The Harley-Davidson Electric Starter Motor

You would be hard pressed to find a Harley Davidson rider who hasn't had the aggravation of dealing with electrical-starter issues at one time or another. Ever since 1964 when Harley introduced its first electric starter on the Harley-Davidson Servi-Car, (in 1965 the venerable thumb-starter appeared on the Electra-Glide, with the XLH Sportster the recipient in 1967) electric start has been both a blessing and a curse – at least for some of us. With today's large-displacement, high-compression engines, starting systems must work hard under a variety of demanding conditions. Add to that the amount of time many motorcycle sit idle in between rides, and it's no surprise that scores of riders find themselves staring at starting problems.

Harley-Davidson's starting systems is made up of various components including the starter motor, battery, battery cables, and starter relay. The starter motor is considered the heart of the system, and it includes the 12-volt DC motor, a gear reduction system, a clutch assembly, a solenoid/plunger assembly, and internal heavy-duty copper contacts. Operation of the motor is simple although multiple steps take place in rapid succession once you let you right thumb begin the starting sequence.
When you thumb the starter button, the starter relay (located under the seat or behind a side cover) pulls in a set of contacts allowing electricity to flow to a coil in the solenoid section of the starter. The coil creates a magnetic field pulling in the plunger. AS the plunger reaches the end of its travel, it makes contact with a pair of large copper contacts that allow voltage to flow from the positive battery cable, through the field windings in the starter's yolk assembly and armature, thus spinning the motor's shaft.

With the shaft spinning, a small gear on the armature turns an idler gear, which in turn rotates the starter clutch. The spinning of these gears trades high RPM for the torque needed to turn the engine's crankshaft over. At this point the output shaft and pinion gear have been pushed toward the primary by the plunger to engage with the ring gear attached to the clutch assembly – spinning the primary drive and engine's crankshaft fast enough to synchronize, allowing the engine it-self to start. All in all, a rather straightforward process when everything works as intended.

Since there's only so much preventative maintenance you can do the starter itself, it's important that you allow the entire starting system to perform at its maximum potential at all times. If all the system's components aren't functioning properly, you eventually risk some sort of failure.
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