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Bench Testing: Rotor

  1. Place ohmmeter on lowest scale. Connect ohmmeter across rotor slip rings. Resistance should be 3.4-3.8 ohms for 55-amp alternator and 2.8-3.1 ohms for 65 through 90-amp alternators.
  2. If resistance is not as specified, rotor has short circuit and must be replaced. If resistance is infinity (no continuity), rotor has open circuit and must be replaced.
  3. Place ohmmeter on x1000 scale. Connect ohmmeter between either slip ring and rotor core. No continuity should exist. If continuity exists, rotor is grounded and must be replaced.
  4. Clean slip rings using fine sand paper or crocus cloth. Rings which are worn or pitted should be turned on lathe. Minimum slip ring diameter is 1 1/16" (27 mm).
  5. If slip rings are beyond repair, remove rear bearing from slip ring end of rotor. Unsolder wires from slip rings, and bend up ends of rotor winding. Pull off slip rings using puller. Ensure ends of rotor winding are not damaged.
  6. Insert ends of rotor winding into NEW slip ring and press NEW slip ring onto rotor. Ensure slip ring end is 9/64" from end of collar. Solder rotor winding to slip ring terminals. Turn rings on lathe to ensure roundness. Maximum slip ring runout is .0012" (.03 mm). Retest rotor.
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