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MG TD TF 1500 - Low oil pump pressure - 51 TD

(Starting a new thread because the heading on my last one would make it useless for archive purposes)

51 TD engine rebuild done, installed. Trying to get oil pressure. Air temp is 90 so oil is warm.

I used a garden sprayer to pump oil into the engine at the head banjo connection. (Where it also has the takeoff for the gauge).

Primed pump, filling both bolt holes on the top with oil (the lower one which feeds to the filter, and the top small one).
Made sure the oil filter was full as well.
Cranked engine for 60 seconds, twice. Got about 10 lbs pressure, nothing more.
Removed connection at head banjo, and turned engine; oil pumped out of the hole satisfactorily.

So I know oil is moving around the engine, but the pressure seems to remain low.

What are the likely causes here?
I'm thinking 1) open oil gauge, make sure oil pumps out, close gauge connection again (I did this before, and could see oil dripping out, but not spurting out).

2) Remove, strip, inspect oil pump...?

Advice welcome...
Geoffrey M Baker

Try a different gauge.
An Air pressure on is OK.

I , personally, would trust the lower connection rather than the top connection.

Jim B.
JA Benjamin

Was this same gauge reading normal values before the engine was removed? I've never seen cranking pressure from a top-mount oil pressure take-off engine. Perhaps somebody who seen this might comment on the low reading. It might be normal. Bud
Bud Krueger

Bud, the engine pressure would read about 10 lbs at idle, 40 at higher rpms. That being said, this pump has been reground and refaced and has new gears, so I would hope for a higher reading anyway.
Geoffrey M Baker

Geoffrey...

Spinning the oil pump on the engine with the starter motor is not going to give you the oil pressure you'll see when the engine is running. The fact you have oil pressure at starter motor speed is a good indication that your pump is working fine.

I don't take my pressure from the head connection though and I'm used to seeing a bit more pressure than 10 psi. Can you move the oil gauge take-off point to the block and try it there?


Gene
Gene Gillam

I wouldn't expect to get much more than that until you start it. You got oil pressure, the pump is primed. Time to light it off
W. A. Chasser Jr

Thanks all, it's a weight off my mind. Still waiting for the water pump. I'll start installing the radiator now...
Geoffrey M Baker

Geoffery -The take off point to the oil pressure gauge should be at the block end of the pipe. The point where the oil goes into the head is the lowest pressure in the entire engine, going from that banjo fitting, the oil goes into the rocker shaft and to each rocker, all of which have rather loose clearances and from there the oil just splashes down on the head and drains into the sump. Cheers - Dave
DW DuBois

Agreed, you're taking a pressure reading from a low pressure area. It's the lower end pressure that matters to the life of the engine. And I would test that gauge just to make sure it's accurate.

Air in the oil gauge pipe will not affect the reading in any way. Don't waste your time trying to bleed it. You'd have to do it every time you started the car anyway, because the line drains by gravity as soon as you turn the engine off.

40 pounds at speed is fine. The general rule is 10PSI for each 1000 RPM for a healthy engine. Flow is what you need a lot of. 65lbs would be the absolute maximum I would run on an XPAG. 50-55 is even better.

Sounds like you're fine, so just start the engine and get it over with. ;)
Steve Simmons

I second Dave and Steve totally. I was off the grid unable to post on the other takeoff position thread last week. I don't care what was original on early cars, what the pictures looked like in the manuals, or what the pressure is at the head. MG likely changed the position because the head take off was useless. Only block/main/rod bearing pressure is important to my engine's health. So hook gauge up to the block fitting and make sure that the banjo bolt has not been soldered/filled/restricted (I fought that battle once until figuring that one out). Time will tell about the slow cranking speed- mine pops up pretty high at cranking RPM. George
George Butz

I don't want to beat a dead horse, but just in case someone was not aware: the head is the correct placement for the oil gauge connection for my EARLY TD engine. You can verify this by looking at the WSM diagram A.2 if you have the correct year manual.
Later, MG changed to the lower fitting (in 1952?), presumably to obtain higher readings. But my setup and hoses only work one way : with the oil gauge fitting to the head of the engine and they exactly match the diagram in the manual.
I understand I will get lower readings by leaving this as is. That doesn't bother me in the slightest. So long as I know that my pressure reading is lower at this takeoff point, I am prepared.
Some day, I may decided to modify the OEM setup and switch, but not today.
In the meantime, I know the pump is working, having verified it by opening the top banjo and observing the flow while cranking the engine.
While waiting for my water pump to be returned (it's being modified by Butch Taras) I will move on to other areas of the engine, and reinstall the radiator next.
Geoffrey M Baker

George, how can you tell if the banjo bolt has been restricted? The upper banjo bolt on my engine has a very small orifice. I have no idea if this is original or someone reduced it... Can someone provide a picture or measurements of the correct diameter opening for the upper banjo bolt?
Thx!
Geoffrey M Baker

On the subject of moving the oil gauge takeoff...
I would add that simply switching the setup on my engine would be catastrophic. The lower round-head banjo bolt has a large orifice allowing lots of oil to pump through into the lower engine area. The upper banjo bolt which goes to the head and has the oil gauge takeoff, has a very small orifice, to reduce the amount of oil going to the rockers. One assumes this is intentional; just to reverse these would starve the big end of oil while overlubricating the head. That is what would be involved in moving the oil gauge to the bottom connection.
The only way to do it, presumably would be to purchase the correct banjo bolts for the later engine setup, as well as different length hoses and connections.
Geoffrey M Baker

I also have an early TD, with the oil pressure take-off on the upper banjo. I also had the restriction which I believed that in my case was instrumental in starving the followers for oil, leading to their untimely demise, and taking the cam with it.

I removed the restriction as it was solder that was drilled to approx. 3/32", thus allowing for more oil to go to the head, and therefore lifters. The oil pipe that leads to the head is enough of a restriction. I do read lower oil pressure at this point. I did purchase the adjustable oil relief from Moss and I set it to reflect 10 lbs/1000 RPM (hot). This was only to satisfy me.

The engine runs well and sounds as it should. I would recommend to anyone to remove the restriction, and allow for more oil to reach the head. Oil flow in my book is more comforting than pressure shown on the gauge.

My 2 cents.... CR
C.R. Tyrell

I don't see how swapping the banjo bolts would affect lubrication. The bolt does not deliver anything to the lower end. It allows oil to flow from a shared oil galley to the head. Having the small hole on top or bottom makes no appreciable difference. The bottleneck is the small orifice, no matter where it's located. What you might end up with is lower oil pressure up top, but still the same amount of flow which is what really matters anyway. Or maybe I'm thinking through this wrong.

As far as what is correct, do you consider how the car came originally to be correct, or how the factory recommends it be set up as correct? The former would require that you ignore all factory service memorandums that required dealers and repair shops to modify components when a flaw was found! For example, a service bulletin came out suggesting a TC cable bracket be cut from a triangle to an L shape. That's why most TCs have the modified bracket and all are considered 100% factory correct, even though they aren't as they came from the factory. It was a bad design that made no sense, so it was changed shortly after. And someone in the design department probably got a slap on the wrist for doing it the original way!
Steve Simmons


Geoffrey, I have 7 sets of banjo bolts and all have 3/16" approx. holes in them for oil passage. This includes top ones and bottom from 1951- late 1952 engines. All were nicely dirty and some buggered up from wrenches, so not new ones from Moss.
Richard Cameron

I second Steve.
George Butz

Steve S, does the lower banjo bolt also not feed oil to the rear cam bearing? I could be wrong, but I thought it allowed oil to the rear cam bearing as well as taking oil from the gallery to the head.
At any rate, assuming for a minute that it does not, and that the lower rear oil takeoff point exists purely to feed the head and for the oil gauge, if that is correct your statement would be true. In which case, we still have the issue of my upper banjo bolt has a pin-sized orifice and by the sound of other comments, should be enlarged... maybe... I'll need to look into this and welcome other comments.
As far as what is "correct" about the oil gauge placement, I'm sticking with what I've got because ... it works, it fits, it is in place, and it doesn't leak. If I take it apart to try to move it to the block, I run the risk of stripping the round head lower banjo bolt (already pretty stripped) opening up an oil leak from the banjos, and generally giving myself a headache. As ALL that will happen is that I will get an apparent higher oil pressure reading, I don't feel that makes any significant difference because I can always simply add 10lbs pressure in my head when I look at the gauge. The fact is that whether I put the gauge on the upper or lower fitting, there is ZERO actual change in oil pressure anywhere in the engine. I'm just getting a reading from a different place and neither place actually tells me whether oil flow is actually making it to where it needs to go in the engine.
So what I'm going to do is continue to reassemble the rest of the engine systems - cooling, generator, exhaust and carbs and get to the point where I'm ready to fire her up. When I get the water pump (still out for repairs) and it's all ready I will start her up and hopefully get her running smoothly.
Once that is done, I can look at the oil pressure issue again. If I get a consistent 20 lbs idle / 50 lbs at speed, I'll be happy. If I get less, I will consider my alternatives.
My first thought, though, would not be to move the oil gauge takeoff, but to re-examine the issue of wear throughout the engine. Should I exchange my partially rebuilt oil pump for a fully rebuilt one? What effect would a new relief spring have on the oil reading? Perhaps a new camshaft is really required?
I don't know. I'll learn as I go along...

Richard, my upper banjo bolt has a hole maybe 1/32 in size for oil to exit to the head. I'm wondering if someone closed it up to help increase apparent oil pressure to the gauge. A PO also inserted a bolt head above the relief valve spring to increase apparent oil pressure. (I have removed this).
So perhaps my head is being underlubricated and I need to fix this.
Geoffrey M Baker

If Butch worked on your pump then would tell you if it needed a full rebuild. You should be fine. A new relief spring is only needed if the old one is worn out. Or just put a shim under it. As far as camshaft wear, if you suspect a clearance issue then measure between the cam and bearing, and the size of the bearings or journals themselves. The rear two bearings will often last through several engine rebuilds but they do eventually wear. The front bearing should (in my opinion) be replaced at every rebuild regardless of condition.

The cam bearings get their oil from the galley that runs lengthwise along the side of the block above the oil pump. You can see the bulge, with fastener heads sticking out. Near the rear of the galley is a simple threaded hole so the oil can also exit there. This is where the supply pipe to the head attaches. The galley is pressurized, so oil goes everywhere simultaneously. The banjo bolt does nothing except let oil flow through it and into the pipe.
Steve Simmons


Geoffrey, Here's photo of early banjo bolts-- Holes are 3/16" approx.

Your 1/32" hole is not original, and as CR explained, your use of the restricted bolt is severely restricting the oil flow to the head and cam/lifters. Look Out!
Seems to me, Your plan to continue using your current arrangement is just ignoring everyone's experience and recommendation. I don't think your car is a one off item with a special configuration, all others have had to move the brass union fitting down on the firewall so their flex gage oil line will reach the lower banjo bolt.



Richard Cameron



Photo of Early Banjo bolt with take off adapter for gage. Also 3/16" holes.

Richard Cameron

Just don't see the problem with switching the bolts.
Gene Gillam

There isn't one. If there was a problem, the factory wouldn't have recommended it!
Steve Simmons

Geoffrey

If it helps I had the same issue as you on my 1950 TD, with the oil pressure take-off from the upper banjo. The car had been supercharged and raced like that with no apparent problem.

Having discovered the higher pressure reading available from the lower banjo I did make the change. However I chose to use a longer flexible pipe in order to retain the existing union in its place on the battery case (partly because this was where I installed a pressure alarm switch).

Tim
Tim Wilkinson

OK OK enough already :)

Bolts switched.

But I just want to say that the primary reason I did this was not to increase oil pressure to the meter, but because the round bolt (on the block) was pretty much stripped. I took it off and refiled it flat to fit a 17mm wrench, and once I'd done that I realized that it would be better to have the hex bolt (with the oil gauge takeoff) down low on the engine rather than the round bolt (because it is much easier to remove a hex bolt with six sizes than a round bolt with two slots, when it's buried in the engine... getting the round bolt off was a very difficult job!)

I also drilled out the banjo that had been filled, so both are about 3/16 through now. So I've increased flow to the head (by a very considerable amount I imagine) moved the round slot bolt to the top where its easy to get at and avoid stripping in future.
Geoffrey M Baker

Just as a point of interest in 1961 when I was 19 years old and had my first MG - a 1953 TD - I recall taking it in for a service to a BMC specialist (Geelong, Victoria, Australia). The first thing he did was fill the top oil feed bolt with solder and drill a smaller hole.
I have had my TC for 25 years and have no idea as to the hole sizes but have a constant 70psi oil pressure and drive at 4000rpm all day - 70mph - 4.625:1 Roger Furneaux diff.
Peter TC9356
Peter Malkin

This thread was discussed between 13/10/2015 and 15/10/2015

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