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Plugging Air Injection Holes

Many MGB owners are nowdays removing "clean air" emissions equipment in favor of "cleaning up" their engine compartments. Removal of the air injection pump and manifold leaves four unplugged holes in the cylinder head and plugging these holes properly is an essential part of the job.

The air injection system is usually the first to be removed in any de-smogging campaign. We soak the manifold "B-nuts" with penetrating oil overnight before making any attempts at loosening them.

With the manifold removed, the holes will have to be plugged. Unfortunately, what we see most of the time is something like this. The brass pipe plug shown here is easily found at most home hardware stores, but is not the right thread type.

We were able to remove these plugs fairly easily, but sometimes that is not the case. We've seen many improvised "solutions" for plugging air injector holes, but this is the most common.

The right way to do it:

The right type of plug is shown above. These are 7/16-20 by 1/2" long set screws and are often avalible at the same hardware stores as the brass plugs shown previously.

Shown here are two plugs installed, the left one is tightened completely while the one on the right is only started for illustration. Since these plugs are the same thread type as original, they can be installed and taken out at will. This fact allows the car to be refitted with the air injection manifold at any time should it be needed to pass future emissions tests.

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