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MG MGB Technical - 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

Frank

Does the engine number on your engine commence GUH or GAUH?

As I understand the GAUH engine had the PCV valve fitted as standard where the GUH engine, which is the earlier version did not.

Ian Buckley

There is an old boy up the road from me with a TC with a newly rebuilt engine. He assures mr that he spent half a day scrapping in the rear sealing ring!!

Guess what he has a serious oil leak.
Please explain to me what a PCV valve is??

Colin


Colin Parkinson

Colin,

I believe they are refered to in the UK as gulp valves. PCV stands for Positive Crankcase Ventilation.
In the USA it's more often than not a spring loaded valve that sets in the valve cover with a port that runs to the carb. At idle and low vacum it remains closed but at open throttle it allows the crankcase gases to be drawn into the carb for burning. I feel for your friend with the TC. I took care of the rear seal on my TF with the Moss conversion which to this point has been trouble free.

LaVerne
LED DOWNEY

Ian,

My engine identification plate is missing so I can't tell you the engine number. I am pretty sure that it is a 18G or 18GA.

Frank
Frank Grimaldi

LaVerne,

I think they refer to the PCV valve as a breather valve in the UK, not a gulp valve. The only time I have heard of gulp valve is in the US for the one-way valve preventing exhaust blowback into to the emissions air pump.
FWIW, Ed
Ed Brorein

Frank

I was just going to make the point that GUH engines which were the early 3 bearings, did not have the PCV valve but the GAUH engines did. My car is 1964 and did have the PCV valve. I have had my car for forty years and for 35 of those years it had the 3 bearing motor and I had rear main oil seal problems.

When I totally reconditioned a spare engine in 1978 it leaked at the rear and I dismantled the engine and had the block tunnel bored and some white metal laid adjacent to the scroll to reduce the clearance but it never worked totally. My scroll had been slightly damaged earlier in the engine's life, but otherwise the crankshaft was perfect and I had the entire engine balanced so I had to tolerate it.

I would imagine that the PCV valve would help and this may be one of the reasons they were fitted.

I was trying to find a picture of how the early PCV valve looked but I was unable to find one.

cheers
Ian Buckley

Frank, your engine would have been 18G. The 18GA engines were equipped with a PCV valve, and related changes, such as new valve cover, front tappet chest cover, etc. It is the major difference between 18G and 18GA.



Paul K

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

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