Cummins/Onan — Permanent Magnet Exciter Removal
Repair & overhaul
From a Cummins/Onan service manual covering: 4BT3.9, 4BT3.9-GC1, 4BT3.9-GC2, 6BT5.9, 6BT5.9-GC1, 6BT5.9-GC2, 6CT8.3, 6CT8.3-GS/GC1, 6CTA8.3, 6CTA8.3-GS/GC1, 6CTA8.3-GS/GC2. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4BT3.9, Cummins/Onan 6BT5.9, Cummins/Onan 6CTA8.3, Cummins/Onan 4BT3.9 engine, Cummins/Onan 6BT5.9 engine, Cummins/Onan 6CT8.3 engine, Cummins/Onan 6CTA8.3 engine
Before you start
- The rotor assembly should under no circumstances be dismantled, or magnetic properties will be destroyed.
- The highly magnetic rotor will attract the stator core; avoid contact that may damage windings.
Procedure
- Disconnect negative (-) battery cable to prevent accidental starting.
- Remove endbell cover and conduit box access covers.
- Disconnect and withdraw leads P2, P3, P4 from auxiliary terminal block.
- Remove bolts and clamps retaining exciter stator to endbracket.
- Guide stator assembly from endbracket, avoiding contact with magnetic rotor.
- Remove through-bolt and firmly pull complete rotor assembly from location.
- Locate dowel pin on rotor shaft; remove and retain for reassembly.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
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.