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MG TD TF 1500 - Oil pressure question

When I first started my rebuilt engine I had about 45 pounds of pressure at idle but the pressure would only climb about 5 pound when I revved the engine. I dismantled the oil pump and found that the oil relief spring was about twice as long as the standard spring. I had the pump rebuilt and installed a new ball and spring in the oil bypass and the relief valve. Now I have 30 pounds of pressure at idle and the pressure increases by about 5 pounds when the engine is revved. since the pressure at idle is pretty good I'm wondering if the oil pressure gauge is not working properly. Any advice and or suggestions would be welcome.

Tim
TD12524
TW Burchfield

Sounds more like you had better pressure with the original spring. I'd slip the first one back in.

The oil pressure gauge is not suspect, from what you describe.
JRN JIM

Hi Tim,
Obvious question: is the feed to the flexible pipe for the oil guage from the cylinder head or from the banjo union at the bottom of the block?
Feed from the cylinder head will give low pressure readings.
Mike
Mike Christie

Mike, I should have mentioned that the feed to the gauges is from the bottom of the block. i read somewhere that the incorrect oil filter could cause the same symptoms. I'm going to try running it without the filter for a short time and see what happens.

Tim
TW Burchfield

Took out the oil filter, no difference. I installed the spring that was in the car when I purchased it and the oil pressure went from 25-30 to 40 at idle. Pressure goes to 65 when the engine is revved up. I know, leave well enough alone. The thing that bothers me is that the correct Moss spring, which is 1 1/2" resulted in such low oil pressure. But the old spring which is 2" long gave me acceptable oil pressure. I know why but I'm concerned that on a entirely rebuilt engine and oil pump the oil pressure with the correct spring resulted in such low pressure.

Tim
TW Burchfield

Tim,
Does the ball and seat look acceptable?

Bill
TD24570
Bill Brown

Bill, the old ball had a slight groove in it. I replaced it with a new ball and spring. I've since reverted to the original spring. The ball seat looked fine but I didn't have any way to examine it very closely.

Tim
TW Burchfield

Just to complicate your life, I had a similar problem.After years of trying to solve this with pump and engine rebuilds, I finaly took the gauge apart to find a blob of solder on the teeth of the curved gear that moves the gauge needle.Must have been there since it was built. After flicking off the offending solder and smoothing the tooth I now have 60lbs on cold start up and the needle moves !
A side note , I got better pressure with the original oil pressure spring than the modern replacement
Best regards, Keith
K. McKenzie

It is said that the factory would, if needed, fiddle with slightly different springs until one was found that gave a pleasing oil pressure gauge reading. The oil pressure is completely dependent on the relief valve spring. As the engine wears, and clearances become greater, the pressure goes down as wear increases. With a fresh rebuild you can set the pressure wherever you like--with that spring. Don't go too high.

BMC listed a "booster" spring aka "60/80" spring, part# 706/225. Abingdon spares sells a "booster" PRV spring.

Why your pressure does not go up much from idle RPM when revved is curious. Both springs would be used when boosting.

D mckellar

Tim,
There is a possibility that the spring rate is different than the original. For instance have a look at the image that D. McKellar posted for it shows the wire diameter is greatly different from one to the other, hence the spring rate would be different.
John...Sydney
J Walton

Keith, I will try and source a second gauge to try. Mine is the dual temp oil gauge. I had a new bulb and line put on the temp gauge and they said they cleaned the oil pressure gauge.

D mckellar, the spring that was in the car when I purchased it is 2 inches long but about the same diameter as the Moss 1 1/2" spring.

John, the spring, as I said, is the same diameter as the Moss shorter one. After replacing the spring I put more oil in the engine but forgot to replace the oil cap. I started the engine and let it idle for 15 minutes. I then revved the engine to about 4K rpm and watched a geyser of oil shoot out of the filler opening in the valve cover. So there is plenty of pressure when the engine is revving fast. BTW I did install a new rocker arm shaft and bushings during he rebuild.

Tim

TW Burchfield

The springs shown in the image of D. McKellar are used in addition for boosting pressure.

The correct size is noted in the workshop manual (if not eventually varied by the factory as posted before.

Bela

Tim, Make sure that there is no gasket between the pump head and body. The gasket goes between the pump body and the block. Don't ask me how I know. Tom
tom scott

Bela, that pretty much matches the Moss spring. But with that spring and a rebuilt oil pump and engine i was only getting 25 to 30 pounds of pressure. With the spring that was in the car when I got it (1 1/2") I'm getting 35 to 65 pounds of pressure.I need another gauge to measure the pressure to be sure of what I'm really getting.

Tom, no,the gasket is only between the pump body and the block.

Tim
TW Burchfield

With the combination of two springs the engine reaches 100...120 psi (pipe for the gauge on top of engine and compared with an external pressure meter).
Bela

Bela, that sounds like it could blow some sealing gaskets. I'm only running one spring, albeit one that is 1/2" longer than the stock spring.

Regards

Tim
TD12524
TW Burchfield

My oil pump gives me about 40 at idle, but it only goes up to about 45 when revved (maybe 50). People have indicated this is perfectly acceptable. A PO had put a sawed off bolt head under the spring originally to increase apparent pressure, but I discarded it. Along with removing the solder used to create a pinhole opening in the top oil connector to the head, I effectively lowered the pressure, but it was artificially inflated to begin with. Not sure if I want to bother with a bigger spring or anything else, because I think its mostly just altering the reading on the meter rather than improving oil flow or coverage in the engine... People also talk of reversing the take off for the oil meter to the lower connection on the engine. I did this (for a different reason, because the original lower connector was a round brass bolt with two slots, and it had gotten damage to the slots where the wrench gripped it, so I put the upper hex head connector down on the lower connection, because its hard to get at and easier to strip, so the hex head makes for easier tightening and removal in a hard to reach place) and again, while it is supposed to give a higher pressure reading it really isn't doing anything to improve oil flow, so it's a purely cosmetic change. The oil pressure is higher lower down in the engine, but what difference does it make to read 60 psi from below or 40 psi from above? I suppose it 'looks' better if you want to sell the car, but it doesn't mean a darn thing.
Geoffrey M Baker

Tim,

The other day I visited Sportsparts in Sydney to pick up some bits and pieces and during our discussion the owner brought out about 20 or so copper oil lines which feed from the bottom of the block to the head. All of the pipes had been crimped with pliers or such like to restrict the internal pipe dia. which would subsequently restrict the oil flow to the head. All had been crimped in the factory. I guess this was one way of controlling the flow.

When I previously mentioned the wire diameter of the spring it is the diameter of the actual wire and not the spring I was referring to.

My job today is to take my oil pump out to see why my pressure is too low, even after a full engine overhaul, replacing the ball and relief valve spring etc. with no appreciable effect.

John...Sydney
J Walton

Geoffrey, I believe what you read at the oil gauge (if it is working properly) is what pressure the oil is being fed to the entire system. The reason the reading at the head connection is lower is because the oil leaving that connector pipe faces little resistance. It comes out the holes and in the rocker arms in addition to the bushings. If you put a gauge on the output side of the oil filter it would match the gauge pressure. So the difference in reading 60 pounds below and 40 pounds above is that it really is 60 pounds below and 40 pounds above. The 60 pounds is a more accurate reading of what pressure you pump is putting out.

Tim
TW Burchfield

John, I don't know if you have seen John Twist's video on the XPAG oil pump but I found it very informative.

https://www.youtube.com/watch?v=ShHAaDKL3gM

Regards

Tim
TW Burchfield

True, Tim, but whether it reads 40 or 60 is just a factor of where you put the oil line. So if you keep the connection at the top you know you are reading from a lowe pressure point in the engine. So long as you understand that, you have peace of mind :)
John mentioned crimps in the oil line. Done, I imagine for the same reason as a PO or shade tree mechanic used solder to fill the end of the oil bolt, then used a tiny drill to make a small hole. Boosts apparent oil pressure - but also restricts oil flow to the head, not, in my opinion, probably the best thing to do.
I will continue to not worry about my 40-45 psi :)
Geoffrey M Baker

Tim,
Thank you for the information re John Twist's video on the oil pump. I had seen it before but it didn't hurt to revisit it again.
I took my pump out yesterday and found the end float of the main drive shaft was 0.018", far in excess of a maximum of 0.004" and a minimum of 0.002" - so it seems that this is the cause of my low oil pressure.
I will now completely overhaul the pump for there is no way I want to take it out again.
Regards,
John...Sydney
J Walton

Geoffrey/John
A bit of worthless nostalgia - when I took my newly acquired '51 TD to Ecurie Corio Geelong (Vic Australia) in 1964 for an immediate post purchase assessment the mechanic soldered closed the banjo oil fitting to the head and re-drilled at a smaller diameter. His explanation being that the rocker gear didn't require the amount of oil that was being delivered and was better being diverted to the bottom end.
Peter (TC9356)
Peter Malkin

...except you lose a LOT of valve and upper valve train cooling by reducing the oil flow...all that flow wasn't just for lubrication. Regards, tom
tm peterson

Took the oil pump to pieces today and found that it required new gears which I purchased from Sportsparts. Also, took the cover to the machine shop to have it surface ground to ensure it is flat.
I will also need to take a very small amount of metal off the end of each of the gears to obtain an end float of 0.002".
A previous owner appears to have had the body face resurfaced at sometime making the new gears slightly longer.
I will get the cover back this afternoon, re-assemble tomorrow and hopefully find an increase in oil pressure

John...Sydney
J Walton

This thread was discussed between 30/06/2016 and 04/07/2016

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