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MG MGA - Alloy Rocker Cover

I recently fitted an alloy rocker cover. The original looked a bit tatty and I thought I'd spruce up the engine compartment. The alloy cover comes without a breather pipe. Does this matter? I wondered. I asked the supplier (MGOC Spares) and they said "no - the oil filler cap has a breather hole in it. Just remove hose and don't forget to plug the hole in the air cleaner."

At first sight I though this must be an anti pollution measure, burning off the fumes from the engine (a bit too advanced for MG in 1955 I think!)but there is also a big breather pipe from the cover plate on the side of the block which is open to the air.

Has anyone noticed any side effects from the loss of the rocker breather? Any thoughts?

David Marklew

Not good. The OE hose to the filter is a venting intake for the engine - the clean air from the filter goes to the engine and out the bottom, when the car is moving. The only time fumes get sucked into the carbs is sitting still. By eliminating the hose, you have made the engine unvented, and there will be problems of oil contamination and moisture build up, which is bad for engines eventually. The degree depends on how often the thing is started cold, and whether or not it ever gets up to full temp, which takes a bare minimum of 20 minutes on the road under load.
Drill the rocker cover and fit a nipple to take the OE hose.
FR Millmore

The new alloy covers I have seen recently have a very original looking steel oil filler cap (except chrome plated, with the small anti-loss retainer cable omitted leaving just a tiny hole in the center. I have no idea if this is vented to the interior, but no matter, as this hole would be far too small to allow for natural air ventillation by way of the draft tube.

The other type of oil cap might be the vented rubber cap from an early emissions equipped MGB, which has a small restrictor vent and internal filter. MGBs that used intake maniifold vacuum to apply suction to the front tappet cover would ventillate well with a small restrictor orifice in the oil filler cap. In absence of the applied manifold vacuum, the only vacuum applied to teh crankcase on the MGA is the venturi action of the draft tube, which is a very low vacuum level, so the intake vent must be large, like the hose connected to the air cleaner.

There is a low-vacuum vent kit available for an alloy valve cover. It consists of 1/2-inch hose nipple with threaded base that can be installed in a drilled hole in the side of the valve cover, and instructions on where to drill that hole. I don't recall where I saw these details, so someone may search the net to find it.
Barney Gaylord

I had a guy weld an elbow hose fitting into my non-vented cover. Works. Since I saw a cleaner similar job where the elbow was welded into the back of the cover. Less noticeable.
Steve Meline

Use one of these:

Since it is aluminum, you won't have to worry about dissimilar metal corrosion in the threaded hole. Probably wouldn't anyway due to the oil, but still. They also have angled fittings.
Del Rawlins

I have seen a fitting like this in three different locations on alloy valve covers.....
On the top, (rear), on the side, (carb side, rear), and in the rear (near the top)....
Obviously you don't want to suck oil, so what is the most efficient location, and does someone have a photo?
Edward Wesson 60MGA

Best location is on the top per the original location. This is to reduce oil being drawn into the carbs. During non-moving times, there is a small amount of blowby being taken into the carbs. The rest of the time, airflow should be the opposite direction and not an issue. The other possibility with side-mounted vent tubes is that oil in the valve train might be thrown into the tube and gravity allow it to flow down to the carbs. Vertical mounting will geive it more of an opportunity to flow back into the engine. If oily film in the carbs is not an issue to you, then any location will work. It certainly looks snazzier mounted to one of the sides.
Chuck Schaefer

I have been wondering what to do about the similar alloy valve cover that is fitted to the MGB engine in my car.

I do get a slight misting of oil from the filler cap over the top of the cover and also the engine drips oil when running. So I wonder if the crankcase pressurises a little when running, blowing oil past the crankshaft oil thrower.

The problem I have is that the carbs are fitted with long ram pipes which have individual foam type Piper air filters on them.
So there is no way of connecting a valve cover vent pipe to them.

I have found on ebay some rocker-cover vents for VW aircooled engines that look like they will fit my alloy cover.

(They are 12 a pair although I have seen them for less than 8.00). I will have to loctite or wire the fastening nut down so that it doesnt fall into the valve gear!)

I have even acquired an early MGB PCV valve system with matching inlet manifold but I have heard conflicting reports about them and so its on the "Plan B" list at the moment.

So I think I will fit the rocker cover vent into the cover, run a pipe from it down the side of the engine and fit a crankcase air breather/filter on to the end of it.

The most difficult thing has been to find some suitable "rubber" pipe with the correct bends on it so that it looks right and doesnt kink.

c firth

Here are a couple of shots that I took at car shows...
The first one runs from the back of the cover to the rear carb...I guess it could run to the front carb just as well:

Edward Wesson 60MGA

Woops!....I think it actually goes to a port in the intake manifold....I can do that, but I wonder if it has any negative effect?
Edward Wesson 60MGA

This thread was discussed between 14/04/2007 and 14/12/2013

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