Rotor Test: Cs144

Scribe end frames to facilitate reassembly. Remove through bolts and separate end frames.
With ohmmeter set to its lowest range, measure coil resistance between slip rings. See Fig 1. Replace rotor if coil resistance is not 1.7-3.0 ohms at 70°F (21°C).
With ohmmeter set to its highest range, check for grounds between either slip ring and rotor pole piece. See Fig 1. If reading is not close to infinite, replace rotor.

Fig 1: Testing Alternator Rotor (CS144)
Courtesy of GENERAL MOTORS CORP.

NOTE: Manufacturer recommends installing new bearing at slip ring end whenever alternator is reassembled.
To reassemble alternator, reverse disassembly procedure. Retain brushes with brush retaining pin during reassembly. See Fig 2. Remove retaining pin after tightening through bolts.

Fig 2: Removing Brush (CS144)

Courtesy of GENERAL MOTORS CORP.