Cummins/Onan — Testing Armature and Field Windings
Testing & diagnosis · generator windings
From a Cummins/Onan service manual covering: 4CCK, 5CCK, 5CCK-150R, 5CCK-3CR. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4CCK, Cummins/Onan 5CCK, Cummins/Onan CCK engine
Before you start
- Replace a grounded, open-circuited, or short-circuited armature with a new one
Procedure
- Lift or remove all brushes so none contact commutator or collector rings.
- For ground test, use a continuity test lamp set: one prod on commutator, other on bare armature shaft; lamp must not glow.
- Test ac winding between collector rings; lamp should glow.
- For dc open circuit test, place armature in a growler; pass a smooth steel strip across commutator segments.
- A spark at each adjacent segment pair indicates no open circuit.
- For short circuit test, hold a steel strip about 1/2 in. above the armature laminations in a growler; magnetic attraction indicates a short.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Maximum 0.002 in. run-out of collector ring compared to generator bearing
Full service-parts list: Cummins/Onan 4CCK →, Cummins/Onan 5CCK →
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.