Starter Motor's

Starter Motor's are "STARTER" Motor's. They are motors that start the big motor. Enough of the jokes, yes Pat, if you're reading this I am that bored. OK, business time. When the starter switch is operated the solenoid becomes activated and the plunger us drawn in to the core by electromagnetism. This action engages the the pinion in the flywheel ring gear. At the same time the other end of the plunger the solenoid contacts move backward and creates a high current circuit which can be used to the spin the armature, through the brushes and the commutator. The pinion is connected directly to the armature and spins when the armature spins, cranking the engine. After the engine has been started, the pinion speed will exceed the starter speed. If the the starter is still in use this one way clutch will release allowing the drive to freely spin thus protecting the motor from over speeding.

There are two common types of starter motor that may be found in modern day small vehicles:

1) Pre Engaged Starter Motor:
    Basically all the writing above.
 

2) Gear reduction Starter Motor:
    Much like the pre-engaged, but is noticeably
    lighter and produces higher torque. The armature
    is located on top (where the solenoid is on the
   pre-engaged), and the pinion is moved into mesh
   by a plunger where the armature is on the
   pre-engaged (displayed in the image below)

There is a third common type around, inertia type. I didn't include it above because it is not used in modern cars, but it is being used in cars that may be still operating in older vehicles on the road today. The main difference in a inertia type is that there is no plunger or solenoid that will move the pinion into mesh with the ring gear. This is however achieved by the armatures initial movement. The force of the armature movement moves the pinion in the opposite direction to the above starter type.