Generally, automotive starters look similar. They have an armature housing, pinion gear housing, and a solenoid. However, internally, differences do exist based on how the starter is intended to be used. The most common variations in the three major components of the starter will be discussed.
The starter pinion gear is commonly called the bendix. However, an original starter bendix is quite different from the starter pinion gear found in later model starters. The bendix drive is a spur gear splined to a helical tube or shaft that attaches to the armature shaft. Bendix drive gears can engage the flywheel from the front or the rear. When the starter motor spins, centrifugal force causes the gear to move toward the flywheel and engage. When the engine starts, the rotating speed of the flywheel forces the bendix gear to disengage. Starters equipped with a bendix drive gear do not have a solenoid, since bendix gear engagement to the flywheel relies on centrifugal force. One disadvantage of a bendrix drive gear is that sometimes the gear will not positively engage the flywheel ring gear teeth.
Many modern day starters use gear reduction to improve the performance of the starter. These starters use less current, spin at a higher speed, and are more compact. These type of starters produce more torque to crank the engine during starting. The armature shaft has gear teeth that mesh with an intermediate gear. The intermediate gear meshes with a gear on the back end to the pinion gear assembly. The appearance of a gear reduction starter is different because the solenoid has a plunger that meshes the pinion gear with the ring gear. The forward portion to the armature shaft is geared and is not physically attached to the pinion gear assembly or shaft.
Another method of gear reduction is using a planetary gear set. A planetary gear set consists of an outside ring gear with internal teeth referred to as an annulus gear, a center gear called a sun gear, and one or more same sized middle or peripheral gears, called planetary gears. The planetary gear set is a sub assembly that usually is attached to the forward end of the armature housing or yoke. It is usually installed between the armature and pinion gear assembly.
A moveable field winding pole starter was used by Ford Motor Company from 1973 to 1990 in order to reduce manufacturing costs instead of improving mechanical or electrical benefits. This starter has a sloped steel cover attached to the outside of the yoke or armature housing. This starter does not have a solenoid attached. A starter relay is remotely located, usually on the right inner fender shield. The starter relay supplies high current to the starter motor causing the moveable pole to engage and complete the starter motor circuit. When the moveable pole engages, it also engages the pinion gear with the ring gear. This starter was later replace by gear reduction starters.
Modern day starters no longer have field windings inside the yoke. Permanent magnet poles are used in place of the field windings. These permanent magnet poles are fragile and can break easily. Using a hammer on a permanent magnet starter motor may break the magnets. Permanent magnet starters were introduced to reduce size and weight.
Finally, brushless starter motors are being used. The difference is that the permanent magnets are now moveable and the armature windings are stationary. This type of configurations would most likely require electronic circuitry.
If the type of starter can not be identified then the local auto parts stores such as NAPA, Carquest, Federated Auto Parts, Pep Boys, O’Reilly, or AutoZone would be able to identify what type of starter is in the vehicle.