12-Volt Starter MotorBy Elina | Published on Dec 03,2015
If you've ever tried to turn an engine manually to line up timing marks, you know that pushing eight cylinders through their compression stroke is a monumental task. Multiply that task many times per day, through hot and cold weather, turning the engine between 85 and 150 RPM to allow ignition to take place, and you begin to understand the technological wonder that is the electric starter.
The bulk of the electric starter is a relatively simple 12-volt (or six-volt) electric motor. Connected to that motor are the two parts that make it a starter: the pinion gear and the bendix assembly. When the electric starter is activated, either via a key switch or a floor-mounted switch, the starter bendix senses the armature momentum and forces the pinion gear to extend into the teeth around the circumference of the flywheel. Once the engine has started and the ignition key has been released, the bendix loses momentum and the bendix is forced to return to idle position.
The electric starter is contained within a heavy-duty starter housing, which is designed to withstand the forces generated by the starter motor turning the engine through its cycle. The housing also contains the armature magnets, which surround the armature assembly including the starter windings, and a brush set that is used to contact the armature to transfer electrical energy.
The electric starter draws tremendous amperage during a start cycle. If you were to run that power through a conventional switch, it would short-circuit almost instantaneously. To cope with these heavy amperage draws, electric starters use a starter solenoid as the main power switch. Most starter solenoids are attached to the starter motor housing itself. Some are constructed in such a way that the solenoid can be removed and replaced separate from the starter motor, but most will require replacement of the entire motor. For many years, Ford products used a separate starter solenoid mounted to the fender or firewall, which could be replaced independent of the starter motor.
There are a handful of problems common to starter motors that generally require replacement. Roller bearings inside the starter housing can fail, allowing the armature to scrape against the inside of the housing. The most common problem occurs when the teeth of either the pinion gear or the flywheel have worn to the point that they can no longer mesh properly, causing an ear-piercing grinding noise. Starter brushes can also fail.
For many cars, you can usually swap out the motor at an auto parts store, but you have no idea where the rebuilt starter was serviced. Most major metropolitan areas--in fact, a lot of small towns--have starter and alternator rebuilders like Auto Electric Warehouse in Merrimack, New Hampshire. They can rebuild your starter on-site, using quality parts and decades of experience.