How Does a Starter and Solenoid Work?

Introduction:

An engine starter is designed to utilize a 12 volt, high amperage electrical system made to turn an engine over for starting purposes via a flywheel. Basically a starter is an electric motor with a small pinion gear and bendix assembly. This starter bendix drive is designed to extend and mesh with the flywheel teeth when the ignition key is turned to the "crank" position and then retract when the ignition key is released after the engine has started. A starter motor is constructed with a main outer housing that contains the armature magnets, the armature contains the starter windings, a brush set that is used to contact the armature to transfer the electrical energy. The starter bendix is directly connected to the starter pinion gear. A starter solenoid acts as the main power switch to begin the starter operation. Because the starter motor draws such high amperage a conventional switch would short circuit very quickly. Most starter solenoids are located on the starter motor itself. Some Ford models have located the starter solenoid on the inner fender panel near the battery. The electrical system that controls the starter motor is comprised of an ignition switch, neutral safety switch (automatic transmissions only) a clutch engagement switch (manual transmissions only) a battery, battery cables, anti theft system and the starter itself.

Typical Starter Motor

Most starter motors are mounted underneath the car near the flywheel on either the left or right side. The flywheel is located between the engine and transmission. Some models have located the starter under the intake manifold, which makes replacement difficult. When the ignition key is turned to the "engine crank" position a 12 volt low amperage electrical signal is sent to the anti-theft system which in turn can monitor the gear selection or clutch safety switch position. Only then will the signal continue to the starter solenoid that activates the high amperage side of the electrical system to engage the starter motor.

Once the starter motor has been engaged the starter bendix senses the armature momentum and is forced to extend into the flywheel. Once the engine has started and the ignition key released the bendix loses momentum and the bendix is forced to return to idle position. If the flywheel is worn it can cause a grinding noise when the starter bendix/pinion gear is engaged. The objective of the starter motor is to rotate the engine between 85 and 150 rpm's necessary for engine ignition process. A starter will typical last between 60,000 and 100,000 miles and is a normal replacement item.

Replacement Guide

Tools needed:

Set of sockets and socket wrench with extensions

Phillips and standard screw drivers

Pliers

Wrench set

Replacement Procedure:

Start with engine cold

Remove the negative battery cable at the battery

Remove all electrical wires that lead to the wiring harness and main battery cable connections. (note: sometimes this step is easier after the starter motor has been removed)

Remove all accessories (if any) to access starter motor mounting bolts, next remove starter motor mounting bolts, remove the starter.

Clean starter mounting surfaces thoroughly

Install new starter and tighten evenly

Reconnect wiring and cable

Reconnect the negative battery cable (note: if major spark are present when the battery is re-connected the starter battery connection needs to be inspected)

Recheck starter operation (note: if the starter motor operation is exce

ssively noisy the starter motor may need to be repositioned using shims)