Major Parts of a Starter

by Julie Durr
itstillruns article image
Car interior image by mashe from

A starter is an electrical motor that is part of the starting system of a vehicle. The starter converts electrical energy into mechanical energy to start the engine. Two major parts of a starter include an electromagnetic field and a rotating armature. Other significant parts of a starter include a solenoid, shift fork and the starter drive gear.

Electromagnetic Field Coils and Housing

A field frame is the starter housing. A core holds the starter fields in the frame with screws. Cars have two to four field coils, connected in a series. Energized by the battery, the coils turn into an electromagnet, which forces the armature to turn.


Mounted on a shaft and bearings for support, the armature is a laminated, soft iron core wrapped with a number of conductor loops or windings. On the conductor ends of the shaft are commutator bars. Carbon copper brushes held against the commutator bars transfer voltage and make an electrical contact between the frame and the rotating armature. Current flowing through the windings and commutator bars create a magnetic field which rotates the armature. The force of the rotating armature transfers through the starter drive mechanism to crank the engine.


The solenoid consists of two coils of wire wrapped around a movable core. The starter solenoid acts as a switch by closing an electrical circuit and connects the starter motor to the battery. A key inserted and turned in the ignition switch to the start position opens a current flow from the battery through a neutral switch to the solenoid. The current in the solenoid creates a magnetic field that pulls a movable core linked to the starter drive gear. The solenoid pushes the starter gear into mesh with the ring gear. When the engine starts, a clutch disengages the starter drive gear. The driver then releases the start key, which removes the battery power to the armature.

Shift Fork

The solenoid has a plunger, which pulls or pushes the shift fork attached to the starter drive gear. This engages the starter gear.

Starter Drive Gear

When the shift fork engages the starter gear, it engages the ring gear on the engine's flywheel. The flywheel, connected to the crankshaft, moves the pistons in the cylinders to start the engine.

More Articles

article divider