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MG MGA - alloy tappet cover vent

My car came fitted with an aftermarket alloy rocker cover on my engine and I must admit that I do like the look of it.
But it is the non-vented type which worries me a little as I understand that the engine needs to flow air to through it to avoid acid and sludge build up.

I would like to fit an outlet for a vent tube into the the cover but although I can cope with most of the mechanical problems the MGA throws at me, I have no way of fabricating this or any of the thread cutting equipment necessary.

Does anyone know if if I can buy a spigot in alloy or brass that I can fit through the end of the cover to fit a vent onto?

The situation is further complicated by the fact that my carbs are fitted with long inlet trumpets ( ram pipes/ stacks) and Piper sock type air filters. So there is no filter box to fit a ventilation tube into.

So, in view of this, is it actually worth the effort?


Colyn Firth

Colyn, what you need is a K&N crankcase filter connected via a standard type rocker vent pipe to a new breather pipe on your alloy cover and then fabricate some sort of bracket to hold the filter somewhere near your front carb. It might be possible to fit a crankcase filter directly to the rocker pipe but I think it might foul the bonnet when it is closed, as there is not a lot of clearance between the top of the rocker cover and the inside of the bonnet.
Lindsay Sampford

You can install an MGB P.C.V. valve onto the inlet manifold, They fit directly into the bolt holes that hold the firing order plate onto the manifold. The heater hose union that fits into the lower radiator hose pipe is threaded so you could drill a hole into the rocker cover and hold the union in place with a nut on the inside of the cover then conect the two with rubber tubing.
I Hazeldine

Colyn, not a full answer to your problem but a vent can be added to the rocker cover by carefully filing/grinding away one of the vanes and then drilling to accommodate a new ali tube in the approximate position of the original as fitted to metal covers. Countersink the hole on the underside for welding. I took the cover to a machine shop with a TIG welder.
J H Cole

picture added

J H Cole

I thought the small hole in the vent cap(assuming the crankase vent is still in use)allowed sufficent breathing for the low miles most cars do these days

J Bray

The small vent hole (and intake filter) in the oil fill cap was for 1964-1969 models using PCV valve prior to carbon canister adsorption setup. This only works with a vacuum drawn in the crankcase.

Prior to 1964 crankcase ventilation worked by the draft tube to pulling air through the crankcase when the car is in motion. This requires a 1/2 inch unrestricted air inlet connection on the valve cover. That port should receive filtered air to avoid gunking up the crankcase. If you don't have the 1/2 inch hose connection to the carburetor air cleaner you can install a small air filter directly on the valve cover (with 1/2 inch unrestricted port).
Barney Gaylord

Thanks everyone, I have looked at fitting a threaded vent tube into the valve cover but I would prefer to use something like a spigot which has a built in flange and which would locate inside the cover with the nut on the outside.

Knowing my luck, if I fitted a nut on the inside it would no doubt, come loose and fall off inside the engine!

Barney, I have just checked out the term "draft tube" on your website and found a whole bunch of information about crankcase ventilation. (I know, I should have looked on there first!)

I didnt realise that the slipstream passing over the draft tube down by the sump creates a suction effect to draw the fumes downwards from the crankcase.
I have always assumed that it was the suction from the carbs that constantly vented the fumes upwards into the air filters.

So, once I find a suitable spigot that I can fit by just drilling a hole in the cover, I will fit a tube and a free flowing crankcase filter.
Its now on my to do list.


Colyn Firth

Colyn I knew my VW past would help a fellow MG'r. I know aircooled VW's have a following across the pond, after all it was you Brit's who saved them. Check this out, it is exactly what you are looking for-
gary starr

Thanks Gary,

that is pretty much exactly the kind of fitting that I had in mind.

I now just need to find out if I can buy these over here in the UK or if can ship one over for me.


Colyn Firth

Colyn there is a magazine called Volks World published over there,if you can find a copy I'm sure you can find a vendor who would carry those parts.
gary starr


Try VW Heritage. Its a long link so might not work properly.

Malcolm Asquith

You need to be carefull about the amount of clearance between the rockers and the inside of the cover. Anything too big and it will foul the rocker !!
All I did was drill and tap 1/4 inch BSP and screw in a barrel nipple ( basically a small piece of threaded pipe ) with a dob of Loctite. Perfect size and very cheap. Any engineering shop will do it for you.

A J Dee

Thanks Andy, I may well go that route if the breather vents dont fit.

I have sent for the screw in breather vent from vw heritage to see if it will fit.

I wonder if fitting this will reduce the crankcase pressure enough to help my drippy crankshaft oil thrower?

It would certainly make me more popular with my daughter if the car would stop dripping oil onto her newly block-paved driveway!

Colyn Firth

This thread was discussed between 16/09/2012 and 20/09/2012

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