Parts of a Starter – Labeled Car Starter Motor Diagram

All 15 parts on the diagram

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The motor 8

Field frame The pole shoes are fixed inside it. The solenoid is mounted on it. It is cut through here, so it shows as a wall all round.
Pole shoes Hold the field coils against the frame. They are the cores the coils magnetize.
Field coils Current through them makes the magnetic field that turns the armature. They are seen cut, one at each end of each pole shoe.
Armature Loops of heavy copper run through its iron core. When current flows in them, the field pushes on them and the armature turns.
Commutator Each bar is joined to an armature coil. As it turns under the brushes, the right coils get current at the right moment.
Brushes They carry the current from the battery into the spinning armature.
Armature shaft The armature and commutator are fixed on it. The clutch and pinion ride on its drive end.
Bushings There is one at each end of the shaft.

Solenoid and drive 7

Solenoid Turning the key sends current to it. Its magnetic pull does two jobs: it moves the pinion into mesh and it switches the motor on.
Plunger The coil pulls it in. Its outer end is pinned to the shift lever.
Contacts A disk is pushed across the two large terminals. That happens when the plunger is pulled right in. Battery current then flows to the motor.
Shift lever It pivots in the middle. When the plunger pulls its top one way, its foot pushes the clutch and pinion the other way, toward the flywheel.
Overrunning clutch It passes the drive one way only. Once the engine fires and runs faster than the starter, it slips, so the engine cannot spin the starter.
Drive pinion Slides along the shaft into mesh with the flywheel's teeth. It cranks the engine.
Flywheel ring gear It is part of the engine, not of the starter. The pinion turns many times for each turn of the flywheel.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) US Army TM 9-8000, Principles of Automotive Vehicles, 1985, chapter 14, Starting Systems, with its figure 14-3, Typical Starting Motor, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (armature, commutator, bronze bushings, field coils, pole shoes, field frame, brushes, armature shaft, pinion, overrunning clutch, solenoid, plunger, shift lever, contact disk and switch contacts, teeth on the rim of the flywheel). (2) W. H. Crouse, Automotive Mechanics, McGraw-Hill 1980, searched in full text at https://archive.org/details/automotivemechan00crou (starting motor: solenoid, plunger, contacts, shift lever, overrunning clutch and drive pinion on the armature shaft, field frame, commutator, brushes, bushings at the drive end and commutator end, flywheel teeth). (3) Wikipedia, Starter (engine), Starter solenoid and Bendix drive, text only (solenoid, a lever that pushes out the drive pinion, starter ring gear on the flywheel, overrunning clutch, armature, field coils, brushes, pole shoes, contacts, plunger). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's starter, nothing traced. Licence: own work

How it works

The parts of a starter do two jobs. An electric motor makes the turning force, and a solenoid on top pushes a small gear into the engine's flywheel so the motor can crank it.

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The motor

The first view is the whole starter cut along its length. The armature spins on its shaft inside the field frame. Pole shoes and field coils make the magnetic field, and brushes feed current in through the commutator.

The parts of a car starter that do the cranking

The second view is the solenoid and the drive end. The solenoid pulls its plunger in, the shift lever pushes the drive pinion into the flywheel ring gear, and the contacts switch the motor on. The overrunning clutch lets go once the engine runs.

The flywheel ring gear is part of the engine. It is drawn so you can see what the pinion meshes with.
A starter generator is a different machine and has its own page.

Questions and answers

What are the main parts of a starter for a car?

A motor with an armature, commutator, brushes, field coils and pole shoes inside a field frame; a solenoid with a plunger and contacts; and a drive made of a shift lever, an overrunning clutch and a pinion.

What does the solenoid on a starter do?

Two things. Its plunger pulls the shift lever, which slides the pinion into mesh with the flywheel. At the end of its travel it closes the heavy contacts that send battery current to the motor.

What is the small gear on a starter called?

The drive pinion. It meshes with the ring gear on the flywheel. Because the pinion is so much smaller, the starter turns many times for each turn of the engine, which gives it the force to crank.

Why does a starter need an overrunning clutch?

It passes the drive in one direction only. When the engine fires and speeds up, the clutch slips, so the engine cannot drive the starter far too fast.