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MG TD TF 1500 - 51TD oil pump weirdness

Today I got around to degreasing, cleaning and disassembling the oil pump. Some surprises there. Firstly, I followed the WM to take the pump gear off the shaft, and accomplished that easily. I discovered that there was some damage, clearly from an earlier mechanic removing the gear incorrectly, and causing gouges on the bottom where the key jammed up against it. (No really, it was NOT me).
Secondly, I have discovered that the relief ball and guide had an interesting addition: someone had placed a very short bolt (maybe 3/8 long) with a washer on top of the spring, presumably to increase the pressure on the spring. (just under the cover plug).
THIRDLY, I discovered there were precisely ZERO bypass components installed. Obviously someone took the pump out and forgot to put them in!!!
(Unless maybe they are up in the hole, but I could see them or pull them out and I fished around with a bit of wire to try to see if I could find anything).
So my question to y'all... what would be the effect on the pump of removing the bypass components while increasing the pressure on the relief ball and spring with an extra short bolt?
YIKES!
I had never looked at the oil pump before because if it aint broke don't fix it, and I had reasonable oil pressure (10 at idle, 40-50 at 2000 rpm or so).
Interesting.....
In other news, the $12 valve removing tool arrived and I was able to remove the valves and start cleaning the head.
Geoffrey M Baker

In looking further, looks like I misread the WM. I guess to access the bypass components I have to pull out a sleeve which covers those parts. So they are probably there, just still in the engine block. I'll look at that and make sure it is operational.
Geoffrey M Baker

And yes, I pulled the sleeve and the bypass components are all present. Which still leaves the question about why put in a small bolt to increase pressure on the relief spring? Does not seem like a great idea...

I also noticed on the WM pA8 that the diagram of the oil pump shows a large washer under the cover plug. I think mine is made of brass. But the book refers to a fibre washer... is there another washer in the relief valve mechanism?
Geoffrey M Baker

Geoffrey, the factory would put stiffer springs to accomplish the same thing your PO did. In and of itself, it does not hurt anything, but an unscrupulous PO might do that prior to a sale to mask a diminishing oil pressure issue indicating wear in the rotating components or the valve train. Pretty common to have wear in the rocker assembly resulting in lower oil pressure. Regards, tom
tm peterson

This deep into it you may want to start measuring clearances as you consider an overhaul. Regards, tom
tm peterson

10 at idle is adequate, 45-50 at speed is fine. If you have wear on the cover (see the archives) that could be lowering your oil pressure. Also remember to check the rocker shaft underside for wear, as it also contributes to lower OP.

Thin brass washer under the cap, not fiber - what book calls it fiber?

I've seen washers to increase the oil pressure, but never a bolt - photo>

Tom Lange
MGT Repair
t lange

If you are replacing anything, think about a later cover with the PRIMING PLUG.

Jim B.
JA Benjamin

Tom, if you read the Workshop Manual pA8 it says on the second column last para above the diagram "Care should be taken when replacing xxx xxx xxx spring and fibre washer for the plug are correctly replaced and that the fibre washer is in good condition".... In the diagram the only washer shown is the large one under the plug, and that is thin brass as you say.
I'm thinking a PO put the bolt in to improve apparent oil pressure for a sale as Tom P suggests.
Geoffrey M Baker

Let's assume for the moment that a 'unscrupulous' PO put in a little bolt to increase apparent oil pressure. I've been reading the archives and people talk about a thin shim, or even a part of a penny, to do this. The bolt head and washer alone are probably 3/16 inch thick, that seems like a LOT of increased pressure on the spring. Which indicates to me that if I ever get this engine running again, without the bolt in place, I'm going to have seriously low oil pressure at idle, and I don't want that.
Seems like the only thing to guarantee normal oil pressure would be a professionally rebuilt oil pump. Moss sells a kit. Who rebuilds these professionally? I'd like to follow up on this and know what my choices are...
Geoffrey M Baker

John Twist rebuilds them, and I believe John Seim also. The Moss instructions are quite complete - you can read them from their on-line catalog, so you can do it yourself.

Tom Lange
MGT Repair
t lange

Hello Geoffery. In the picture that is attached is the groove that the arrow points to what you are talking about as the key being jammed by a PO when assembling. If so, that groove is suppose to be there that is where the shaft is oiled from. I've seen lots of different things be used to increase the pressure. If you rebuild your pump yourself carefully measure the depth of the body for each gear, they occasionally wear differently. The washer under the cap is copper. If it's not dinged up just anneal it and use again. At one time it was hard to get the correct spring.

Butch

R Taras

Geoffrey, removal of the bolt and resulting lower oil pressure is perhaps a symptom of worn rotating parts (larger clearances). your PO could be masking engine wear not a worn pump.. In my opinion.

Since you are this far into it, have you considered taking measurements..journals/con rod big ends, main bearings and crankshaft to determine a repair/overhaul scheme or if one is needed? Regards, tom
tm peterson

Tom, that is all "in the works". I'm going to be busy doing other stuff for the next week, but I plan to pull the block and take it in, have it magnafluxed, and then spec everything!
Geoffrey M Baker

The pressure relief valve is put in an engine to prevent oil pressure from getting too high. This could happen if the oil is really cold and thick and you rev the engine way up. On one of my cars I had the relief valve stick in the closed position once and saw the oil pressure go up to 125 psi at which time the spin on oil filter deformed and started spraying oil out. When the oil was hot the pressure was 40 psi.
When the average car is warmed up and running at 2-3000 rpm the valve remains closed as all the oil is pouring through the various galleys and bearings and lubricating the engine. On a high mileage car after it's warmed up the pressure is relieved by the loose fitting bearings and the valve never opens.
You can't magically create more pressure by putting a bigger spring in the relief valve. IMHO
Chuck
cj schmit

This thread was discussed between 19/03/2015 and 20/03/2015

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