Cummins/Onan — Test Rotor Continuity
Testing & diagnosis
From a Cummins/Onan service manual covering: 02SX1N1A, 04SX1N, 04SX1N1A, 04SX1N1B, 04SX1N2B, 04SX1N3B, 04SX1N4B, 06SX1N, 06SX1N1A, 06SX1N1B, 06SX1N2B, 06SX1N3B…. Check it applies to your exact model before use.
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Procedure
- Remove brushes so none touch collector rings.
- Using ohmmeter, test for grounding between each slip ring and rotor shaft.
- Test for short or open in rotor winding by measuring resistance.
- It should measure between 3.5 and 4.8 ohms for JB and between 2 and 3 ohms for JC at 70°F.
- If accurate ohmmeter not available, check for open circuit or grounding with AC test lamp.
- Replace rotor if grounded, open circuit, or shorted.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 3.5-4.8 ohms JB at 70°F
- 2-3 ohms JC at 70°F
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.