Cummins/Onan — Carbon Brush / Slip Ring Inspection
Testing & diagnosis · Generator brush holder
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Procedure
- Remove carbon brushes from brush holder.
- Check brush for length and wear; replace if length is less than 5 mm (0.20 in).
- Connect Blue wire lead to positive (+) side of brush holder.
- Avoid damaging brushes when removing and installing brush holder.
- Inspect slip rings for dust, rust or damage; wipe with clean lint-free cloth.
- If rusted or damaged, remove rotor and rub with fine emery cloth.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Brush length limit: 5 mm (0.20 in)
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.