Provide grip over armature shaft
Avoid the side way movement of armature shaft
Prevent pinion striking fly wheel
Resist wear on the fly wheel
Faulty regulator
Loose mountings
Wornout bearing
Loose drive pully
Open rectifier circuit
Open field current
Voltage regulator setting too low
Voltage regulator setting too high
Charges at high rate
Low voltage output from alternator
No change when engine running
Alternator noisy
Drive belt loose
Shorted rectifier
Sticky regulator
Brushes not seating properly