Recently, I took a number of Trackster starter motors to the local electric motor shop for repair. Of the 6 starters that I delivered, 4 had damaged armatures. The armature is a combination of electric coils and contacts that surround the center spindle or drive shaft of the starter inside the housing. Attached to this shaft outside the housing is the drive pulley/clutch that engages the starter belt. The armature costed about $70.00 per starter to have the coils rewound with new copper wire.
The gentleman at the electric motor shop explained why the armature was bad on so many of the starters. What he explained was that the motor is designed for a specific maximum RPM and if the motor exceeds this speed, centrifugal force throws the windings of the armature out of the spindle and they rub against the stationary outer field windings. This quickly wears through the thin layer of insulation on the copper wire and the starter shorts out and fails.
He continued to explain how this happens with this starter type and as soon as I explain, you'll recognize this common Trackster service scenario. The Trackster starter works on a belt drive system rather than a ring gear system so there is automatically more slippage in the starter design. As we all know, there are times when the starter is cranking the Trackster engine up to speed and the engine will almost start and then the drive pulley disengages and the engine stops turning at that critical moment. Then, the pulley engages again and you start over bringing the engine up to starting speed. If you decide to over tighten the starter to compensate for this slippage of the drive clutch on the starter pullry, it is possible to cause the starter to continue to turn after the engine is running and the key switch has been released. At that moment, the starter is rotating faster than designed. It's a bad thing! Now rev up the engine a bit and the starter is screaming at 10 - 100 times faster than designed. Not to mention... the power loss of spinning this extra appliance.
To properly adjust the starter for long-life operation, it is important to check the starter drive belt for wear and replace (about a 1 hour task) if cracked or worn to thin. Then, adjust the starter so that the outside edge of the belt (where the label and part number is located) rides directly at the highest point of the starter drive pulley at the time the pulley is fully engaged. This allows for the most amount of contact between the drive pulley and the surface of the belt while starting the engine and also allows for the most amount of play or clearance between the belt and drive pulley while the engine is running.
By the way, One of the main reasons for the hard starting scenario listed above can be a bad starter or an old battery. If the starter can't keep the engine turning at starting speed, as soon as the engine fires, it will exceed the speed of the starter motor and the starter drive belt will disengage. However, if everything is working correctly, you can keep starting speed on the engine until it runs.