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Cummins/Onan NH Engine

The Cummins/Onan NH is a 2-cylinder engine rated at 3600 rpm, producing up to 5.5 kW. It powers generator sets from Cummins/Onan, including the 6.5 NH. It holds 3.3 L (0.9 gal) of oil.

Also known as: Onan NH

Cylinders

3600 rpm

Rated speed

5 kW

Gross power

3.3 L

Oil capacity

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Procedures Wiring

Engine specifications

Oil capacity	3.3 L
Cylinders	2
Rated speed	3600 rpm
Gross power	5 kW

Generator sets powered by this engine

Cummins/Onan 6.5 NH

How to read your Cummins/Onan engine serial & model number →

Troubleshooting

Fault codes

Code	Meaning
loss	Loss of coolant

Symptoms & remedies

Symptom	Cause	Remedy
Disconnecting Set from RV Systems		1. First disconnect the negative (-) battery cable from the baitery and then disconnect the battery cables from the genset. 2. Disconnect the remote control wiring harness connector at the genset. 3. Disconnect the generator output wiring and conduit from the power distribution panel or box on the vehicle. Tag all wires to make reconnections easier. 4. Disconnect the exhaust tailpipe from the outlet of the muffler and then remove the muffler. See EXHAUST SYSTEM under Engine Subsystems. 5. Disconnect the fuel line from the genset. Follow the applicable instructions depending on the fuel.
Engine Misfires	Faulty ignition due to: a. worn or fouled spark plugs. b. worn breaker points. c. incorrect ignition timing. d. faulty ignition coil, e. faulty plug wires. f. faulty condenser. g. faulty ignition module (electronic ignition); Lean fuel mixture due to: a. incorrectly adjusted fuel mixture screws. *b. incorrect float level. c. dirt in carburetor. d. vacuum leak.; Contaminated fuel; Carburetor icing Gasoline sets only.	A. Replace spark plugs. b. Replace breaker points. c. Set breaker point gap. d. Test coil and replace if necessary. e. Test spark plug wires and f. Replace condenser. g. See Testing Ignition Module.; 2a. Adjust carburetor main and idle adjustment screws. b. Adjust carburetor float level. c. Disassemble carburetor and clean all internal passages. d. Locate leak and correct as required.; 3. Drain fuel tank and refill with fresh fuel. 4. In cold weather, place air preheater in winter position.
Engine Backfires	Faulty ignition due to: a. worn or fouled spark plugs. b. worn breaker points. c. incorrect ignition timing. d. faulty ignition coil, e. faulty plug wires. f. faulty condenser. g. faulty ignition module (electronic ignition)	A. Replace spark plugs. b. Replace breaker points. c. Set breaker point gap. d. Test coil and replace if necessary. e. Test spark plug wires and f. Replace condenser. g. See Testing Ignition Module.
Engine Lacks Power	Faulty ignition due to: a. incorrect ignition timing. b. incorrect spark plug gap. c. faulty condenser.	A. Adjust breaker point gap. b. Reset spark plug gap. c. Replace condenser.
Engine Overheats	Mechanical damage to engine *Gasoline sets only.	See Engine Block Assembly section.
Engine Hunts or Surges	1. Sticking or binding governor linkage. 2. Incorrect governor adjustment 3. Faulty governor spring. 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, or c. dirt in carburetor. 5. Governor mechanism worn excessively. *6. Carburetor icing.	1. Clean and lubricate governor linkage. 2. Adjust governor speed and sensitivity. 3. Replace governor spring. 4a. Adjust carburetor main and idle adjustment screws. 4c. Disassemble carburetor and clean all internal passages.
High Oil Consumption	1. Oil viscosity too light or oil is diluted. 2. Crankcase breather valve is dirty or defective. 3. Oil leaks.	1. Drain oil and refill with correct viscosity oil. 2. Clean crankcase breather and replace if defective. 3. Locate source of leak and repair as required.
Low Oil Pressure	1. Oil viscosity too light or oil is diluted. 2. Low oil level. 3. Low oil pressure switch defective. 4. Faulty oil bypass valve.	1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section.).
Black Exhaust Smoke	Lean fuel mixture due to: a. incorrectly adjusted fuel mixture screws. b. incorrect float level. c. dirt in carburetor. d. vacuum leak.	3a. Adjust carburetor main and idle adjustment screws. 1b. Adjust carburetor float level. 1c. Disassemble carburetor and clean all internal passages. 1 Replace fuel filter. 4d. Repair vacuum leak.
White or Blue Exhaust Smoke	Rich fuel mixture due to: a. incorrect float level b. faulty carburetor float.	1a. Adjust carburetor float level. 1b. Replace faulty carburetor float.
Engine surges	1. Sticking or binding (mechanical) governor linkage. 2. Incorrect (mechanical) governor adjustment. 3. Faulty (mechanical) governor spring. 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws.1 b. incorrect float level.1. 2 c. dirt in carburetor d. ignition misfires 5. Intermittent electrical connections. 6. Governor mechanism worn excessively. 7. Fuel supply problem caused by: a. Faulty fuel pump.2 b. Contaminated fuel supply.2 c. Vapor locking.2 d. Plugged fuel filter	1. Clean governor linkage (remove dirt or ice buildup). Check that linkage does not touch other parts. 2. Adjust governor speed and sensitivity. 3. Replace governor spring. 4a. Adjust carburetor main and idle adjustment screws.1 4b. Adjust carburetor float level.1 4c. Disassemble carburetor and clean all internal passages.1 4d. Check connections, see Ignition section. 5. Check battery and ignition connections. 6. See Engine Block Assembly section.. 7a. Check fuel pump and replace if defective. 7b. Drain and refill fuel supply 7c. Check for cause of overheating 7d. Replace fuel filter.
Make sure there is ample fresh air when operating the genset in a confined area.		Ensure adequate ventilation when operating the genset in a confined space.
Overheats	Restricted airflow due to: a.debris blocking air inlet or outlet.	Clear away debris. Do not use genset compartment for storage.
Lean fuel mixture	A.incorrectly adjusted fuel mixture screws.	Adjust carburetor main and idle adjustment screws.1
Contaminated fuel supply	2.Contaminated fuel.2	Drain and replace fuel.
Governor mechanism worn excessively	6.Governor mechanism worn excessively.	See Engine Block Assembly section.
Sticking or binding (mechanical) governor linkage	1.Clean governor linkage (remove dirt or ice buildup). Check that linkage does not touch other parts.
Incorrect (mechanical) governor adjustment	2.Incorrect (mechanical) governor adjustment.	Adjust governor speed and sensitivity.
Faulty (mechanical) governor spring	3.Faulty (mechanical) governor spring.	Replace governor spring.
Incorrect fuel mixture	4a. Adjust carburetor main and idle adjustment screws.	Adjust carburetor main and idle adjustment screws.1
Intermittent electrical connections	5.Intermittent electrical connections.	Check battery and ignition connections.
Fuel supply problem caused by: a.Faulty fuel pump.		Check fuel pump and replace if defective.
Fuel supply problem caused by: b.Contaminated fuel supply.		Drain and refill fuel supply
Fuel supply problem caused by: c. Vapor locking.		Check for cause of overheating
Fuel supply problem caused by: d.Plugged fuel filter.		Replace fuel filter.
Carburetor icing	8.Carburetor icing.2	In cold weather, place air preheater in winter position.
Faulty ignition due to: a. worn or fouled spark plugs.	Misfires	Replace spark plugs.
Faulty ignition due to: b. faulty ignition coil.	Misfires	Test coil and replace if necessary.
Faulty ignition due to: c. faulty plug wires.	Misfires	Test spark plug wires and replace if faulty.
Lean fuel mixture due to: a. incorrectly adjusted main and idle adjustment screws.		Adjust carburetor main and idle adjustment screws.
Lean fuel mixture due to: b. incorrect float level.		Adjust carburetor float level.
Lean fuel mixture due to: c. dirt in carburetor.		Disassemble carburetor and clean all internal passages. Replace fuel filter.
Lean fuel mixture due to: d. vacuum leak.		Locate leak and correct as required.
Lean fuel mixture due to: e. altitude setting.		Reset altitude adjust knob on carburetor.
Contaminated fuel.		Drain fuel tank and refill with fresh fuel.
Carburetor icing.		Place air preheater in winter position.
Faulty ignition due to incorrect spark plug gap.		Reset spark plug gap.
Dirty air cleaner.		Replace air cleaner.
Restricted fuel flow due to: a. Plugged fuel filter.		Replace fuel filter.
Dizziness		IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired.
Muscular Twitching		IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired.
Vomiting		IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired.
Weakness and Sleepiness		IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired.
Inability to Think Coherently		IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired.
FAILS TO CRANK	1. Low battery 2. Bad battery connection 3. Blown fuse.
CRANKS SLOWLY	1. Low battery.	1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections.
CRANKS BUT WON'T START	Faulty Fuel Solenoid or Plugged Fuel Filter, Faulty Ignition	Fuel solenoid must open during cranking and running. Check by cranking set with spark plugs disconnected. Push priming button on regulator and listen for fuel flow and propane odor. If no flow or odor, check and replace fuel filter or fuel solenoid valve., Check to see if points open and close during cranking. If they do not open and close, adjust and set points. Plug and plug wires must be in good condition. Voltage at ignition coil negative terminal (-) must alternate from +12 volts to zero as points open and close during engine cranking., Check voltage from relay terminal '4' to ground while cranking unit. Battery voltage should appear at this terminal. If not check
CRANKS BUT WON’T START	1. Fuel below genset pick-up level 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plugs. 4. Blown fuel pump/in tank.	1. Add fuel. 2. Fully open fuel supply valve. 3. Remove spark plugs and clean. 4. Replace fuse with same type and rating. If problem persists, see Onan service center.
EXHAUSTING BLACK SMOKE	1. Rich fuel mixture. 2. Dirty air filter. 3. Choke stuck.	1. Turn main fuel adjustment in 1/8 turn (location of adjustment is shown in Figure 3-1). 2. Replace air filter. 3. Contact an Onan service center.
UNIT RUNS THEN STOPS	1. Out of fuel. 2. Low oil level. 3. Excess oil.	1. Refill fuel tank. 2. Add oil if necessary. 3. Reduce engine oil level.
UNIT RUNS BUT SURGES	1. Loose or worn spark plug leads at spark plugs and ignition coil. 2. Ignition coil, wiring, or control components defective. 3. Faulty spark plugs. 4. Governor out of adjustment.	1. Check security of spark plug leads at spark plugs and ignition coil. Replace leads if worn. 2. Contact an Onan representative. 3. Remove and clean or replace faulty spark plugs. 4. Contact an Onan service center.
Low Bat LED (red) MAY flash ON		If it stays on during operation, see BATTERY CARE under Periodic Maintenance.
Engine does not crank or start after several tries or stops running.		See Troubleshooting if the engine does not crank or start after several tries or stops running.
The engine fails to crank at the remote START switch.		A. Turn the enable switch (if so equipped) to the enable position. b. Try starting at the genset rather than at the remote control. c. Push the genset control panel switch to RESET and then to START.
The engine fails to crank at the genset START switch and Start Sol (Fig. 3) does not light.		A. Turn the enable switch (if so equipped) to the enable position. b. Push the genset control panel switch to RESET and then to START. c. Replace fuse F1 on the side of the control box if it has blown. d. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. e. Recharge the battery. Refer to the battery manufacturer’s recommendations.
The engine fails to crank at the genset START switch but Start Sol (Fig. 3) does light.		A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations.
The engine cranks slowly.		A. Disconnect large electrical and mechanical loads. b. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. c. Recharge the battery. Refer to the battery manufacturer’s recommendations. d. Change the engine oil to oil having the proper viscosity for the ambient temperature. See Table 1 on Page 3.
The engine cranks but fails to start. Fuel Pump, AVR Field and Ignition (Fig. 3) do light.		A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Service the air cleaner. e. Secure the spark plug leads on the spark plugs. f. Replace the spark plugs.
The engine cranks but fails to start. Fuel Pump, AVR Field or Ignition (Fig. 3) does not light.		Contact an authorized Onan dealer.
The engine runs and then stops or surges.		A. Check the fuel tank and fill if necessary. b. Check the engine oil level and add oil as necessary. Drain excess oil if the level is above the dipstick Full mark. c. Check and reset the carburetor preheater lever and altitude adjust knob (gasoline models only). See Varying Weather and Altitude. d. Secure the spark plug leads on the spark plugs. e. Replace the spark plugs.
The genset keeps stalling or the circuit breaker keeps tripping.		A. Try running with fewer appliances connected. See Powering Equipment. b. Check the fuel tank (LPG, vapor-withdrawal models) and fill as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand.
There is no electrical power even though the genset runs and Gen AC (Fig. 3) lights.		A. Reset tripped circuit breakers. See Powering Equipment. b. Unless there is an automatic power transfer switch, plug the vehicle power cord into the genset power output receptacle (if so equipped) or turn the vehicle power selector switch to its genset position (if so equipped).
Low Bat (Fig. 3) lights and/or the remote battery meter (Fig. 4) indicates low voltage.		A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations.
Black smoke exits the tailpipe.		Service the air cleaner.
The engine fails to crank.		A. Try starting at the genset rather than at the remote control. b. Replace fuse F1 on the control panel if it has blown. c. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. d. Recharge the battery. Refer to the battery manufacturer’s recommendations.
The engine cranks but fails to start.		A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Replace fuse F2 (side of control panel) if it has blown. e. Service the air cleaner. f. Secure the spark plug leads on the spark plugs. g. Replace the spark plugs.
There is no electrical power even though the genset runs.		A. Reset tripped circuit breakers. See Powering Equipment. b. Unless there is an automatic power transfer switch, plug the vehicle power cord into the genset power output receptacle (if so equipped) or turn the vehicle power selector switch to its genset position (if so equipped).
The remote battery condition meter indicates low voltage.		A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations.
Eng Cranks But Will Not Start (Genset)		-01 Check: - Spark plugs - Ignition coil - Ignition module -02 Perform checks in step 01
Engine Overfueling (Genset)		-01 Check: - Spark plugs - Fuel pressure at carburetor - Vacuum pull−off - Electric choke heater -02 Perform checks in step 01 - Check: - Governor adjustments - Carburetor adjustments -03 Perform checks in step 02 - Check: - Ignition coil - Ignition module
Engine Unstable (Hunts) (Genset)		-01 Check: - Fuel supply - Fuel Lines for leakage - Loose wire connection -02 Perform checks in step 01 - Check: - Governor linkage for binding - Governor adjustments - Carburetor adjustments
Engine Will Not Crank (Genset)		-01 Check: - Low battery voltage - Terminal connection−loose or dirty - Battery cable size - Starter drive engagement -02 Perform checks in step 01 - Check: - Remote control - Connections on PCB control board - Start solenoid - Starter
High/Low AC Output (Genset)		-01 Check: - Broken or loose wires - Voltage regulator - Transformer regulator - Engine speed - Voltage ad
Blue Exhaust Smoke	1. Incorrect float level in carburetor.	Adjust carburetor float level. Replace carburetor float
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-In)	1. Oil viscosity too light or oil is diluted. 2. Crankcase breather valve is dirty or faulty. 3. Oil leaks. 4. Excessive engine wear. 5. Light loading.
If the genset fails to start		See the Troubleshooting Guide in the Operator’s Manual
Fuel leaks are found		Stop the set immediately, close off the fuel supply and have the leak(s) repaired
Exhaust system for leaks is examined		Stop the set and have the exhaust system repaired immediately
Generator set is excessively noisy		Have it inspected and repaired immediately by an authorized Onan service center

Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.

Common problems

Weakness and Sleepiness
Fix: Get out into fresh air immediately.
Vomiting
Fix: Get out into fresh air immediately.
UNIT STOPS
Cause: . Faulty Ignition 1. See 4 above (CRANKS BUT WON'T START). 2. Out of Fuel 2. Refill fuel tank. 3. Low Oil Level 3. Check oil level. If low or empty, refill to proper level.
Fix: . See 4 above (CRANKS BUT WON'T START). 2. Refill fuel tank. 3. Check oil level. If low or empty, refill to proper level.
UNIT STARTS, BUT STOPS IMMEDIATELY AFTER RELEASING START SWITCH S1
Cause: . Resistor R1 may be open . Check voltage on both sides of R1. With set running, voltage should be 24-32 volts DC.
Fix: . Run Ignition Relay K3 2. Check voltage on both sides of K3. Should be 12 volts. 3. Low Oil Level 3. Check oil level. If low or empty, refill to proper level. 4. S3 Low oil pressure switch may be defective 4. Check S3. Switch should close with set running at 10 Ibs minimum oil pressure.
UNIT RUNS THEN STOPS
Cause: . Low Oil Level . Check oil level. If low or empty, refill to proper level.
Fix: . Check oil level. If low or empty, refill to proper level.
UNIT RUNS BUT SURGES
Cause: . Stuck Choke 2. Governor Not Adjusted Properly
Fix: . See 3 above (CRANKS BUT WON'T START). 2. Readjust governor.
REMOTE RUNNING TIME METER OR GENERATOR LAMP INOPERATIVE
Cause: . Blown Fuse (F1)
Fix: . Replace F1 fuse on control.
Muscular Twitching
Fix: Get out into fresh air immediately.
Low Oil Pressure
Cause: 1. Sticking or binding governor linkage, 2. Incorrect governor adjustment, 3. Faulty governor spring - 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, c. dirt in carburetor 5. Governor mechanism worn excessively, 6. Carburetor icing *Gasoline sets only
Fix: 1a. Clean and lubricate governor linkage 2. Adjust governor speed and Replace governor spring 3. Adjust carburetor main and idle adjustment screws 4b. Adjust carburetor float level 5. Disassemble carburetor and clean all internal passages
High Oil Consumption
Cause: 1. Oil viscosity too light or oil is diluted, 2. Crankcase breather valve is dirty or defective, 3. Oil leaks, 4. Excessive engine wear, 5. Light loading
Fix: 1a. Drain oil and refill with correct viscosity oil 2. Clean crankcase breather and replace if defective 3. Locate source of leak and repair as required 4. See Engine Block Assembly section 5. Don't run set at no load for long periods of time
FAILS TO CRANK
Cause: . Bad Battery Connection 2. Low Battery 3. Faulty Start Solenoid (K1) 4. Faulty Start Switch 5. Blown Fuse (F1)
Fix: . Clean and tighten all battery and cable connections. 2. Check specific gravity. Recharge or replace if necessary. 3A. Check for Battery Voltage at K1 “Il” terminal. 3B. Push start switch. Check start solenoid “S1” terminal voltage to ground. When battery voltage at start solenoid “B-” terminal is present, battery voltage should also appear at “S1” terminal. If not, check K3. 4. Jumper switch (#3 terminal) to ground. If solenoid energizes, replace switch. 5. Replace fuse (F1) on control.
Engine Misfires
Cause: Faulty ignition due to: a. worn or fouled spark plugs, b. worn ignition points., c. incorrect ignition timing, d. faulty ignition coil, e. faulty plug wires.
Fix: 1a. Clean or replace spark plugs 1b. Replace breaker points IC. Set breaker point gap 1d. Test coil and replace if necessary 1e. Test spark plug wires and replace if faulty
Engine Lacks Power
Cause: Faulty ignition due to: a. incorrect ignition timing, b. incorrect spark plug gap 2. Dirty air cleaner 3. Restricted fuel flow due to: a. plugged fuel filter or b. faulty fuel pump 4. Incorrect fuel mixture due to: a. incorrectly adjusted c. dirt in carburetor
Fix: 1a. Adjust breaker point gap 1b. Reset spark plug gap 2. Replace air cleaner 3a. Clean fuel filter 3b. Test fuel pump and repair or replace if faulty 4a. Adjust carburetor main and idle adjustment screws 4b. Adjust carburetor float level 4c. Disassemble carburetor and clean all internal passages
Engine Hunts or Surges
Cause: 1. Sticking or binding governor linkage, 2. Incorrect governor adjustment, 3. Faulty governor spring - 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, c. dirt in carburetor 5. Governor mechanism worn excessively, 6. Carburetor icing *Gasoline sets only
Fix: 1a. Clean and lubricate governor linkage 2. Adjust governor speed and Replace governor spring 3. Adjust carburetor main and idle adjustment screws 4b. Adjust carburetor float level 5. Disassemble carburetor and clean all internal passages
Engine Black Exhaust
Cause: 1. Rich fuel mixture due to: a. dirty air cleaner., b. choke sticking, c. incorrectly adjusted fuel mixture screws d. dirt in carburetor *Gasoline sets only
Fix: 1a. Clean choke and choke linkage 1b. Adjust carburetor idle and main adjustment screws IC. Disassemble carburetor and clean all internal passages

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan NH.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			140B1073	500 hr	Amazon eBay
Fuel filter	Elbow, Fuel Filter Outlet		502-2		Amazon eBay
Oil filter			122B323	200 hr	FridayParts $39.99
Battery			—	30 hr
Belt	Approx. 1/2 inch deflection midway between alternator and flywheel pulleys		511-51		FridayParts $16.70
Coolant			—
Coolant filter			—
Oil	API SE (SD or SD/CC if SE unavailable)	4.0 qt	—	100 hr
Spark plug	Champion N-6 or equivalent; gap .025 in. gasoline, .018 in. gas fuel		—	100 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Months	Notes
Engine oil level	Check	8 hr		Check daily or after every 8 operating hours and add as required; check more frequently on a new or reconditioned engine.
Exhaust system	Check	8 hr		Check visually and audibly for leaks daily, at least every 8 hours of running time.
Exhaust system	Inspect	8 hr		Inspect visually and audibly for leaks daily (at least every eight hours of running time)
Crankcase oil	Change	100 hr		First service — Perform after first 25 hours of operation on new sets (Note 3). Change every 25 operating hours in extremely dusty or dirty conditions.
Polyband air filter (Contractor's)	Clean	25 hr
Cylinder head bolts and valve clearance	Adjust	50 hr		First service — Tighten head bolts and adjust valve clearance after first 50 hours on a new or overhauled engine
Cylinder head torque	Check	50 hr		First service — Recheck torque before engine has run a total of 50 hours
Governor linkage	Clean	50 hr		Clean plastic joints (do not lubricate); inspect for binding, excessive slack and wear
Spark arrester	Clean	50 hr		Periodic clean-out every 50 to 100 operating hours; spin-out or screen type.
Air cleaner element	Check	100 hr		Check at least every 25 hours in extremely dusty or dirty conditions.
Air cleaner element	Clean	100 hr		Remove paper element and clean by tapping against a flat solid object
Engine cooling fins	Clean	100 hr		Check and clean at least every 100 hours of operation.
Reduction gear drive oil	Change	100 hr	6 mo	First service — Drain gear box after first 100 hours and refill; repeat every six months or every 100 hours, whichever is first
Spark arrester muffler	Clean	100 hr		Remove 1/8" pipe plug in bottom of muffler and run set under load for 5 minutes. Then replace pipe plug.
Spark plugs	Clean	100 hr		Check, clean and reset gap; replace plugs showing fouling or electrode erosion.
Breaker arm pivot shaft	Lubricate	200 hr		Place a drop of light oil on breaker arm pivot shaft every 200 operating hours
Breaker points	Replace	200 hr		Change breaker points every 200 hours of operation
Governor linkage	Lubricate	200 hr		Every 200 hours clean the joints and lubricate; inspect for binding, excessive slack and wear.
Oil filter	Change	200 hr		Change the crankcase oil filter every 200 hours
Oil filter	Replace	200 hr		Install filter tight plus 1/4 to 1/2 turn
Spark plugs	Replace	200 hr		Replace plug at least every 200 hours of operation.
Air cleaner element	Replace	500 hr		Standard model generator sets: 400 hours (Note 4). Mobile generator: 200 hours. Contractor's model paper element: 200 hours.
Generator brushes	Check	400 hr		Check every 400 hours that brushes move easily in their holders; remove dust or dirt.
Carbon and lead deposits	Clean	500 hr		Remove after each 500 hours of operation; 10 percent derating required if not removed.
Engine cooling area (fins on cylinder block and cylinder heads)	Clean	1000 hr		Clean at regular intervals, normally every 1000 hours, sooner under dirty operating conditions
Complete reconditioning	Other	5000 hr		Listed under 5000-hour column heading
Battery	Check		1 mo	Monthly: keep case clean and dry, connections clean and tight, maintain electrolyte level.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Camshaft Bearing	0.0015 - 0.008	in
Clearance	Camshaft Bearing	0.0015-0.003	in.
Clearance	Camshaft Bearing Diameter	1.3760 - 1.3770	in
Clearance	Camshaft Bearing Diameter	1.3760-1.3770	in.
Clearance	Camshaft End Play	0.003	in.
Clearance	Camshaft Journal Diameter	1.3740 - 1.3745	in
Clearance	Camshaft Journal Diameter	1.3740-1.3745	in.
Clearance	Camshaft Lift	0.033	in.
Clearance	Camshaft center pin extension from camshaft end	3/4	inch
Clearance	Carburetor float level (float surface nearest gasket from gasket)	1/8 +/- 1/16	in	carburetor inverted
Clearance	Carburetor float level (float to carburetor body)	1/8	inch	carburetor casting inverted
Clearance	Carburetor throttle stop screw clearance to stop pin	1/32	inch	engine operating at no load
Clearance	Choke pull-off diaphragm clearance (choke plate to bottom of carburetor)	0.39-0.43	inches (9.9-10.9 mm)	4 to 18 inches Hg vacuum applied
Clearance	Commutator mica undercut depth below surface	approximately 1/32	inch
Clearance	Connecting Rod Bearing Clearance	0.0005-0.0028	in. (0.013-0.071 mm)
Clearance	Connecting Rod End Play (Ductile Iron)	0.002 - 0.016	in
Clearance	Connecting Rod End Play (Ductile Iron)	0.002-0.016	in.
Clearance	Crankshaft End Play	0.005 - 0.009	in
Clearance	Crankshaft End Play	0.005-0.009	in.
Clearance	Crankshaft Main Bearing	0.0025 - 0.0038	in
Clearance	Crankshaft Main Bearing Journal - Standard Size	1.9992 - 2.000	in
Clearance	Crankshaft Main Bearing Journal - Standard Size	1.9992-2.000	in.
Clearance	Crankshaft Rod Bearing Journal - Standard Size	1.6252 - 1.6260	in
Clearance	Crankshaft Rod Bearing Journal - Standard Size	1.6252-1.6260	in.
Clearance	Cylinder Bore - Standard Size	3.5625 - 3.5635	in
Clearance	Cylinder Bore - Standard Size	3.5625-3.5635	in.
Clearance	Exhaust pipe termination from vehicle gasoline filler spout	3	feet	minimum; more if required by local codes
Clearance	Exhaust system clearance from combustible material	1-1/2	inches	minimum
Clearance	Exhaust system extension beyond vehicle perimeter	1	inch	minimum
Clearance	Flexible fuel line movement allowance	4	inches	to prevent binding, stretching or breaking
Clearance	Front oil seal depth in gear cover	0.97 ± 0.02	inch (24.6 ± 0.5 mm)	from mounting face of cover
Clearance	Gear cover oil seal installation depth	31/32	inch from mounting face of cover
Clearance	Generator cooling air inlet clearance on generator end	1	inch	minimum
Clearance	Governor cup in-and-out travel	7/32	inch	cup held against flyballs when measuring
Clearance	Governor linkage stop pin to carburetor stop boss	3/32	inch	engine stopped, tension on governor ring
Clearance	Main Bearing Clearance	0.0015 - 0.0043	in
Clearance	Main Bearing Clearance	0.0015-0.0043	in.
Clearance	Main Bearing Diameter	2.0015 - 2.0040	in
Clearance	Main Bearing Diameter	2.0015-2.0040	in.
Clearance	New style thin open face gear cover seal installation depth	1-7/64	inches from mounting face of cover
Clearance	Oil Pump Gear Backlash	0.002 - 0.005	in
Clearance	Oil Pump Gear Backlash	0.002-0.005	in.
Clearance	Piston Pin Diameter	0.7500 - 0.7502	in
Clearance	Piston Pin Diameter	0.7500-0.7502	in.
Clearance	Piston Pin in Piston	Thumb Push Fit
Clearance	Piston Pin in Rod	0.0001 - 0.0005	in
Clearance	Piston Pin in Rod	0.0002-0.0007	in.
Clearance	Piston Ring Gap	0.0100-0.0200	in. (0.254-0.508 mm)
Clearance	Piston Ring Groove Width - Top 1	0.0955-0.0965	in.
Clearance	Piston Ring Groove Width - Top 2	0.0955-0.0965	in.
Clearance	Piston Ring Groove Width - Top 3	0.1880-0.1890	in.
Clearance	Piston Ring Groove Width - Top1	0.0955 - 0.0965	in
Clearance	Piston Ring Groove Width - Top2	0.0955 - 0.0965	in
Clearance	Piston Ring Groove Width - Top3	0.1880 - 0.1890	in
Clearance	Piston Ring Side Clearance (top compression ring only)	0.006	in.
Clearance	Piston clearance in cylinder	0.0070-0.0090	in. (0.178-0.229 mm)
Clearance	Piston pin bore out of round (replace piston pin)	0.002	in.
Clearance	Piston to Cylinder, Strut Type (measured below oil-controlling ring, 90 degrees from pin)	0.0015-0.0035	in.
Clearance	Piston to Cylinder, Strut Type (measured below oil-controlling ring, 90° from pin)	0.0015 - 0.0035	in
Clearance	Rod Bearing (Forged Rod)	0.0005 - 0.0023	in

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Capacity	Notes
Engine oil	10W	API SE (SD or SD/CC if SE unavailable)		0°F to 30°F
Engine oil	30	API SE (SD or SD/CC if SE unavailable)		30°F to 90°F
Engine oil	50	API SE (SD or SD/CC if SE unavailable)		Above 90°F
Engine oil	5W	API SE (SD or SD/CC if SE unavailable)		Below 0°F
Engine oil	Good quality detergent oil with API designation SE or SECC; low ash content .03-.85 percent by weight for natural gas or propane fueled engines	API SE or SECC	4.0 U.S. quarts (4-1/2 with filter)	Ambient temperature must be the factor for determining proper SAE oil weight. Do not use oil with designation CD unless also designated SE and certified by the oil manufacturer for gasoline engines.
Engine oil	SAE 30, 40 / 20W-40, 20W-50 / 10W-30, 10W-40	API designation SF or SF/CC; passed MS Sequence Tests (ASTM G-1V)	3.3 L	Capacity with filter 3-1/2 Qt (3.3 L). Single grade oils generally more desirable unless a wide range of temperature is anticipated.
Fuel	High quality, regular grade of gasoline			Gaseous fuel requires above 800 BTU per cubic foot for manual starting; temperature above 30 F (-1 C) for sufficient cranking speed. Full power with gas rated 1,100 BTU or higher.
Fuel	LPG (Propane Liquid Withdrawal)			NHEL model; liquid withdrawal system; supply tank must have a dip tube
Fuel	Lead-Free or Regular Gasoline			NHE (gasoline) model
Fuel	Unleaded or regular grade gasoline			Use regular grade leaded gasoline for the first 25 hours of break-in. Do not use highly leaded premium fuels. LPG/gaseous fuel also supported on combination gas-gasoline sets.
Fuel	unleaded or regular grade gasoline			Use clean, fresh, unleaded or regular grade gasoline. Do not use highly leaded premium fuels. If unleaded is desired, use regular gasoline for the first 25 hours to allow rings to seat.
Gear oil	SAE 50 motor oil or SAE 90 mineral gear oil		1.0 pint US	Reduction gear drive; do not use extreme pressure or hypoid lubricants
Grease	GE Versilube 322-L			Apply light coat on outside diameter of starter helix, inside diameter of gear and unchamfered end of gear
Grease	Mineral grease or petroleum jelly			Coat battery terminals to reduce corrosion and oxidation.
Grease	mineral grease or petroleum jelly			Coat battery terminals to reduce corrosion and oxidation.
Other	water, drinking quality or better			For battery electrolyte; add water, not electrolyte, to maintain level to split level marker.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Breaker Point Removal and Gapping adjustment

Tools: Feeler/thickness gauge, Screwdriver

Remove the cover of the breaker box.
Remove the spark plugs so the engine is easily rotated by hand.
Remove the breaker point mounting screws and install a new set; do not fully tighten yet.
Rotate the engine clockwise by hand until the flywheel mark and the gear cover TC mark align.
Turn the point adjusting cam screw until the point gap is 0.020 inch; tighten the mounting screws.
Turn the flywheel left past the timing marks, then right; points should separate when TC mark aligns with the correct degree mark.
Replace spark plugs.

Breaker Point Replacement and Adjustment adjustment

⚠ Ignition adjustments should be made with the engine in a static condition and cold.

⚠ Make sure feeler gauge is clean and free of any grease, oil or dirt.

Tools: Allen head wrench, Flat thickness gauge (feeler gauge), Hex-head socket and socket wrench

Disconnect negative (-) battery cable at battery terminal.
Remove breaker box cover clip and lift off cover.
Remove spark plugs; turn rotor through-bolt clockwise until breaker point gap is open maximum.
Remove condenser mounting screw and disconnect condenser and ignition leads; lift out condenser.
Remove breaker points mounting screws and lift out point assembly.
Replace condenser and point assembly in reverse order of removal.
Use allen head wrench to adjust set screw to obtain the gap setting specified in Section 2 Specifications.
Measure point gap with a flat thickness gauge; clean points after adjusting.
Timing is set during initial engine assembly and fixed by point gap adjustment; no other adjustment necessary.
Replace point box cover, spark plugs, and spark plug leads.
Connect negative (-) battery cable to negative battery terminal.

Breaker Points and Ignition Timing adjustment

⚠ Make ignition adjustments with the engine stopped and cold. Make sure feeler gauge is clean and free of grease, oil or dirt.

Tools: Feeler gauge / flat thickness gauge, Allen head wrench

Remove cover by loosening screw and lift off.
Turn the engine crankshaft (with rotation) until the maximum breaker point gap is obtained.
Using an allen head wrench, adjust set screw for 0.020 inch (0.51 mm); measure gap with a flat thickness gauge.
Replace point box cover.

Carburetor Adjustment adjustment

⚠ Do not force the needle valves against their seats; this will bend the needle.

If completely out of adjustment, open both needle valves 1 to 1-1/2 turns off their seats to permit starting.
Be sure ignition system works and governor is adjusted; allow engine to warm up.
With no load, turn idle adjustment out until speed drops slightly below normal.
Turn needle in until engine speed returns to normal.
Apply a full load to the engine.
Turn main adjustment in until speed drops slightly below normal.
Turn needle out until speed returns to normal.
Set throttle stop screw to allow 1/32 inch clearance to stop pin at no load.

Carburetor Adjustment (Gasoline) adjustment

⚠ Do not force the needle valves against their seats; this will bend the needle.

Tools: Screwdriver

Be sure the ignition system works and the governor is adjusted; allow the engine to warm up.
Apply a full load to the engine.
Turn the main adjustment in until speed drops slightly below normal, then turn out until speed returns to normal.
With no load, turn the idle adjustment out until speed drops slightly below normal, then in until speed returns to normal.
Set the throttle stop screw to allow 1/32 inch clearance to the stop pin at no load.

Carburetor Mixture Screw Adjustments - Gasoline adjustment

⚠ Forcing the mixture adjustment screws tight will damage the needle and seat; turn in only until light tension is felt.

Tools: Voltmeter, Frequency meter, Load bank, Screwdriver

Stop set and connect voltmeter, frequency meter, and load bank to generator output leads.
Start set and apply full load; verify frequency within 59 ± 2 hertz, adjust governor speed nut if necessary.
Turn main adjustment screw inward until voltage or frequency drops; locate highest point, then turn out an additional 1/4 turn.
Remove load and verify frequency within 62 ± 1 hertz; adjust governor speed nut if necessary.
Turn idle adjustment screw inward until voltage and frequency drop and engine runs rough or hunts; back out for smoothest operation.
Pull governor linkage forward so throttle lever rests against throttle stop screw; adjust stop screw for 55 hertz and 100 (±4.5) volts.
Release governor linkage, set voltage and frequency, adjust governor sensitivity.
Add and remove a full load several times to make certain set does not bog down or hunt.

Carburetor Mixture Screw Adjustments - LP Gas adjustment

⚠ Forcing the mixture adjustment screws tight will damage the needle and seat; turn in only until tension is felt.

Tools: Voltmeter, Frequency meter, Load bank, Screwdriver

Turn mixture screws in until lightly seated for preliminary adjustment.
Turn main adjustment screw out 2-1/2 (±1/4) turns and idle adjustment screw out 1 (±1/4) turn.
Start engine and run about 10 minutes at light load.
Connect voltmeter, frequency meter, and load bank; start set and apply full load; verify frequency within 59 ± 2 hertz.
Turn main adjustment screw inward until voltage/frequency drop, then outward until they drop again; set at highest point.
Remove load and verify frequency within 62 ± 1 hertz; adjust governor speed nut if necessary.
Turn idle adjustment screw inward until voltage/frequency drop and engine runs rough; back out until engine runs smoothly without hunting.
Pull governor linkage forward so throttle lever rests against throttle stop screw; adjust stop screw for 55 hertz and 100 (±4.5) volts.
Release linkage, set voltage and frequency, adjust governor sensitivity; add and remove half load several times.

Choke Adjustment adjustment

⚠ The choke gets very hot during normal operation and can cause severe burns if touched. Do not remove choke cover while the set is operating.

Tools: Screwdriver

Stop set and allow it to cool down before making adjustments.
Remove protective plastic choke cover and loosen heating element cover screws.
Rotate heating element until choke plate is about halfway open.
Slowly rotate cover counterclockwise while tapping the carburetor choke lever until it no longer bounces (fully-closed reference position).
Refer to Table 6-3 for degrees to rotate element cover clockwise from reference position (marks spaced at 5 degrees).
Rotate element cover as specified and tighten cover mounting screws.
Move choke lever back and forth to check smooth operation and automatic return.
Install plastic choke cover and tighten center mounting nut.

Choke Adjustments adjustment

⚠ The choke cover gets very hot during normal operation and can cause serious burns if touched. Do not touch the choke cover while the set is operating.

Loosen the two mounting screws and rotate the choke cover until the correct setting is attained.
Check the setting by starting the engine and observing its operation.
Retighten the mounting screws after adjustment.

Choke Pull-off Diaphragm Adjustment adjustment

Tools: Vacuum source (4 to 18 inches Hg), Measuring gauge

Remove the complete air filter assembly to provide access to the choke plate.
Disconnect diaphragm hose from intake manifold and apply 4 to 18 inches (102 to 457 mm) Hg vacuum to the diaphragm.
Apply light finger pressure against the choke lever to take up all freeplay in the pull-off linkage.
Check alignment of diaphragm stem, pull-off linkage, and slot in choke lever; correct as required.
Measure distance between choke plate and bottom of carburetor; bend diaphragm mounting bracket to obtain 0.39 to 0.43 inches (9.9 to 10.9 mm) clearance.
Move choke lever back and forth to check for free movement; verify choke does not bind or stick.
Remove vacuum supply from diaphragm and install filter assembly on carburetor.

Crankshaft Endplay Check and Adjustment adjustment

Tools: Dial indicator, Torque wrench

After the rear bearing end plate has been tightened to the recommended torque, check the crankshaft endplay.
If there is too much endplay, remove the rear bearing end plate.
Add a shim between the thrust washer and plate.
Reinstall the end plate making sure the thrust washer and shim notches line up with the lock pins.
Torque and recheck the endplay of the crankshaft.

Gaseous Fuel Carburetor Adjustment adjustment

Tools: Screwdriver

Set preliminary settings: 800 BTU gas about six turns open, 1,100 BTU gas 3-1/2 turns open, propane about three turns open; idle screw two turns open.
For manual starting, gas should be above 800 BTU per cubic foot and temperature above 30 F; load disconnected or minimum.
Allow the engine to warm up thoroughly.
Apply full load and turn the load adjust screw in until the engine loses speed from lack of fuel, then slowly back out until it carries full load smoothly.
Remove all load and adjust the idle screw in the same manner; check operation at various loads.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		Standard setting: CR4-AC to X2, S1 to X5	CR4-AC, S1, X1-X6 (transformer secondary taps)	Generator output voltage is adjusted by changing connections to the transformer secondary taps (Table 8-1); adjust to increase or decrease voltage as required.
120	1	2 wire	M1, M2, M4	Single-phase reconnectible, voltage code -3C. Use two-wire service when one load exceeds one-half the rated capacity.
120	1	2 wire, M1 or M2 with M0	M1 or M2, M0	Delta generator, voltage code -5D. M3 terminal not used. Do not use M0 and M3 as a 120-volt circuit; that connection provides approximately 190 volts and could damage 120-volt loads.
120	1	2-wire	M1, M2	3.0AJ single-phase '1R' 120 volt connections; 30 amp; black ungrounded load wire, white grounded load wire.
120/240	1	3 wire	M1, M2, M4	Single-phase reconnectible generator, voltage code -3C. Balance the load for three-wire service. Current for any one output lead must not exceed nameplate rating.
120/240	1	3-wire	M1, M2, M3, M4	5.0 BGA and 6.5 NH single-phase '3CR' 120/240 load wire connections.
240	1	2 wire	M1, M2, M4	Single-phase reconnectible, voltage code -3C.
240	1	2 wire, between any two of M1, M2, M3	M1-M2, M2-M3, or M1-M3	Delta generator, voltage code -5D. The M0 lead is not used.
240	3	3 phase, 3 wire	M1, M2, M3	Delta generator, voltage code -5D. M0 is the neutral wire and is not used for three-phase operation.
240 (higher nameplate voltage); lower nameplate voltage for single-phase	3 (4 wire wye)	M0 grounded neutral; M1, M2, M3 ungrounded	M0, M1, M2, M3	Wye generator, voltage codes -4 and -4X. For single-phase current connect the neutral (white) load wire to M0 and the hot (black) wire to any one of M1, M2 or M3. For three-phase connect separate load wires to M1, M2 and M3.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Common questions

What is the oil capacity of the Cummins/Onan NH?

The Cummins/Onan NH engine has an oil capacity of 3.3 liters.

Which generators use the Cummins/Onan NH engine?

The Cummins/Onan NH powers 1 generator set(s), including Cummins/Onan 6.5 NH.

How often should you change the oil in the Cummins/Onan NH?

The Cummins/Onan NH oil change interval is every 100 hours.

What is a common problem with the Cummins/Onan NH engine?

A commonly reported issue on generators using the Cummins/Onan NH is: Weakness and Sleepiness. Fix: Get out into fresh air immediately..

Cummins/Onan NH Engine

Engine specifications

Generator sets powered by this engine

Troubleshooting

Fault codes

Symptoms & remedies

Common problems

Maintenance schedule

Repair guides

Service intervals

Service specifications

Recommended fluids

Procedures

Voltage reconnection

Common questions