Starter problems can be caused by worn brushes (carbon pads inside the motor that supply current to the rotating armature), by shorts or opens in the armature or field coils or by worn bushings that increase drag or allow the armature shaft to rub against the pole shoes.
Continuous and prolonged cranking is very hard on a starter motor because it generates excessive heat. If not allowed to cool down every 30 seconds or so for at least a couple of minutes, the starter will be damaged by continuous cranking.
You should have your old starter bench tested to determine if it needs to be replaced. Using a battery and a pair of cables to jump the starter will only tell you if it spins, not how many amps it is drawing or how fast it is cranking. To accurately test a starter, a test stand that can measure amp load, voltage and rpm is required.
A good starter will normally draw 60 to 150 amps with no load on it, and up to 250 amps under load (while cranking the engine). The no load amp draw will vary depending on the type of starter. If the amp draw is too high, the starter needs to be replaced. The same is true if the starter doesn’t achieve the specified rpm.
Excessive starter draw can be caused by high resistance within the starter itself, worn brushes, or grounds or opens in the armature or coil windings. It can also result from increased internal friction due to shaft bushings that bind or an armature that is rubbing against the housing (if the starter is noisy, it’s probably dragging).
Sometimes the starter motor works fine but the drive gear won’t engage the ring gear on the flywheel. If the drive gear mechanism can be replaced separately, there’s no need to replace the entire starter. A bad solenoid can also cause starter problems. The solenoid acts like a relay to route power directly to the starter from the battery. It may be mounted on the starter or located elsewhere in the engine compartment and is usually connected to the positive battery cable. Corrosion, poor ground at the solenoid mount or poor battery cable connections will prevent the solenoid from doing its job.
If the starter tests okay but fails to crank, another possible cause may be a bad ignition switch, neutral safety switch or clutch safety switch. A low battery and/or loose or corroded battery cables can also prevent the starter from cranking the engine.
CHARGING SYSTEM OPERATION
The charging system consists of an alternator (that generates electricity), a voltage regulator (that controls the alternator’s output) and the battery (that stores amps). The charging system’s job is to keep the battery fully charged, and to supply voltage to meet the vehicle’s electrical needs.
Cranking an engine pulls amps out of the battery. These must be replaced, or over time the battery will eventually run down each time the engine is started and driven. As soon as the engine starts, the charging system automatically senses the need for amps and starts recharging the battery. It also produces as many additional amps as are needed to keep the ignition system, fuel injectors and electrical accessories running. As a rule, the charging voltage is about two volts higher than battery voltage.
TYPES OF ALTERNATORS
There are zillions of different OEM part numbers for alternators, so aftermarket suppliers try to consolidate applications as much as possible.
What’s really important is how the alternator is wired (A-circuit, B-circuit or I-circuit), the type of voltage regulation (external regulator, internal regulator or computer-controlled regulation) and the physical hookups (bolt hole locations and indexing, wiring connectors and pulley dimensions).
Alternators with type “A” circuits have an externally grounded field. One brush is connected to positive battery voltage, and the regulator switches between field and negative to control output.
Type “B” circuits have an internally grounded field with one brush connected to battery negative and the regulator switching between field and positive to control output.
A third type of circuitry that is used less often is the “I” type. This configuration has an insulated ground system. In addition to the normal armature terminal that serves as the charge output terminal, it has a second armature terminal normally marked “A2” that serves as the ground return. This type of unit works like an “A” circuit unit and is tested and polarized in the same way, except that the “A2” terminal is used instead of the “A” terminal.
When an A-circuit regulator loses positive voltage, the alternator will overcharge if the field still has power. If the regulator loses its power. If the regulator loses its ground, the system will go dead. With B-circuit systems, just the opposite is true. If a B-circuit regulator loses its ground, the alternator will run wild and overcharge. If it loses positive voltage, the alternator will go dead.
A replacement alternator doesn’t necessarily have to look the same as the original, but it must function the same electrically, have the same pulley dimensions and be a bolt-in replacement. With consolidated applications, it is sometimes necessary to modify or change the wiring connectors as well.