When the ignition switch is turned the solenoid
is energized, pulling the plunger back and
pushing the drive forward at the same
time. The plunger hits the moving contact and
the motor spins. If it doesn’t, don’t scrap or
strip your starter motor yet.
Back to Basics
The starter motor engages with a gear on the
flywheel of the engine, to crank the engine, in
order to make it fire.
A solenoid is mounted above the starter. Some
purists call this bit an actuator, but no one in
the motor trade does! When the starter is
switched the solenoid pulls a plunger into
itself. The plunger is connected to an engaging
lever that in turn is connected to the starter
gear (known in the trade as ‘the drive’). So
switching the starter pulls a plunger in which
pushes the drive out into the ring gear. At the
top of the solenoid are a set of 3 contacts. One
comes from the battery, one goes to the starter
motor itself and between them is a moving
contact. The plunger (which I talked about in
the previous paragraph) comes back and pushes
the moving contact onto the others, thereby
connecting the battery to the starter motor.
This sits in a field housing (or body – yoke).
There are two types of field housing; one with
permanent magnets, the other with field coils
which are wound around ‘pole shoes’. These pole
shoes only become magnetized when a current
flows around them. Most
field coil windings can be replaced - although
they are often hard to remove because the pole
shoe screws are normally very tight indeed. The
permanent magnet version suffers more from
un-stuck magnets (which can be stuck back) - but
don't turn them round.
Broken magnets are normally caused by being
tapped with a hammer.
The commutator is usually found at the back of the armature. The brushes bear directly on this to
transfer the electrical current to and from the