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MG MGA - vent tube from carb. to valve cover

Has anyone taken the rubber hose going from the top of the valve cover to the first I did and put a rubber cap over the small pipe for summer driving. Is
it really important that this be connected to the carb.
filter? I replaced my original air filters with some chrome ones (Moss) which does not have the tube on it.
Thanks. Tom
Tom Peotter

Tom. That is part of your crankcase breather system. Designed to attempt to keep the oil in the engine which has no rear main oil seal.

Les Bengtson


As stated by Les, the tube from the air cleaner to the valve cover is an essential part of the crankcase ventilation system (as is the draft tube on the side of the engine).
If this ventilation is not present you will have a build up of a corrosive mixture of water vapor, oil vapor, and other combustion products which get past the rings, even if the engine is in good condition.
There will be an oil "sludge" formed which is damaging to efficient lubrication.

A rule to remember is that good engine designers do not add components for no reason.

Mick Anderson

The hose from air cleaner to valve cove is the air inlet for crankcase ventilation. The air outlet is the draft tube on the front tappet cover extending below the sump flange. For details on how crankcase ventilation works see here:

If you plug either of those vents you defeat crankcase ventilation, which leads to moisture condensation in the crankcase, sludge in the oil, clogged oil filter, worn bearings, black gunk on the inside of the block, emulsified oil and water condensing in the valve cover. In general it makes for polluted oil and shortened engine life.

If you plug both of those vents the engine will pressurize the crankcase and blow oil out of every possible pore and seal.
Barney Gaylord

Just adding another question to this thread..on my 1600, I have an alloy rocker cover (these covers come without breather pipes) that I tapped a pipe into to connect the hose from the air cleaner. I notice that the air cleaner gets quite saturated with oil to the extend that it eventually drips down below the normal is this?
Gary Lock

Hi Gary,

It is normal to have some oil inside the air cleaner where the breather (ventilation) pipe enters. This is mainly deposited when the car is not moving. The draught tube at the side of the engine does not create a negative pressure when the car is stationary, and hot vapours tend to exit into the air cleaner.
However, your oil deposit seems excessive. I would remove the tappet cover (item 13 in the attached image) and the tube (item 18). Clean both of them thoroughly and refit as shown.


Mick Anderson

This thread was discussed between 03/07/2008 and 04/07/2008

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This thread is from the archive. The Live MG MGA BBS is active now.