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MG MGA - Oil leak

Hi,

I have a oil leak between backplate and the oil sump, the leak is on the engine side.I pulled te transmission and it was clean and dry.The engine run for about 10 min and than it started to leak.The oil level was normal.I pulled the backplate and the cork seal under the bearing cap looked normal.Can it be the gasket between the engine and the backplate or more likely the crankshaft.I tought when it is the crankshaft, the oil is comming on the backplate on the gearbox side.
serge

Serge

Oil, like other fluids will find the easiest route to escape. In the past I have had the odd oil drip from that plate but on investigation it has come from other known 'leak' spots such as the tappet cover, vent pipe, sump plug, timing cover, etc and flowed/blasted back by the fan to the lowest point on the powertrain.

Just a thought

Steve
Steve Gyles

Serge,you don't say what engine you have. Mine is a 1500 which has the scroll arrangement behind the rear main bearing. This is supposed to 'screw' the oil back into the sump, but on my engine, and probably many others it doesn't! I have made a little box filled with 'synthetic wire wool' (a bit like thick scouring pad) which catches the drips from the engine/bell housing joint. It is attached by the two bottom engine to gearbox bolts and has a drain plug so that it can be emptied when full (it takes about half a pint). It does the trick on my car; until I forget to empty it!


Lindsay Sampford

I've managed to find the original design for the drip tray I made. It was created by C M Harter of New York, but I can't remember how I found it, as I can't see it on Barney's site but he does have something similay if you type in "oil tray".
Below is CM Harter's original text with measurements. There were two pictures, but they are part of a Word document, so they won't upload any way I know how to do. I can E-mail the document if anyone wants it


"CM Harter, New York, USA,
Here's my oil tray. It works really well. The back holes are slotted so the two lower tranny bolts can be loosened and the tray slipped in place. The tray faces forward to catch the leak between the mating surfaces of the engine and tranny. I don't have any leaks from the "giggle pin" though the next design will have a trough extending back to it. I put a piece of wire mesh in the bottom with some very coarse steel wool on top to keep any oil sloshing around though I don't think it would be a problem as long as it's drained regularly. It tray measures 1 1/4"H x 1 3/4"D x 7 1/4"W. Hope this is helpful."


Lindsay Sampford

I've found it! It is in our archive, type in "MGA Nappy"
Lindsay Sampford

In MGA there is a slot in the front side of the rear plate to allow oil to run out the bottom between rear of the block and the rear plate. This is supposed to "vent" any oil getting past the scroll seal before it gets into the bell housing. This is another designed leak point.

The scroll seal is not supposed to leak when engine is running, but would commonly lose a few drips after shut down. Unfortunately, lots of the scroll seal surfaces have been damaged over the years, usually when main bearings wear out, sometimes when a crankshaft may break.

A damaged scroll seal can leak a LOT. Proper repair requires line boring the block and probably replacing the crankshaft, and it is exceedingly difficult to rebuild and re-machine the scroll surface. If it leaks more than you can tolerate, see here: http://mgaguru.com/mgtech/engine/cs202a.htm
Barney Gaylord

I Ihave a similar problem with my mgb 3main.

One thing that can be a problem has to do with the various valve covers and air filters that are out there. If the valve cover has no breather hole on top or if the hose from the valve cover doesn't go to the air cleaner or if the breather pipe is blocked or even if the end of the pipe doesn't have the proper angle then the crankcase can become pressurized and force ooil past the various seals.
Fred H

Serge, I have lived with the same "leak" problem since I got my car 5 years ago.
My engine is also a 3 bearing MGB type which had just been rebuilt by a well known engine builder.

I have got used to the mess this causes on my garage floor, drip trays etc but although it appears like lots of oil is being lost, I dont seem to be using oil and it is rare that I have to top up the oil level.

Kens reply may have pointed out a cause that I have not really linked with the oil leak til now. My engine has an alloy tappet cover (rocker cover) which has no crankcase ventilation tube fitted and so it could be crankcase pressure build up that is causing the "leak". It also has quite long carb ram pipes (stacks)each fitted with a Piper sock type air-filter and so there is no way to feed a tappet vent tube into these.

So my next job is to fit a ventilation tube into the alloy cover, probably routing its outlet pipe down between engine and rear bulkhead.
If this doesnt solve the "leak" or at least reduce it, then it looks like a step two is to fit Lyndsay's oil catcher.

Hopefully I can then manage the leak" until I next need to take the engine out and do a proper fix then.

Colyn
Colyn Firth

Colyn, the valve cleaner vent tube must go to the carb so negative pressure is created in the engine. The metal breather pipe has an angle cut at the end which is there to create a vacuum as air passes by it.

I use K&N elements altered for the tube ala MG Guru, in the stock MGA air filters.
Fred H

When you cannot connect a vent hose to an air cleaner, you can install a small K&N breather filter to the vent port on the valve cover. Vent air is then drawn in through the small air filter before passing through the crankcase to exit at the draft tube.

The draft tube uses venturi action to create a slight vacuum to draw fresh air through the crankcase to purge the blow-by fumes and eliminate buildup of water vapor and dilution (pollution) of the oil. It is surprisingly effective, but also results in a few oil drips from the draft tube. Do not expect it to eliminate a rear oil leak, as it does not create any significant vacuum in the crankcase.

If you connect a hose to the port on the valve cover and drop it down along side the engine, you end up with two draft tubes fighting each other. You still have crankcase pressure relief, but no ventilation air flow due to no pressure differential.
Barney Gaylord

Not leaking; just marking her territory!
Russ Carnes

This thread was discussed between 14/02/2012 and 19/02/2012

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