure will naturally be very low. Quite frankly I'm surprised that you are getting over 10psi. Go ahead and start the engine you are in no danger at all and the pressure will soon rise as the revs go up.
Iain MacKintosh

Start it and see how it runs.
If it runs fine do not I repeat do not check compression!!!!!!!

It will only make you worry and make you invest more instead of let you drive.

Not knowing is a blessing
Onno Könemann

Almost 40 psi is great pressure on cranking over with the starter motor. If that's your biggest concern, you have nothing to worry about. Good luck on firing her up. RAY
rjm RAY

Thanks everyone, I feel happier to proceed now.
I'm naturally cautious, especially after so much time and effort - I'd hate to have to pull the engine for new bearingsat this stage!!

I'll keep you posted (but you'll hear the cheering from hear when it fires up)

John Minchin

This thread was discussed between 04/10/2011 and 05/10/2011

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