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MG MGB Technical - No oil pressure reading

'71 B. Just cranked the re built engine over for the first time (Plugs out) to circulate the oil and there is a zero oil pressure reading. Checked the rockers and I can't see any evidence of oil flow. Sump is at correct level with 20/40 oil. So how long should I be cranking over the engine before I should a) get a reading or b) see oil flow around the rockers? So far I've turned it 3 times over for about 30 secs each time. Is there any way to test the oil meter or sender without pulling the dash. I notice in Haynes cct. drawing that they list both but don't show them.
Ken
K.G. Martin

Whoops, oil should read 20/50. Also it is still fairly chilly up here. Currently 10c, probably a bit less in the garage.
Ken
K.G. Martin

Ken
Did you prime the pump? If yes try a bit more. It can take a while on a rebuilt motor. If not take the pipes off the cooler if you have one and stick a funnel in the end,then fill with oil and turn the engine by hand in reverse until you suck some oil into the pump. Offhand I don't recall which pipe will suck, but you've a 50-50 chance. If that doesn't work there may be an air leak in the sump pick up pipe?
Dave
Dave Wellings

Ken,

When I did my rebuild, I ran into the same thing. I even took off the head to see if the head gasket was pluging the oil feed to the rockers. Take out the plugs, and keep spinning. It will eventually come. It just takes a while. Is your sender electric? Take off the supply line, to see if there is any oil flow. I do not remember if that dash I gave you had a oil gauge. You could rig it to see if you were getting real oil pressure.

Shareef
Shareef Hassan

Ken--pour some oil down the oil cooler hose fitting that goes into the block--the one behind the distributor. Reconnect and try it again. (Turn by hand to prime as Dave describes)Try it a few times if necessary. Other than that, it can only be an air leak at the oil pump. There's a gasket that goes between the oil pump and the block--sometimes incorrect assembly or wrong gasket is culprit. Last possibility is badly worn oil pump. Did you renew on rebuild? The specs in Haynes don't consider/address a badly scored barrel.
Paul Hanley

Thanks for the advise guys. The machine shop did say that they spun up the motor after the rebuild and that I should get pressure showing fairly quickly. The rebuild did include a new oil pump as well.However I will try priming. Your dash didn't include a gauge Shareef and mine is electric so I can't do a mechanical hook up. One thing I have just noticed is that the fuel gauge isn't reading either, so I suspect it may be electric. Of course Haynes have totally missed out the circuit for the oil system, but I will pull the dash tomorrow. (Dash cleaned up nicely Shareef) I'll keep you all informed.
Ken
K.G. Martin

The oil pump gasket is the culprit. A three-main one was used instead of the five-main one. It will suck air until you use the right gasket. Don't ask me how I know...
Al
Al McMillan

I agree with Al McMillan, having found out the same way he did. Check the gasket (it can be done with the engine in place). Good luck - Dave
David DuBois

I wouldn't get too concerned about this yet at least. You have to trust that the machine shop knew what they were doing, they did fit a new pump and said that pressure would come up fairly quickly. I've never been successful at raising oil pressure on the starter so after filling hoses there is not much you can do but start the engine! Don't let the revs rise much above 12-1500 and you should see oil pressure within 3 -4 secs. Remember the bearings would have been lubricated on assembly so do have initial protection. If all else fails I agree you may have to remove the pump and change the gasket. Fill the pump with STP at the same time and that'll fix it.
Iain MacKintosh

Ken. It took about four trys, turning the engine over on the starter for 30 seconds, then letting it sit for 20 seconds, then cranking and resting, until I got oil pressure showing on my last rebuild. I had primed the pump through the outlet at the right rear of the block.

As to not being able to get a mechanical reading because you have an "electric" gauge, this is not true. The pressure take off is located next to the output line at the upper, right, rear of the block. There is a flex line going forwards to the electrical sending unit which has a wire attached running to the oil pressure gauge. No current, a bad sending unit or a bad gauge can cause a zero reading at the dash gauge. BUT, it is easy to hook up a positive reading gauge to the block or the flex line and get an accurate reading of oil pressure. All of the later model Bs, beginning in about 72, used a direct reading gauge with the flex line going to a junction near the heater, then a hard line going to the oil pressure gauge. You can use either an original, positive reading, oil pressure gauge to take your readings or you can go to any good auto parts store and have them make up a temporary gauge using a positive reading gauge and an adapter to allow the flex line to fit it. Had one made up some 30 years ago and it is still providing good service.

As to Al's suggestion that the wrong gasket has been installed, I have seen this done even by experienced mechanics. If you are truly not getting oil pressure, drop the sump and check out the gasket. But, make sure you really do not have oil flowing before doing so. Removing the oil line at the rear of the block, then having an assistant crank the engine over is a quick, but messy, way of determining if any oil is flowing. Les
Les Bengtson

Al is right on the money! The oil pump gasket is the culprit - we had the same problem last year, replaced the gasket, cranked and got pressure.

rn
RN Lipow

I don't disagree that the gasket may be at fault. But of all of the motors I've overhauled, the MGB takes the longest to build oil pressure at initial startup. Granted I've only done two MG rebuilds. But my experience matches Les' in that it took several runs of 30 or so seconds to get pressure. And I did prime the pump through the block hole behind the distributor, as well as filling the oil cooler. As noted above, you aren't wearing anything out by running it on the starter for so long. (Except the starter itself, which is why you give it a rest periodically - to cool it down.) Everything should have enough assembly lube to protect it.
Matt Kulka

Thanks guys, but before I drop the sump, what about the fact that the gas gauge is not working either. Could there be a connection? I was going to pull the dash today - real fun now that I have the seats back in - and check wiring/voltage at the gauges. Does anybody know what the reading should be at the sender? I'll also disconnect the sender oil line to the block and turn the engine over - smaller hole, less oil. I will let you know how things go.
One other thing, I notice the fuel pump is ticking over rapidly every time I'm cranking the engine. Obviously I would expect that the first or second time, but by the 3rd and 4th I would have expected the float chambers to be full. They have been rebuilt as well. No smell of gas and the tank is full. Any ideas?
Ken
K.G. Martin

Ok, just disconnected the oil pressure sender pipe from the block and cranked the engine. There was oil flow after about 15 secs. Now it was coming out with much apparent pressure, but as it's a small bore pipe, I assume it wouldn't jet out, or should it?
I think my next test will be to rig up extension wires to my multi-meter, connect to the sender wire (White/Brown)and ground and watch for a voltage reading while cranking. Does that make sense? I'm trying to do as much as possible without taking the dash out - which means I will have to take the new seat out, which took me about two hours to put in yesterday. Sheesh!!!
Ken
K.G. Martin

Hi Ken

I still think that it is an electrical issue and that the oil pressure gauge isn't getting a signal - it's too much of a coincidence that your gas gauge shows MT when you r tank is full. I would go with Les B's approach of checking with a mechanical gauge.

All this talk about the wrong gasket has been found to be a common cause on threads in the past but may be a cause for you to worry unnecessarily. Why not call the rebuider and check if they are aware of this potential issue? They should be able to ID what they installed. It is possible that the gasket kit included both a 3 main and a 5 main gasket in which case they could check to see which one is left over.

Good luck - looking forward to that tandem drive.

Barry
73B
B.J. Quartermaine

Barry,

That's a good idea. If the machine shop are adamant that the correct gasket is fitted ask them if you should just start the motor carefully. I'm pretty sure that's what they would do and that way if anything goes wrong they would be under a moral responsibility to fix it.

Come to think of it it everything is connected up and the shop in not too far away ask them to come and start it. They really also should remove the engine and repair if necessary
Iain MacKintosh

I no longer prime my oil pumps. I do not fill the oil filter or cooler.

I do add the oil, to fill the filter and cooler, to the sump. This brings the oil level in the sump almost to the pump; almost no lift. I then disconnect (or did not connect) the line from the engine to the cooler and crank the engine until I have a solid oil flow from the line into a catch can; 10 to 15 seconds. Connect the oil line and crank another 15 to 30 seconds and you will have pressure through out the engine.

With a fresh engine, the bearings have all been lubed so the oil system is reasonably sealed and can hold a slight amount of air pressure, created as the pump pumps oil into the system. When you rest the starter, that slight air pressure pushes the oil back through the pump and you have to crank that much longer to recover. By disconnecting the line you get rid of that air lock and oil pumped into the line stays there.
Leland Bradley

Hi Guys
If I'm getting oil flow at the Sender / Block connection, then I would assume that I have oil flowing through the engine and the right pump gasket has been used.
Leyland, what you say sounds logical. So when I disconnected the sender line, would that have the same effect?
Barry, I'm with you regarding electrics, especially now that I have oil at the sender. I just wish Haynes had the oil circuit shown in the '70/71 electrical Circuit.
Keep you informed as to progress.
Ken
K.G. Martin

Ken. If you are getting oil flow from the rear of the block, you have the correct pump gasket installed. With the three main bearing engine's gasket installed on a five main bearing engine, the pump is not capable of lifting the oil to the output at the rear of the engine.

Since you checked for flow at the oil pressure take off connection, the oil has had to flow from the pump, through the oil pressure relief valve system, up to the right rear of the pump, through the line to the oil cooler (if fitted--line to the pump if not fitted), through the oil filter and into the galleys. This is an excellent indicator that the system is working properly and that your problem is either the wire, the gauge or the sending unit. I have seen all three items go bad over the years, hence, my use of the positive reading gauge to cross check readings.

I would disagree with Leyland's procedure and his reasoning. The oil pressure system is an open system with the oil pump sending pressurized oil through the galleys, after which, it drains back into the sump. Any air in the system is simply forced out of the galleys, and other parts, as a normal part of the process. Even with a closed system, such as the line from the oil pressure take-off port on the block and the flex line to the electrical sending unit or junction for the positive reading dash gauges, there is no need to loosen the flex line at the sending unit or the dash gauge (positive reading) to get an oil pressure reading. The oil will compress any air present, making such a bleeding procedure un-necessary. I should be far more worried about over filling the sump, possibly allowing the crankshaft to hit the oil in the sump and whip it into a froth, than having to bleed the system of air. Les
Les Bengtson

Hi Guys
Ok, oil gauge and fuel gauge are now working. Cause, plugging the Green onto the wrong spade terminal at the back of the Tachometer. The PO had made up a daisy chain for the earth circuit running from one gauge securing screw to the next. Seemed a reasonable idea, so when I reinstalled the dasboard, I reconnected that way. So when I came to running in the green circuit, bearing in mind that you don't have the greatest visibility behind the dash while your fitting it, without thinking I simply connected the green female to the first spade connection I saw........which was the earthing point at the back of the Tach casing!!!
Stupid cause, but brilliant fault finding!!
So, this evening I hope to make up the passengers seat and fit it tomorrow. Then, if I have time, maybe bleed the clutch to make sure the new release bearing is traveling enough, check the timing, then drop her off the chocks and see if she starts. If not I'll probably start her on Thursday. It's supposed to be warm and sunny - perfect timing.
Thanks to everyone for the suggestions and moral support.
Until the next problem,
Cheers
Ken
K.G. Martin

This thread was discussed between 26/04/2004 and 27/04/2004

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