Cummins/Onan NHEL Generator Set

Tools: vacuum source, drill rod, pliers

1. Apply at least 100 mm mercury vacuum to choke breaker.
2. Insert 8.6 mm drill rod between choke plate and throat.
3. Bend link until choke plate lip touches drill rod.
4. Use two pliers to bend link.

⚠ Forcing mixture screws tight damages needle and seat.

Tools: voltmeter, frequency meter, load bank

1. Stop set and connect voltmeter, frequency meter, and load bank.
2. Start set and apply full load; adjust governor speed nut to 59 (49) ±2 Hz.
3. Remove main adjustment limiter cap; turn main screw inward until voltage or frequency drops.
4. Turn outward until voltage or frequency drops again; locate highest point.
5. Turn main adjustment screw out another 1/4 turn.
6. Remove load and verify frequency within 62-63 Hz (51.5-52.5 Hz).
7. Adjust idle screw for smoothest operation without hunting.
8. Replace limiter caps with lever at mid position.

1. Stop set and allow to cool.
2. Remove plastic choke cover and loosen heating element cover screws.
3. Rotate heating element until choke plate is halfway open.
4. Rotate cover counterclockwise while tapping choke lever until it no longer bounces.
5. Refer to Table 6-2 to determine degrees clockwise from reference.
6. Rotate element cover as specified and tighten screws.
7. Move choke lever to test free operation; install plastic cover.

1. Connect rated load; load watts = volts x amps (1.0 power factor).
2. Check droop from no-load frequency.
3. If droop more than 3 Hz (BGE) or 4 Hz (NHE), turn governor sensitivity screw one turn counterclockwise.
4. Disconnect load and readjust governor speed screw to 62-63 Hz no-load if necessary.
5. If droop less than 2 Hz (BGE) or 3 Hz (NHE), turn sensitivity screw one turn clockwise.
6. Check governor response under 1/4, 1/2 and 3/4 rated loads.

⚠ Disconnect voltage/frequency sensitive devices before adjustments.

1. Set altitude adjust knob (gasoline only) to your altitude.
2. Disconnect all loads and check no-load frequency.
3. Turn governor speed adjusting screw to obtain 62-63 Hz (51.5-52.5 Hz for 50 Hz).
4. Check output voltage; see Generator if not within 10 percent of rated.
5. See Troubleshooting if engine runs roughly.

Tools: frequency meter, voltmeter

1. Set altitude adjust knob to altitude (gasoline only).
2. Disconnect all loads and check zero amps.
3. Adjust governor speed screw for 62-63 Hz no-load (51.5-52.5 Hz).
4. Check output voltage within 10 percent of rated voltage.

⚠ Too much pressure on rod can result in faulty adjustment.

1. Loosen lock nut at ball joint end of governor rod.
2. Unsnap socket from ball.
3. Push governor rod gently towards carburetor (full-throttle).
4. Turn socket to lengthen or shorten rod so ball and socket line up.
5. Snap socket back over ball.
6. Tighten lock nut while holding socket square.
7. Rotate governor arm and check for binding; repeat if necessary.

1. Start genset and warm up ten minutes under 1/2 to 3/4 rated load.
2. Disconnect load and check for zero amps.
3. Pull governor rod so throttle lever tang bears against idle speed stop screw.
4. Adjust screw to obtain 54-56 Hz (44-46 Hz for 50 Hz).
5. On LPG carburetors, stop screw has a locknut.

⚠ LPG is flammable and explosive.

Tools: manometer

1. Close gas shutoff valve(s) at LPG container.
2. Remove 1/8 inch pipe plug from regulator test port.
3. Connect manometer of at least 14 inches range.
4. Open shutoff valve and start genset.
5. Adjust regulator to 11 inches WC (279 mm).
6. Check pressure under full load.

⚠ Adjust valve clearance only when engine is at ambient temperature.

Tools: feeler gauge, socket wrench

1. Remove parts to access valve tappets; remove spark plugs.
2. Rotate crankshaft clockwise until left intake valve opens and closes.
3. Continue until TC mark on flywheel lines up with TC mark on gear cover.
4. Verify left intake and exhaust valves closed and no pressure on lifters.
5. Check clearance with feeler gauge between valve stem and valve tappet.
6. Turn self-locking adjusting screw to obtain correct clearance.
7. Turn engine one revolution and adjust right cylinder.
8. Replace all parts removed and tighten screws securely.

⚠ Most parts cleaning solvents are flammable.

Tools: pressure gauge, compressed air source

1. Connect pressure gauge to regulator test port.
2. Connect compressed air at least 80 psi to inlet.
3. Open air valve; gauge should indicate about 1-1/2 psi constant.
4. Close air valve; pressure should remain constant.
5. Disassemble and clean if either test fails.
6. Replace regulator if it still fails.

⚠ Most parts cleaning solvents are flammable and corrosive.

Tools: pressure gauge, compressed air source

1. Connect pressure gauge to test port on back of regulator.
2. Connect compressed air at least 80 psi (550 kPa) to inlet opening.
3. If primary valve sound, gauge reads approximately 1-1/2 psi (10.3 kPa) and holds steady.
4. Close air valve and observe gauge; pressure drop indicates secondary valve seat leaking.
5. Disassemble and clean regulator if it fails either test; replace if still fails.