Hi.... I own a 1977mgb ,am having trouble with my oil presure only 20 psi on the gauge when the engine is running ,however it has been stored for 7years so needless to say it was was running rough, my question to anybody who can help is the oil presure flex which is connected to the block has som sort of electrical component between th hose and the gauge what is this for and which color wire connects to it . The car is originally from California so it is an American spec car ,I've been looking on the net for info but can't find any info , would appreciate any help could this be the cause of the low pressure ? This is my first mgb I am restoring the car from top to bottom never done anything like this before so I know very little
Gib mgb

That is a pressure switch that is part of the anti-run on system. When you switch the ignition off the switch maintains a ground circuit for it until the pressure drops below a certain level.

It doesn't have anything to do with the actual pressure or the registration at the gauge on the dash.

Jack

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I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

Thanks Jack ... it is what I thought so am I right to assume the connection is an earth cable , mgb gib

Hay Jack ...I have converted mine from rubber to chrome looks fantastic I also lowered the suspension 1inch with the moss kit living in Gibraltar its a hassle to get spares simply because they have to be imported from the uk .....will past photos as soon as I learn how to do it ..... Great site .......mgb gib.

Well, my 68, before I took it off the road, would go about 1,000 miles with new oil then the oil pressure would drop way off, to maybe 15 psi. Years later I had a machine shop tear it apart and re-work it. Still not sure if it was rings or bearings or both.
Anyway, you might want to run some heavy oil like 50wt to get the pressure and lubrication up.

You may want to drop the oil pan and clean out the sump and the oil pickup for starters. Good luck

Will do no harm ...I have also bought the spring (upgraded) for the oil pressure ...... Mgb gib

Sorry to say I bought that same spring. Made no difference. Patrick is right about checking inside the sump. I replaced the oil pump, didn't help. I'd do a compression check if nothing shows up in the nether regions.

Might start by attaching a OP diagnostic gauge to the flexline at the engine block to verify the readings. H-F has them cheap in the US, not sure about in your locale.

Ditto on the spring.

There is a considerable amount of confusion surrounding the purpose of that spring
and it has become somewhat of a pet peeve.

If your engine is building healthy oil pressure, then at high revs or when the oil is cold it would be much too high.
That spring is part of a relief valve that is designed to protect the engine from pressure that is too HIGH.

If you engine is tired with LOW hot oil pressure then that relief valve is not likely to be opening even with a weakened spring.

Installing an up-rated one, shimming the standard one, or fitting a slightly longer one will not help build oil pressure in a tired engine.

A healthy pump, that is not starved of lube, will FLOW enough oil to healthy bearings so that no metal-metal contact occurs.

When bearing clearance is excessive, gauge pressure will read low, and more importantly the wedge of oil within the bearings will fail to do its job.

Oil that is too thin, a pump that is weak or starved, or a leak somewhere between the pump and the bearings will of course also read low and may not FLOW enough oil to maintain a wedge even in healthy bearings.

Yes seldomly does the oil regulator, go bad, but I did have one stick in semi closed position one time on a race engine, it was a new cup too, and it turned out to be the oil pressue issue, so anything is possible, but my bet is you have worn rod bearings.

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Hap Waldrop
MGexperience Supporting Vendor
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Edited 1 time(s). Last edit at 04/09/2012 10:53AM by Speedracer.

Jamie, although at least rod bearings get changed when replacing rings, more than likely increasing registered pressure, the rings them selves have no effect on oil pressure.

Physically checking the pressure with a known good gauge is of course the first step.

If you establish that there is in fact good pressure right after the pump at the hose port, the only thing left on that branch would be a bad gauge.

If you do in fact have low pressure you can follow a logic tree.

The system is pressurized by the pump to deliver oil to the clearances between various working surfaces. The main ones are the rod bearing, main bearings, cam bearings and the rocker arms. There is a relief valve early on in the passages that has the oil pushing against a spring loaded slug. When the pressure reaches a certain point, usually 75+/- PSI, the slog moves off it's seat and allows the oil to dump back down into the sump thus releasing pressure to the rest of the system. As Hap says, it is rare that the slug will stick, especially in the open position, so you can fairly safely rule that out of the diagnostic tree. It is a pain in the rear to check anyway.

What is much more likely, as Hap also says, is that the larger working surfaces, the rod and main bearings, are worn to the point that the oil is easily squirting out their sides rather than being held within the confines of the proper clearance, thus offering resistance and allowing pressure to be built up. Really bad rocker bushing will cause the same effect, but they are usually an accompaniment to the other wear points.

Of course, the pump itself could be badly worn, not be capable of generating enough volume to create pressure in the first place, but checking it and dealing with it should be a part of your preparing for the worst.

If you like you could drop the pan and pull the pump for dis-assembly and inspection, but if you do that you should prepare your self for a lot of further work. If you go so far as to pull the pump you are right there staring at the rod caps and pulling one or more might reveal heavy bearing wear. One small step further is to pull a couple of main caps for a look at their bearings. If you see badly worn shells there you absolutely have your man.

The overall effect of this is that if you open things up, even just a little, and find the wear that we suspect, you are going to have to do a full, time consuming and I am afraid expensive overhaul.

Although it is a big pill to swallow now, finding the truth will be of benefit in the long run. If you continue to run the engine as it is, the chances are that you will end up really trashing a major part and the expense could be easily doubled. On the other hand, if you decide that you do want to do something and make the engine right again, it would pay great dividends to just park the thing until you can get into such a position that you can deal with it comfortably, both in finances and in time application.

Dumping heavy oil into the engine right now might be an alternative in the EXTREMELY SHORT term, like maybe getting the car home and under cover, until you can deal with all of the above, but it is not a fix.

Jack

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---------------------------------------------------- Services to Interesting British Automobiles-- www.jackscars.net ----------------------------------------------------------------
-------------I like to think that I don't service automobiles so much as I provide entertainment, fulfill dreams and revive wonderful memories --------------

I am in the northwestern North Carolina mountains, right up against the Blue Ridge Parkway. Lawn chairs are in the shop and always time to talk. Drop in any time.

What Jack say is sound advice, patching may just buy you some time. Oil pump in B series motor hardly ever go bad, and most can be cleaned up and reused, and if the sand the neck postion of the oil pump housing back flat to tighten the endflaot up, can be just as good as new pump, for example my very expensive race engine with a bunch of high dollar goodies has a good as new rebuild oil pump, that was rebuilt and modified by me for hi volume. You should alway disasseble and check the oil pump, the manual gives you the specs on this and show how to do it.

Things that cause me to thrash a used oil pump.


Deep scratches in the drive housing from not changing the oil regular

damage to the ends of the start drive, or scroll from hard debris passing thru the pump.

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Hap Waldrop
MGexperience Supporting Vendor
Make Sure to check our promotions/product offerings in the Vendor Deals Forum here.

Hi ... I finally got the engine back in , so once I've connected everything back I'll be starting it up hopefully this week , on my previous post I said I only had 20 psi oil pressure , well when I took the sump off to check the oil pump it was quite evident why there was low pressure ,the oil pump filter was clogged up with sludge and whoever rebuilt the engine used gasket cement as well as the filter and oil pump gasket and clogged everything , hopefully problem solved .... I also changed clutch, water pump, thermostat , all the hoses, oil filter pipe, oil filter ,heater valve, pressure spring, ally rocker cover, Crome bumper conversion, lowered front and rear by about 1" , total respray mg flame red, refurbished dash and dials, new moulded carpets boot as well, changed seat belts although not to happy with the way the securon seat belts fit can't find original so will have to do for now , new clutch master and slave cylinder, braided hoses thru out , new pads and shoes, all new chrome trim , new door and cockpit panels ......and probably some other stuff to much to remember , as you can probably tell a whole load of money , so I told the wife in times of such hardship and people struggling it wouldn't be fare to go on Holliday , so she's now on Holliday and I'm going to finish car in peace .

Mgb gib

Brian,
It's great that you FOUND something and it was not terminal.