Bench Testing: Rotor

Check the face of the slip rings for contamination and roughness. See Fig 1 . If found to be scored, dress with a fine sandpaper (#500 - 600). If found to be contaminated, clean with a cloth saturated with alcohol.
Measure the outside diameter of the slip rings. See GENERATOR SPECIFICATIONS .
Check resistance between slip rings, and replace if there is no continuity. See Fig 2 .
Check for continuity between slip ring and rotor core. If there is a continuity, replace the rotor assembly. See Fig 2 .

Fig 1: Identifying Rotor Components

Courtesy of AMERICAN HONDA MOTOR CO., INC.

Fig 2: Checking Rotor For Open Or Grounded Circuits

Courtesy of ISUZU MOTOR CO.