MG Car Repair: MG Midget negative sump pressure, rubber seal kit, oil filler cap

Question
I have a 72 Midget that I have been working on for years. Had to put in a new trans and since has had a rear seal oil leak. Mechanic has put in two different rope seals and then we put in the rubber seal kit, also changed the SU carbs to a Weber Kit. How do we connect vacuum lines to achieve negative sump pressure to prevent oil leak?

Answer
Hi John,
The 72 MG Midget does not have a rear main seal, rope or otherwise. Oil that leaks out from the rear main goes to a oil slinger and drains back into the pan. The only device they used was a spiral grove cut into the crank to help keep oil back.
It is true that they used a slight vacuum in the crankcase to help stop oil leaking. If you have eliminated that system and you have some crank case pressure build up you will have oil leaks.

If there is no system on the new intake, you should consider drilling the manifold and install your own. You may have to experiment with different restrictions in your connections to get a good medium so you don't draw oil past the rings ("blow-by") too much of a vacuum in the crank case. Those Midgets when new did have a vacuum in the case so if an engine was idling and you removed the oil filler cap the RPM would raise as a vacuum leak. The trouble with the system is that it was a delicate balance and not a great system. At idle you have high vacuum and low crankcase pressure due to ring "blow-by" and at speed you have low vacuum and high ring "blow- by". This is backwards to what is needed. I think a small size vacuum supply from the intake manifold and a large pipe from the inside (between the air filter and the carburetor)to the valve cover. Would make sense.
Howard