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MG TD TF 1500 - A Fix for MGB 3-Main and 'T' series Oil Leak

What I am about to say may be old hat to the old timers but, perhaps, useful to others.

I recently had my 3-main MGB engine rebuilt. I soon discovered that it dripped oil at the rear main journal and at both ends of the oil pan in significant amounts. I suspect the main problem is that the clearance between the scroll and the block was not measured and, therefore, not adjusted to the 0.003" clearance required and the straight cork seals were not installed properly. I had plan to have these items corrected later this year.

In the interim, I was looking for a solution. Thanks to Barney Gaylord, "The MGA Guru" I discovered that a PCV valve, if installed correctly, would create a vacuum in the crankcase of about minus 2 PSI and would draw air in and prevent oil from leaking out. Low and behold it worked! The PCV valve has totally eliminated the leaks and because it is working so well I may not bother with the scroll and straight cork seal fixes.

With Barney's guidance, I used a PCV valve and related parts from a 1964 - 1967 MGB and a front tappet cover w/an oil separator from a 1967 MGB. The PCV valve and related items are available, new, from Moss Motors. The tappet cover will have to be used as they are not available new.

This idea should work for MG "T" series engines as well. The installation would be more difficult because you would have to drill and tap a 1/2 inch NPT in the intake manifold. The 1967 tappet cover will likely fit. I have not done this modification, so check it out before committing to the installation.

If I can be of assistance, feel free to call me at 843-838-0822
Frank Grimaldi

I was interested in Frank G's pcv fix for oil leaks posted several years ago. Has anyone else experimented with it and w/ what results? Also, if I understand the theory, could you put the pcv inline between the valve cover vent and the stock TD air cleaner and just plug up the tappet cover vent. This would be simpler that drilling a new connection in the intake manifold. Am I missing something?
B Roseberry

Frank....can you post some photos of how/where you put it?

Gene Gillam

Doesn't this destroy the original well planned, undocumented, feature?
Oil leaks out, so no dirt can get in.

54 TF Emma
A W Parker

Doesn't this destroy the original well planned undocumented feature?
Oil leaks out, so no dirt can get in.

54 TF Emma
A W Parker

I retrofitted one to my TD a while back not so much due to leaks but I wanted to eliminate the escape of crankcase fumes. Been working quite well.

John Quilter (TD8986)

And the opposite side of the engine.

John Quilter (TD8986)

John, it's hard to tell from the pictures (great looking engine though), does the piping from the tappet cover where the oil breather pipe used to be simply vent into the underside of the air filter cannister? If so, I'm wondering if it would work as well if it vented into the back side of a K&N pancake filter on a TD similar to the way it does on a TF?


J K Chapin

Soooo,,, what stops the vaccum from just taking air in through the breather 8 inches in front of where the pipe is installed in the tappet cover??????


Two answers:

1) The pipe from the tappet cover leads via an oil separator (the larger section of pipe which is filled with brass "wool") to a Smiths PCV valve. This valve was a common fitment to MGBs and other British cars circa 1964-69. The valve meters in the crankcase fumes with an orface and diaphragm.

2) The front vent on the tappet cover has been fitted with a cover plate with a small hole about 1/8th inch in diameter to assist in creating crankcase vacuum.

It is necessary for the PCV to tap into the intake manifold, not the air cleaner, so some vacuum is developed.
John Quilter (TD8986)

This approach must have merit I have 2 mates that have carried out this modification on both a S Type Jag and an early Wolseley. They used Subaru PCV valves tapped into the intake manifolds with connections to the sump with a baffle filter.

I must consider doing something with my TF without having to pull the motor yet again to ascertain why the Moss rear seal kit has commenced to fail.
G Evans

I've been considering doing this (not for the leak now but for fumes) but haven't yet been able to bring myself to drill & tap the intake manifold. Here's a write-up of a very slightly different way of doing it:
Rob Edwards

@ Rob Edwards. That design is what inspired me to do my conversion but I chose to drill and tap the intake manifold rather than the end core plug. As on my Morris Minor 948cc I would have preferred to place the fitting in the middle of the manifold but that is not possible on a TD due to the location of the air filer assembly.

@ G Evans. I also have a Jaguar S Type (1965) and it has the California mandated crankcase ventilation system feeding the fumes into the air cleaner just before the aluminum intake plenum that bolts to the carbs. Perhaps this was a USA only specification.
John Quilter (TD8986)

I have one on my TD and it reduced a torrent to a trickle. It does upset the idle a little but it works great. I have measured -12 mbar crankcase pressure with a U-tube Manometer at idle. Air is drawn in where oil used to leak out. It works that simple.

Declan Burns

Just to add to the above:
Here's the manifold tapping point during the test installation. I tapped both sides as the Ford Pinto PCV valve has two inlets.(The PCV valve costs~6).
A very cheap way to reduce a nasty oil leak!

Declan Burns

This thread was discussed between 22/06/2008 and 28/03/2014

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