Technical Corner – Starter Motors

By Mark Garfitt, Club Technical Advisor

If your starter motor is lying comfortably then we will get it started, or, if you prefer, If you are sitting comfortably then I will begin.

I do not believe there is a Pre-war BMW owner who has not had problems with their Bosch Starter Motor. The amount of engagement is one thing common to them all, but have you ever looked at the black cover box on the end?

There appear to be at least two different types; my concern is with the two shown in the photograph below.

starter_motors

One of them is an irregular shaped version with a half rounded chute on one side, a protruding shield over the terminals incorporating a 5mm lip turned out at right angles. Have you ever wondered what that was all about? I have.
On the early cars with twin up draught carburettors hanging down the side of the engine they will interfere with the starter motor if it is not laid down on its side. In this position it clears everything but now being directly under the rear carburettor leaves the problem of petrol flooding over the starter; not a good combination you will agree. The chute on the cover plate, together with the extended cover with its lip over the terminals is there to provide some sort of deflection of unwanted fuel to the ground rather than mix it with errant sparks.
To use the same starter, or to be more correct the same cover, on a car where the starter needs to be in the upright position, such as used a high mounted down draught carburettor engine another problem arises. As tight as you might fasten the clamp strap you will never get the starter to lie comfortably parallel to the block, and therefore at 90 degrees to the flywheel. The reason being that the 5 mm lip will be against the block, pushing the starter out of line. The way to overcome the problem is either to change the cover to the other, later type, or simply cut the lip off. Should the starter be out of line there is a risk of it not functioning properly or at worst causing permanent damage.

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