Cummins/Onan MAJ Generator Set

⚠ Disconnect battery ground cable before servicing

Tools: Ohmmeter or continuity tester, Hex-head socket, Socket wrench

1. Disconnect the negative (-) battery cable at the battery terminal.
2. Remove the breaker box cover.
3. Disconnect the breaker box control and magneto leads.
4. Connect an ohmmeter or continuity tester to the hot and ground sides of the breaker points.
5. Remove the spark plugs and turn the rotor through-bolt clockwise until the points begin to open.
6. Adjust the points to open when the flywheel timing mark aligns with the 25 degree mark on the gear case cover.
7. Replace the point box cover, spark plugs, and spark plug leads.
8. Connect the negative (-) battery cable to the negative battery terminal.

⚠ Valves may be damaged by turning them in too far.

Tools: Screwdriver

1. Turn main fuel valve in until engine misses (lean), then out past smooth until uneven (rich); set to mid-point.
2. Hold engine at idle and set low speed adjustment screw until a fast idle of 1200 rpm is obtained.
3. Turn idle adjustment valve in (lean) and out (rich) until engine idles smoothly.
4. Reset low speed adjustment screw so engine idles at 1200 rpm.
5. Release throttle; engine should accelerate without hesitation, readjust main fuel valve if not.

⚠ Forcing mixture adjustment screws tight will damage the needle and seat

Tools: Carburetor adjustment wrench

1. Apply a full load to the engine.
2. Turn in the main fuel adjustment until engine speed drops, then turn out the needle until speed returns to normal.
3. Remove the load from the engine.
4. Turn the idle fuel adjustment out until speed drops slightly, then turn the needle in until speed returns to normal.

1. Install pump with .006-inch (0.15 mm) shims between pump and pad.
2. Loosen delivery valve holder to relieve pressure on spring.
3. Rotate flywheel to about 15 degrees before port closing point.
4. Operate transfer pump hand primer lever and rotate flywheel slowly clockwise until fuel stops coming out of pump outlet.
5. Measure distance from port closing point to PC mark and add shims per table.
6. Install pump.

⚠ Stay clear of rotating components; ensure guards are in place

Tools: Voltmeter, Frequency meter

1. Adjust carburetor fuel mixture screws before governor adjustments.
2. Adjust governor linkage length so the throttle shaft stop almost touches the carburetor stop with engine stopped and tension on the governor spring.
3. With warmed-up unit at no load, adjust the speed adjustment nut to obtain 62 hertz (60 Hz unit) or 52 hertz (50 Hz unit).
4. Check frequency and voltage with load and without load; frequency should not vary more than 5 percent of nominal.
5. Adjust governor sensitivity for closest regulation without hunting; turn sensitivity screw counterclockwise to increase sensitivity.
6. Recheck the speed setting and readjust if necessary.
7. Set the carburetor throttle stop screw as specified under Carburetor Adjustments.

⚠ Injection pump must be timed on the compression stroke, not the exhaust stroke.

Tools: Depth micrometer

1. Install pump tappet in its recess and position flywheel port closing mark at timing pointer on compression stroke.
2. Measure distance from pump mounting pad to tappet center with a depth micrometer.
3. Subtract the depth from the 4.670-inch (42.4 mm) port closing dimension to get shim thickness.
4. Select correct shims and install pump.

Tools: Socket wrench, Feeler gauge

1. Remove all parts necessary to gain access to the valve tappets.
2. Remove the spark plugs to make turning the engine easier.
3. Rotate the crankshaft clockwise until the intake valve opens and closes, then until the flywheel mark aligns with the TC mark on the gear cover.
4. Verify the intake and exhaust valves are closed and there is no pressure on the valve lifters.
5. Measure the valve clearance and turn the adjusting screw as needed to obtain correct clearance.
6. Reinstall all parts, tighten all screws securely, and torque the manifold bolts.

⚠ Do not substitute automotive type electric fuel pumps

Tools: Pressure gauge

1. Remove the fuel line from the pump outlet and install a pressure gauge.
2. Press the START switch and hold it for several seconds until the pressure reading is constant.
3. The pressure reading should be 4-1/2 to 5 psi (31 to 34.5 kPa); if retention is good the pressure should stay constant or drop off very slowly.

Tools: Thermometer, Pan of water

1. Remove thermostat from cylinder head.
2. Heat a pan of water to about 150 F (66 C) and check temperature with a thermometer.
3. Suspend thermostat in water at 150 F; it should start to open.
4. After opening completely (about 165 F [74 C]), remove and allow to cool; it should close within a short time.
5. Replace if it sticks or does not operate properly.
6. Always install a new gasket when replacing the thermostat.

⚠ Do not change the pump mounting shims' total thickness.

Tools: 1/8-inch diameter wire, socket wrench

1. Put No. 1 cylinder on compression stroke.
2. Turn flywheel to port closing mark on front cylinder compression stroke.
3. Remove timing hole screw on pump mounting flange and insert a 1/8-inch diameter wire.
4. Rotate pump face gear until wire slips into place, locking gear.
5. Mount pump on crankcase with shims in place and secure with screws.
6. Remove the 1/8-inch wire.
7. Time pump if not yet timed, using Method 2.
8. Connect flexible fuel inlet line, fuel return line, and each fuel outlet line to proper pump outlet.
9. Connect linkage to governor, run engine and adjust governor maximum stop.

⚠ A dirty mounting surface could permit blow-by, causing nozzle failure and power loss.

1. Install a new heat shield to head gasket in cylinder head recess.
2. Install heat shield, new nozzle gasket and nozzle adapter.
3. Insert nozzle assembly into recess; do not stroke tip against any hard surface.
4. Install nozzle flange and two cap screws, tightening alternately to avoid cocking, to 20-21 ft-lb (27-28 Nm).

⚠ Be sure the slotted opening in the vacuum relief valve is open to atmospheric pressure.

Tools: Pipe straps

1. Locate and hang siphon break vertically within 5 feet (1.5 m) of the exhaust water injection elbow and 12 inches (305 mm) or more above the load waterline.
2. Disconnect exhaust water (raw) discharge hose at the exhaust water injection elbow.
3. Connect exhaust water discharge hose between engine water outlet and siphon break inlet elbow.
4. Connect hose between siphon break outlet elbow and exhaust water injection elbow; tighten all hose clamps.