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Cummins/Onan — Generator Disassembly

Repair & overhaul · Generator (YD series)

From a Cummins/Onan service manual covering: MDL3, MDL4, MDL6. Check it applies to your exact model before use.

Applies to: Cummins/Onan MDL3, Cummins/Onan MDL4, Cummins/Onan MDL6

Before you start

  • Disconnect the battery cables when repairs are made to the engine, controls, or generator.
  • Generator sets are heavy and can result in severe personal injury or death if dropped during removal. Use adequate lifting devices.

Procedure

  1. Disconnect the battery cables to prevent accidental starting.
  2. Remove control box cover and disconnect all stator leads; mark leads if not clearly identified.
  3. Remove end bell cover; remove field leads F1 and F2; disconnect overspeed switch and battery charging leads.
  4. Remove load wires and flexible conduit from control box.
  5. Remove capscrews securing control box mounting saddle to stator; remove control box and saddle as an assembly.
  6. Pull stator leads through opening in bottom of control box; do not disconnect engine DC control wires.
  7. Set control box and saddle on top of engine.
  8. Remove overspeed switch/bracket assembly from end bell.
  9. Remove end bell stud nuts and slide off end bell and exciter stator.
  10. Support stator assembly with hoist and safe lifting device; remove stator and place on its side horizontally.
  11. Remove the two-section air baffle from the generator adapter.
  12. Support rotor with hoist and sling; remove capscrews attaching drive disk to engine flywheel.
  13. Remove rotor assembly and place on wood blocks in horizontal position.
  14. Remove bolts holding drive disk and fan to rotor shaft; use gear puller to remove end bearing.
  15. Clamp rotor, remove exciter rotor lock nut, remove generator field leads and slide exciter off rotor shaft.

Tools required

  • Hoist Amazon
  • Safe lifting device (stator handling tongs, nylon lifting strap or chain and lift hooks) Amazon
  • Gear puller Amazon
  • Sling Amazon

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • Drive disk to flywheel torque 39 ft lbs (52 N·m)
  • Rotor assembly torque 176-203 Amazon eBay N·m (Figure 2-9)
  • F1+/F2- and CR1 through CR6 nuts 23-26 inch lbs (2.6-2.9 N·m)

Full service-parts list: Cummins/Onan MDL3 →, Cummins/Onan MDL4 →, Cummins/Onan MDL6 →

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.

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