Alternator: Testing and Inspection

INSPECTION

1. DIODE

CAUTION: Never use a megger tester (measuring use for high voltage) or any other similar measure for this test; otherwise, the diodes may be damaged.




1. Checking positive diode:
Check for continuity between the diode lead and the positive side heat sink. The positive diode is in good condition if continuity exists only in the direction from the diode lead to the heat sink.




2. Checking negative diode:
Check for continuity between the negative side heat sink and diode lead. The negative diode is in good condition if continuity exists only in the direction from the heat sink to the diode lead.

2. ROTOR

1. Slip ring surface:
Inspect the slip rings for contamination or any roughness of the sliding surface. Repair the slip ring surface using a lathe or sand paper.

2. Slip ring outer diameter:
Measure the slip ring outer diameter. If the slip ring is worn replace the rotor assembly.

Slip ring outer diameter:

Standard
22.7 mm (0.894 in)

Limit
22.1 mm (0.870 in)




3. Continuity test:
Check the resistance between slip rings using a circuit tester.

If the resistance is not within specification, replace the rotor assembly.




4. Insulation test:
Check the continuity between slip ring and rotor core or shaft. If the resistance value is below 1 Ohm, the rotor coil is grounded, and so replace the rotor assembly.




5. Ball bearing (rear side):

1. Check the rear ball bearing. Replace if it is noisy or if the rotor does not turn smoothly.
2. The rear bearing can be removed by using a common bearing puller.

3. STATOR




1. Continuity test:
Inspect the stator coil for continuity between each end of the lead wires. If the resistance value is above 1 M Ohm between individual lead wires, the lead wire is broken, and so replace the stator assembly.




2. Insulation test:
Inspect the stator coil for continuity between stator coil and each end of the lead wire. If the resistance value is below 1 Ohm, the stator coil is grounded, and so replace the stator assembly.

4. BRUSH




1. Measure the length of each brush. If wear exceeds the service limit, replace the brush. Each brush has the service limit mark (A) on it.




2. Checking brush spring for proper pressure:
Using a spring pressure indicator, push the brush into the brush holder until its tip protrudes 2 mm (0.08 in). Then measure the pressure of the brush spring. If the pressure is less than 2.648 N (270 g, 9.52 oz), replace the brush spring with a new one. The new spring must have a pressure of 4.609 to 5.786 N (470 to 590 g, 16.58 to 20.81 oz).

5. BEARING (FRONT SIDE)
1. Check the front ball bearing. If resistance is felt while rotating, or if abnormal noise is heard, replace the ball bearing.




2. Replacing front bearing:
1. Remove the front bearing retainer.
2. Closely install a fit tool on the bearing inner race. Press the bearing down out of front bracket with a hand press or vise. A socket wrench can serve as the tool.
3. Set a new bearing and closely install a fit tool on the bearing outer race. Press the bearing down into place with a hand press or vise. A socket wrench can serve as the tool.




4. Install the front bearing retainer.