Cummins/Onan L Series Diesel Engine

Tools: Voltmeter

1. With starter motor operating, check voltage drop from battery negative post (not cable clamp) to cylinder block.
2. Check voltage drop from battery positive post to battery terminal stud on solenoid.
3. Normally each should be less than 0.3 volt; slightly higher may result with extra long battery cables.
4. Thoroughly clean all connections in any part of the circuit showing excessive voltage drop.

⚠ Voltage regulator VR1 is potted and not repairable.

Tools: Voltmeter

1. With engine running, connect a voltmeter across the battery terminals.
2. Meter should read 13.5 to 15 volts.
3. Charge rate/voltage is determined by battery state-of-charge and circuit resistance.
4. Power source is winding CW1 on main stator; if charging voltage is incorrect or missing, check wiring and circuit components.
5. Improper operation may be caused by poor terminal connections, broken wires, or a defective battery.

⚠ Ignition of fuel can cause serious personal injury or death by fire or explosion; no flame, cigarette or other igniter near the fuel system.

1. Fuel solenoid is located in the governor control cover on top of the fuel injection pump.
2. Listen for solenoid actuation when B+ is applied (start switch in Start position).
3. If there is no click when B+ is applied and again when removed, the fuel solenoid must be replaced.
4. See Fuel System section of L Series Diesel Engine Service Manual (934-0750) for replacement procedure.

Tools: Voltmeter, Voltage source

1. Determine coil and contact terminals from the schematic diagram; numbers/letters are stamped on the relay.
2. Apply rated voltage across the relay coil terminals; relay should activate if coil is okay.
3. Connect voltage source to one side of relay contacts; connect voltmeter to other side and to voltage source.
4. If voltage appears when relay energizes, contact is okay.
5. Voltage reading appears in reverse order when checking normally closed (NC) contacts.

Tools: 12-volt battery, Ohmmeter, Voltmeter

1. Apply 12-volt battery positive (+) to the K11 coil terminal S.
2. Connect a wire from the battery negative (-) to coil terminal 1; the solenoid should activate.
3. If contacts are good, zero resistance should be read across the large terminals when coil is activated.
4. Voltage drop across the contacts should never exceed one volt in circuit application.

⚠ Disconnect negative battery cable first.

Tools: Ohmmeter

1. Disconnect the starting battery cables, the negative (-) cable first.
2. Connect an ohmmeter across the switch terminals.
3. Open and close the switch while observing the ohmmeter; note operation of normally open (NO) and normally closed (NC) contacts.
4. Replace the switch if defective.

⚠ Contact with rotating parts can cause severe personal injury or death; keep hands and clothing away.

⚠ Ignition of explosive battery gases can cause severe personal injury; no flame, spark, cigarette or ignition source near battery.

Tools: Ohmmeter

1. Disconnect all leads from assembly to be tested.
2. Connect one test lead to F1+ stud and the other to CR1, CR2 and CR3 in turn; record resistance of each rectifier.
3. Connect one lead to F2- stud and the other to CR4, CR5 and CR6 in turn; record resistance of each rectifier.
4. Reverse ohmmeter leads from steps 2 and 3 and record resistance of each rectifier.
5. Resistance readings should be high in one test and low in the other; if high or low in both tests, assembly is defective.
6. Replace defective rectifier assembly with new identical part.

Tools: Ohmmeter

1. Inspect all wires for breaks, loose connections and reversed connections; refer to applicable wiring diagram.
2. Remove wires from terminals at each end and using an ohmmeter check each wire end to end for continuity or opens.
3. Using an ohmmeter, check each wire against each of the other wires and to ground for shorts or insulation breaks.
4. Reconnect or replace wires following the applicable wiring diagram.

⚠ Ignition of explosive battery gases can cause severe personal injury; no flame, spark, cigarette or other ignition source near the battery.

Tools: Hydrometer

1. Check charge condition of battery with a hydrometer.
2. Electrolyte specific gravity should be about 1.260 for a fully charged battery at 80°F (27°C).
3. If not, add distilled water to keep electrolyte at proper level and recharge battery.
4. If battery will not recharge, replace it.
5. If battery state-of-charge is not maintained, charge rate may be too low; see Checkout [C].

⚠ Incorrect flashing procedure can damage the generator or regulator components.

Tools: 12-volt storage battery, 10-amp fuse, Momentary-on switch, Diode

1. Assemble a 12-volt storage battery, 10-amp fuse, momentary-on switch, and diode as shown in Figure 4-2.
2. Remove generator end bell cover.
3. Connect positive (+) battery lead to F1+ terminal and negative (-) battery lead to F1- terminal on end bell terminal board.
4. Start generator set and operate at normal speed.
5. Close momentary switch just long enough for output voltage to build up, but no longer than 5 seconds.

⚠ Accidental starting can cause severe personal injury or death; disconnect negative battery cable.

⚠ Dropping the stator assembly can cause severe personal injury or death; ensure lifting device is secure and strong.

⚠ The end bearing will be damaged if pulled on the outer race. If reused, pull on the inner race.

Tools: Hoist and lifting device, Gear puller, Wood blocks

1. Disconnect the negative (-) battery cable to prevent accidental starting.
2. Remove cover from AC control box. Disconnect main stator leads T1-T4 and voltage leads 1 and 2.
3. Remove end bell cover. Disconnect field leads F1 and F2 from terminal board and leads from battery charge regulator.
4. Remove regulator from end bell. Remove load wires and flexible conduit from AC control box. Unplug connectors J1-J3.
5. Remove capscrews securing mounting saddle to stator; control boxes and saddle remove as an assembly.
6. Pull stator leads through opening in bottom of AC control box while lifting assembly free.
7. Remove stud nuts and slide end bell/exciter stator assembly off main stator; pry or jar loose if necessary.
8. Use hoist and safe lifting device to support stator assembly.
9. Remove stator assembly without touching or dragging it on rotor; place on side and block to prevent rolling.
10. Remove two-section air baffle from generator adapter.
11. Support rotor with hoist and sling; remove capscrews attaching drive disk to engine flywheel.
12. Remove rotor assembly and place on wood blocks horizontally; drive disk and fan must not rest on anything.
13. Remove bolts holding drive disk and fan to rotor shaft.
14. Use gear puller to remove end bearing from rotor shaft, pulling on the inner race only.
15. Clamp rotor in fixed position, remove exciter rotor lock nut, remove generator field leads and slide exciter off rotor shaft.

⚠ Assemble drive disk with chamfer on flywheel side.

⚠ Disconnect negative battery cable before service.

Tools: Hoist and sling, Lead hammer, Torque wrench

1. Slide exciter rotor over generator shaft and woodruff key; install exciter nut and apply torque values shown in Figure 2-9.
2. Connect generator field leads to F1+ and F2- terminals on exciter assembly; torque to values shown.
3. Press end bearing onto rotor shaft.
4. Assemble rotor fan and drive disk to engine flywheel using hoist and sling; chamfer must be on flywheel side.
5. Apply torque values shown in Figure 2-9. Install air baffle.
6. Using hoist and safe lifting device, carefully move stator into position over rotor with leads exiting in top position.
7. Install end bell stud bolts through stator and into generator adapter.
8. Apply thin film of Molykote grease to mating surfaces of end bearing and end bearing hole.
9. Install end bell assembly on stator with generator lead opening at top position.
10. Replace stud nuts and torque to 20 ft lbs (27 Nm); install battery charge regulator bracket in upright position with ground lead terminal under mounting screw.
11. Using a lead hammer, tap end bell at horizontal and vertical plane to relieve stress; retorque end bell stud nuts.
12. Route generator leads through opening in AC control box and secure saddle to generator.
13. Connect control leads and verify all connections are correct and secure.
14. Connect field leads F1 and F2 to terminal board and leads to battery charge regulator; install end bell cover.
15. Connect load wires to correct terminals, connect negative (-) battery cable and test generator operation.