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MG TD TF 1500 - Pressurising the Oil System

I have read of people "pressurising" the oil system after a complete rebuild using the priming hole - does anyone know what this means or how it is done ? I understand it pumps the oil through all holes to ensure it is where it is needed at the first turn of the motor.
D Geale

An engine is completely dry and all oilways are empty after a rebuild. There are pressure pumps to do this process, but I don't know if any are available for the XPAG engine as the threads on the priming hole are most likely British Standard Pipe or Plug. To help 'prime' the pump some suggest coating the inside of the pump with grease to so it leaks less air around the gears. The factory provided a removeable plug to put oil into the pump to help it 'prime'. That's the way I did it.
If you can't pressurize with an external pump, one proceedure after a rebuild is to remove the spark plugs, leave the ignition off and crank the engine with the starter until the guage shows some oil pressure. Then you know that all the oilways are filled, and the bearings are getting some lubrication. Quite often the cam, lifters, and valves do not get oil until full oil pressure is obtained after the engine is started. It is best to do this 'pressurizing' before the carbs are filled with fuel to help eliminate the possibility of flooding. After the plugs are inserted, some turn on the ignition and fill the carbs with fuel, and then shut off the ignition. They crank again with the ignition off to get some oil pressure, and then switch on the ignition and pull the choke while cranking. When the engine starts, watch for full oil pressure, about 40 psi or better on a fresh engine, and don't run the engine over about 1500 RPM for the first minute or so. Don't do alot of 'bliping' unless you need it to keep the engine running. There's more later, such as running the engine until hot, retorquing the head nuts, etc. Im am sure someone else will add their 'two cents' to this as some feel nothing is ever right the first time.
Blake J.

Cranking the engine to build up oil pressure is not always the best way to accomplish it. I found that long before the oil pressure built up, the starter motor was starting to over heat. The way that I got oil pressure in the engine prior to starting it was as follows. Obtain the oil fitting that goes between the flex hose and the oil pressure gauge pipe and also takes a pressure switch for a late model MGB - the one that is a 'T' (Moss P/N 2180-245). This 'T' will fit in the line in place of the one in the 'T' series cars. Get a 1 gallon pump garden sprayer at the local garden supply store and a 1 - 2 inch 1/8" pipe nipple. Fit the nipple to the third leg (female) on the fitting you just got, cut the sprayer attachment off of the hose of the garden sprayer and slide the hose over the other end of the 1/8" nipple. Pour 4 quarts of oil into the sprayer, screw the top on and start pumping. You can watch the oil pressure come right up and by the time all of the oil has gone into the engine, everything is well lubricated. Now you can crank the engine (after removing the temporary 'T' fitting and replacing it with the original one) to get a somewhat higher pressure if you want and then start the engine. I even went so far as to set up my garden sprayer such that I can attach it to my compressor so I don't have to pump the pressure up (lazy!). Good luck - Dave
David DuBois

If if takes so long to get oil pressure that the starter is getting HOT, then it's time to reprime the pump. While you're doing that, put a cold pack on the starter, or put one on even before you start. Simple, and most people have one.
Blake J.

First things first, if any who reads this and takes exception to it, contact me directly at zandor@hdc.net. Don't waste the BBS bandwith.

PART ONE
Actually there are companies that make a device of the like what Mr. Dubois describes. What it is, ias an acculimator (something like that expansion tank you have in the hot water line) that holds about a quart of oil with a manual or electric valve. When you are going to start the engine, you open the valve and watch the oil pressure. Once it shows on the gauge, you hit the starter. Does this prevent engine damage? That is open to debate. Guage indicted pressure is not the pressure in bearings. It is ljust an indicatin that oil is flowing to all the critical parts insufficient quantity.
I would serious doubt that the method of pre-oiling after rebuilding an engine that Mr. Dubois describes will fill the oil filter bowl/housing as the filter is the first thing on the outlet side of the pump. Oil is very reluctanct to gr though the piping from the oil galleries to the filter, then through the pump and into the sump. So you still have a quart of air in the system, and where will that air go when you start the engine the first time?
If you are interested in how plain bearings work as used in a car engine, here it is. Dydroplaning. When the engine stops so does the oil flowing to the bearing and the crank crashes. That is why the main and rod bearings are made out of soft metal and are replacable. It is always better to land on something soft than hard. On start up the shearability of the oil protects the bearing surfaces until sufficient oil is flowing to cause hydroplaning. This is a super simple Explanation and the need to go into the many other static and dynamic forces is a waste of bandwidth in this forum at this time.
The reason that most builders prime an oil system is so that all of the oil galleris and the filter are full of oil. On most 'v' type engines it is a very simple matter of pulling the distributor, and using a special shaft attached to an electric hand drill, turn the oil pump until oil is pumped throughout the engine. The other popular method is to REMOVE the spar (ing) plugs and rotate the engine with the starter. On a side not, if your starter gets hot (that means you can't hold your fingers on it without burning them) turning the engine over with the plugs REMOVED, then youhave a problem with either the starter or engine. Either way the pump should run until oil can be seen at the rocker ars (valve gear, cams, etc., take you pick of termonolgy or engine design). The presure gauge will show show pressure BEFORE the rocker arms will receive oil. That boys and girls is the only sure way of knowing if you have oil throughout the engine. The top end is the last to get oil and the first to run out.
ZANDOR

zandor@hdc.net

PART TWO
In rebuilding engines where there is no practical way to run the oil pump without turning the engine over, I would recommend the following proceedure:
During the rebuilding process fill the oil pump with a light weight prelube grease (and don't tell me that it will clog the oils passages because it won't). Be sure to prelube ALL bearing surfaces (mains, rods, cam,cam lobes, lifter and lifter bores, push rods [top and bottom] rocker shaft, valve tips [valve guides are done at the time of head assembly], cam chain, cam chain sprockets, crankshaft thrust bearings, oil pump drive gear, distributor drive gear, oil pump, oil pump pressure relief valve, [There is more. I know what they are, do you? Three major items and one minor.]), during the engine assembly with you favorite engine rebuilding prelube. Pistons should be well oiled when installed. Once all the big and little bits and pieces have been put in their appropriate places, and tighted to specificatins, safety wire, cotter pins, and lock tabs installed ( another discourse), you are ready to prime the lubricating system. Of course, the engine must be installed in the vehicle and all pertinent connections made, or if installed on a dyno, the fuel, exhaust, cooling systems, etc., connected. If your engine holds four quarts plus one for the filter which is five total, add one more for the oil galleries: making a total fo six. (you only need to do this once as all of the oil never drains out when you change it.) This does two things: 1) it makes it easier for the pump to draw oil from the pan to the pump, and 2) You won't have to add any oil after the first run. It won't hurt to have it a little bit over full as you will be draining it in the near future anyway according to the recommended break-in interval in you car's owners manual. Turn the engine (Spark plugs removed, remember) over by any practical means, starter, crank, hampsters, etc., until you see oil at the valve gear. When that happens, stop and go drink a cup of coffee, latte, soda, cola, un-cola, etc. Then crank again until you seel oil at the rocker arms. This is to ensure that all air is out of the oil galleries. Take another break. Check the oil level, adjust if necessary. Recheck your coolant too. Install plugs, turn on the ignition and let the carbs fill (If your fuel pump is mechanically driven off the cam as in my, OH NO, GOD FORBID, Triumph TR3, then you can forget about filling the carbs as they should be full by now.) then, DON'T PULL THE STARTER KNOB, turn the ignition off. Recheck everything you can see or adjust. Also look for leaks, especially fuel. There is no better way to ruin your day then an engine by fire. Now that you are sure everything is in order, turn the ignition on, and pull your knob: Not that one Bub! IF you have done everything correctly in your rebuilding process the engine should start in very few rotations of the crank. If the engine is reluctant to start then YOU HAVE SOMETHING WRONG!!!! Something is incorrect, out of adjustment, etc. And don't use the excuse the carbs are out of sync. Any GOOD mechanic can get the carbs very, very close to being synced and mixture adjusted without having the engine running. (If you have to ask about this one, it is time to go back to votec at high school.) It only takes three things to make an engine run, (1) spark at the right time, (2) fuel in the from of vapor in the right fuel to air ratio, and (3) compression. (All the extra verbage is for the benefit of those who like to pick nits, dot "i's" and cross "T's".) If these aren't right, then it won't start or run worse than before you started the overhaul.
Remember that modern oils are of much better quality than what was available when the XPAG/XPEG were designed, (someplace in the 1930's, I believe.) The all around performance of modern engine oils will surpass anything that was produced in the 1950's. When an engine was overhauled back then it was not uncommon to have a thick coat of sludge/goo in the bottom of the pan, and all over the inside of the engine. That was the result of oil breakdown during normal engine operation. Drop the pan on an engine today, and it will be spotless in comparison. Reasonable care in rebuilding and assembly will give you a long life without going to extemes. I would say that unless you pockets are really deep (more money than brains), or you are racing and need the tiniest edge, then there is no need for an elaborate oiling rigs.
ZANDOR

PART THREE: FINIS

Now a little trivia. On most radial aircraft engines, you don't get worried about not seeing oil pressure on the gauge until one minute after start up. That's what it is for the R1820 (1,400+ hp) and R3460 (3,200+ hp) engines, and most likely for the rest, too. Also most radial engines are mechanically blown, which increases the stresses a great deal. Some of the engines have stacked blowers, such as the R2800 used on the gullwinged Corsair. Others used a turbocharger stacked on the mechanical blower such as used on the P38 and P47. I think the P47 had a two speed blower along with the turbo. If I remember correctly, it is about half that time (30 seconds) to see indicated oil pressure for the smaller flat fours and sixes. Aircraft engines don't have very long lives as they run at very high power settings, even at cruise, in comparison to auto engines. Basicly, they are running flat out. AS used on the T28 aircrft, the R1820, at take off power, is pushing 52 inches of mercury of manifold pressure. So that is about 20 inches above standard atmospheric pressure or around 10 psi. Each cylinder of the 9 cylinder engine produces approximately 135 hp. So, if Wright and Pratt&Whitney aren't worried if the engine doesn't have indicated oil pressure in less then 60 seconds........ Oh, yeah, one other thing, in cold weather, the oil is diluted with fuel for easier starting. They have an oil dulution valve built into the aircraft. You opened it for 'X' amount of time (while the engine is running to mix it before shut down) based on the anticipated temps at start up. So why worry if you don't have oil pressure registering as soon as you hit (for TR3)(pull for TD) the starter knob? Remember that it is a long way through a small tube with, no doubt, some air in it, to the gauge. There will be oil circulating as soon as the engine starts turning over.
ZANDOR

Darcy: Bet your glad you asked that question! How fortunate that ZANDOR is a fellow of few words!
Jeff Payne

The Zandor Challenge:

1) Valve springs (they will fret on the spring seats and retainers, and the inner and outer springs rub.)

2) Timing chain tensioner shaft (I know sprockets and chain were mentioned.)

3) Distributor and oil pump shafts (Especially if re-bushed.)

4) Crank snout, before you install the gear.

5) Crank pilot bushing.

6) Distributor cam and advance weights.

7) Perhaps lube outside of valve guides w/ white lead or similar when pressing into head.

8) Timing cover lip seal if installed.

If we're talking about a long block, then of course:

8) Generator oil wick and tach gearbox.

9) Water pump grease fitting, or pack during rebuild.

10) SU throttle shafts and dashpots.
Jack Williamson

According to the MG TD/TF workshop manual you can develop an air lock in the pump it you do not remove the priming plug, and essentially bleed the oil system. An airlock will stop oil flowing around the engine. Directions for the proceedure are outlined in Section P, Lubrication P12. of the MG Workshop Manual.
Note: That after engine XPAG/TF/31263 the system became self priming and you domn't have to worry. I have personally rebuilt several engines and have never found it necessary to pump oil around the system prior to a actual start and run. Any time you have a lubricated bearing surface, make sure it is not dry.
I have used for years a magic elixar that was given to me by famous engine builder in Detroit. Assemble it with STP, a thick. very lubricious substance.

colin stafford

This thread was discussed between 03/04/2000 and 12/04/2000

MG TD TF 1500 index

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