What the drawing doesn't show is what happens INSIDE when the distributor has a jillion miles on it, things get worn, and the engine runs a bit wonky.
Note the drive gear at the bottom of the distributor shaft. Just above it, where the shaft passes into the distributor housing, the housing itself wears, because Bosch did not see fit to install a bushing there.
Here is how to test YOUR gesparker to see how bad that wear is, down at the bottom of the housing.
Take off the distributor cap and the rotor, rotate the engine until the ignition points are OPEN, then push the center shaft toward the point, as I show here.
This is a drawing of the cam on the center shaft, and the ignition points [the points gap should be 0.016"].
Watch the points gap. Push on the center shaft. If the gap increases more than about 0.004", the wear at the bottom means the housing will have to be bored and bushed.
The drawing below shows the distributor parts. Another malady of distributors is a bad diaphragm in the vacuum chamber [shown by the unnamed arrow]. Put a hose on the pipe to the chamber and suck on it. The breaker plate must rotate anti-clockwise as you suck on it. If it does not rotate, the diaphragm has a hole in it and the vacuum control unit must be replaced.The good news is the distributor can be reconditioned and new vacuum control units are available.
