I wanted to clear up some apparent misunderstandings about the function and operation of the Bendix "drift pin" and "drift pin spring" shown in yellow in one of these images..
When discussing these parts I refer to them as "anti" drift pin and spring. Let me explain:
When the starting motor is turning and the Bendix drive gear is engaged with the flywheel ring gear AND the engine starts, the speed of the ring gear forces the smaller drive gear back along the threads of the shaft screw. When the pinion gear reaches the limit of its travel on the shaft screw threads (at the point annotated in red in both images) the head of the spring loaded drift pin drops into the smaller diameter area of the shaft screw. This retains the drive gear in the fully retracted position on the shaft screw. When the starter is again used the drive gear counter weight causes the drive gear to remain radially stationary on the fast moving starter armature shaft and pull away from the fully retracted position on the drive shaft threads overcoming the drive pin and spring tension allowing the gear to move toward the ring gear to do its job.
The purpose of the drift pin and spring are to prevent the drive gear from vibrating on the shaft screw threads and hitting the fast moving ring gear possibly causing damage.