Dimensions of the BUKH DV20
Electric Starter Motor
In 1974 the gear rim starter replaced the dynastarter in both the DV10 and the DV20 engines. In the DV10 engine, #89157 and up had a gear rim starter. In the DV20 model, engine #93638 and up had a gear rim starter.
Notice that the starter gear is normally dis-engaged while the motor is running or stopped. When power is applied to the starter motor, a Bendix gear forces the small pinion gear to engage with the gearing on the flywheel. If you can hear the starter motor spinning and the flywheel is not turning, then your Bendix may be the problem.