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Testing & Repair: Rotor

  1. Place ohmmeter on lowest scale. Connect ohmmeter across 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 too low, 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 sandpaper. Rings which are worn or pitted should be turned on lathe. Minimum ring diameter is 1 1/16". If slip rings are beyond repair, replace slip rings as outlined in steps 5) and 6).
  5. 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. Ensure ends of rotor winding are not damaged.
  6. Insert ends of rotor winding into slip ring and press new slip ring onto rotor. Slip ring end must be 9/64" from end of collar. Solder rotor winding to slip ring terminals. Turn rings on lathe and retest rotor. Maximum slip ring run-out is .0012" (.03 mm).
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