A starter motor is usually composed of the following assemblies:
- Electric starter motor
- Engaging relay (solenoid switch)
- Drive-end bearing with single-pinion gear
The electric starter motor consists in principle of a tubular pole housing in which the pole shoes, excitation windings and permanent magnets are housed. The electrical armature with armature winding is situated in this pole housing. The engaging relay, also known as a solenoid switch, is a combination of a relay and solenoid magnet, and is mounted at the top in the drive-end bearing. The single-pinion gear with pinion, free-running roller, engaging lever, carrier and in-line spring is situated in the drive-end bearing.