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CRANKING SYSTEM
The car's cranking system consists of a battery, battery cables, a starter motor, an ignition switch, a starter relay and/or a starter sole-noid, and a neutral safety switch. The starter motor, sometimes re-ferred to as the cranking motor, is a small but very powerful electric motor. It is designed to crank the engine of your car to start it. Here is the way the rest of the system's parts work.
When you turn on the ignition, the battery sends electrical energy to the cranking motor which then converts it to mechanical energy to crank the engine. The relay and/or solenoid, an electromagnetic switch, uses a small amount of battery current, five to ten amperes, in connecting the battery to the cranking motor, and allows a large amount of battery current, 150 to 250 amperes, to activate the crank-ing motor. Because of the very high amperage flow necessary to turn the cranking motor, even the tiniest resistance in the system can be critical. A cranking system that is operating correctly will crank the engine at approximately 180 to 250 revolutions per minute. Any resistance not only inhibits starting efficiency, but also lowers the voltage going to the primary circuit of the ignition system. Think of it in terms of the water main which supplies your neighborhood; any obstruction will lower the flow of water coming into your home.
Resistance is often caused by loose battery cable connections at either the battery, the relay, the starter motor, or the terminals; cor-roded connections at the battery post; poor ground; or a loose or defective cranking motor. There's one other possible cause of re-sistance: heat is created when the cranking motor is operated exces-sively, often because of a poorly-tuned ignition system that causes hard starting. The cranking motor gets hot because of the high am-perage it needs to operate and its inability to dissipate the heat.
The cranking motor on American Motors, Chrysler Motors, and General Motors cars comes equipped with a dual purpose solenoid. It connects the battery to the starter electrically, and engages the starter drive gear to the engine flywheel gear mechanically. On some Ford products, the cranking motor gear is engaged not by a solenoid but by a fork which is operated by an electromagnetic switch located on the starter. This switch engages the starter gear and the flywheel gear and completes the circuit in the cranking motor.
All automatic and some standard transmissions incorporate a neutral safety switch, which prevents the engine from starting when the transmission is in gear. It is usually located on the steering post, close to the floorboard, or on the transmission. Most cars which are equipped with automatic transmissions cannot be push-started, that is, pushed by another car to get the engine going. Because of this situation, it is very important that all of the components of the cranking system be checked and serviced properly. In this chapter, you will learn how to check, charge, and replace the battery; replace the battery cables; and check and replace the cranking motor, the starter relay, and the solenoid.
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