Heavy Breathing

Heavy Breathing

Q Can help with an issue I have with the engine breathing system on my 1275 Midget? At the moment, when the engine is between cold and warm the inlet sucks up a slug of oil through the breather, coughs it out through the exhaust in a huge cloud of smoke, clears and then is fine until the next start up. It’s a 1970 model, so has the crank breather straight to the Y piece on the carbs.

The engine is a replacement from a reputable engine remanufacturer (I had the same problem on the old engine) and has a small amount of negative pressure if you take the oil filler cap off to test. The cap is also new. I’ve trialed it with a catch can between the crank and carbs, which ticked the box with the smoking but has the effect of increasing oil leakage and fills up at a rapid rate. Apart from that, the car runs well.

A This is a common issue on 1964 and newer cars. That date was when legislation first dictated that engine fumes ‘must pass through the combustion chamber before being allowed into open air’ and created the closed circuit breather system. Two types apply to our classic MGs. The 1964-1969 one with a mushroom shaped valve on top of the balance pipe of the inlet manifold has a spring loaded valve inside sealed with a moving rubber diaphragm and was never that reliable, suffering commonly from splitting diaphragms and then later wear in the moving valve sections.

The second type is the 1969-on format where the valve was replaced by a very simple small drilled hole through each carburettor body into the airstream being drawn into the engine, the breather hose now running directly to a Y piece and then a hose to a stub on each carb where the holes were located. Having lost all moving parts, this later system could only fail if the small holes ever became blocked, and if so cleaning out was very simple.