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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	Cause	Remedy
F1	Engine Does Not Crank — Control fuse F1 may be open	Control fuse F1 may be open	Check fuse F1. Replace if open with Onan supplied fuse only
R4	Engine Does Not Crank — Circuit breaker tripped (R4)	Circuit breaker tripped (R4)	Wait for circuit breaker to return to local ambient temperature to reset
F2	Engine Cranks But Does Not Start — Fuse F2 has blown (Beginning Spec F)	Fuse F2 has blown (Beginning Spec F)	Replace the fuse
K6	Engine Cranks But Does Not Start — Relay K6 is faulty (Beginning Spec F)	Relay K6 is faulty (Beginning Spec F)	Replace Relay K6 if there is cranking voltage at terminals 87 and 85, but not at terminal 30 when cranking

Symptoms & remedies

Symptom	Cause	Remedy
Engine Misfires	Faulty ignition due to worn or fouled spark plugs	Replace spark plugs
Engine Misfires	Faulty ignition due to worn breaker points	Replace breaker points
Engine Misfires	Faulty ignition due to incorrect ignition timing	Set breaker point gap
Engine Misfires	Faulty ignition due to faulty ignition coil	Test coil and replace if necessary
Engine Misfires	Faulty ignition due to faulty plug wires	Test spark plug wires and replace if faulty
Engine Misfires	Faulty ignition due to faulty condenser	Replace condenser
Engine Misfires	Faulty ignition due to faulty ignition module (electronic ignition)	See Testing Ignition Module
Engine Misfires	Lean fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor main and idle adjustment screws
Engine Misfires	Lean fuel mixture due to incorrect float level	Adjust carburetor float level
Engine Misfires	Lean fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Engine Misfires	Lean fuel mixture due to vacuum leak	Locate leak and correct as required
Engine Misfires	Contaminated fuel	Drain fuel tank and refill with fresh fuel
Engine Misfires	Carburetor icing	In cold weather, place air preheater in winter position
Engine Backfires	Faulty ignition due to incorrect ignition timing	Adjust breaker point gap
Engine Backfires	Faulty ignition due to incorrect spark plug gap	Reset spark plug gap
Engine Backfires	Faulty ignition due to faulty condenser	Replace condenser
Engine Backfires	Lean fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor main and idle adjustment screws
Engine Backfires	Lean fuel mixture due to incorrect float level	Adjust carburetor float level
Engine Backfires	Lean fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Engine Backfires	Mechanical damage to engine	See Engine Block Assembly section
Engine Lacks Power	Faulty ignition due to incorrect ignition timing	Adjust breaker point gap
Engine Lacks Power	Faulty ignition due to incorrect spark plug gap	Reset spark plug gap
Engine Lacks Power	Dirty air cleaner	Replace air cleaner
Engine Lacks Power	Restricted fuel flow due to plugged fuel filter	Clean fuel filter
Engine Lacks Power	Restricted fuel flow due to faulty fuel pump	Test fuel pump and repair or replace if faulty
Engine Lacks Power	Incorrect fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor main and idle adjustment screws
Engine Lacks Power	Incorrect fuel mixture due to incorrect float level	Adjust carburetor float level
Engine Lacks Power	Incorrect fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Engine Lacks Power	Incorrect fuel mixture due to vacuum leak	Repair vacuum leak
Engine Lacks Power	Exhaust system blocked or restricted	Locate and remove cause of blockage
Engine Lacks Power	Incorrect valve tappet clearance	Adjust valve tappets (see Engine Block Assembly section)
Engine Lacks Power	Excessive engine wear or damage to engine	See Engine Block Assembly section
Engine Lacks Power	Carburetor air preheater set incorrectly	In hot weather, place air preheater in summer position
Engine Lacks Power	Excessive carbon buildup	Disassemble and scrape carbon
Engine Lacks Power	No-load speed set too low	Adjust governor
Engine Overheats	Restricted airflow due to dirt or debris blocking air inlet or outlet	Clear away any debris that may restrict airflow to set; Do not use compartment for storage area
Engine Overheats	Dirt or oil covering engine cooling fins	Clean away all dirt and oil from engine cooling fins
Engine Overheats	Incorrect ignition timing	Adjust breaker point gap
Engine Overheats	Lean fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor main and idle adjustment screws
Engine Overheats	Lean fuel mixture due to incorrect float level	Adjust carburetor float level
Engine Overheats	Lean fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Black Exhaust Smoke	Rich fuel mixture due to dirty air cleaner	Replace air cleaner
Black Exhaust Smoke	Rich fuel mixture due to choke sticking	Clean choke and choke linkage
Black Exhaust Smoke	Rich fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor idle and main adjustment screws
Black Exhaust Smoke	Rich fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Engine Hunts or Surges	Sticking or binding governor linkage	Clean and lubricate governor linkage
Engine Hunts or Surges	Incorrect governor adjustment	Adjust governor speed and sensitivity
Engine Hunts or Surges	Faulty governor spring	Replace governor spring
Engine Hunts or Surges	Incorrect fuel mixture due to incorrectly adjusted fuel mixture screws	Adjust carburetor main and idle adjustment screws
Engine Hunts or Surges	Incorrect fuel mixture due to incorrect float level	Adjust carburetor float level
Engine Hunts or Surges	Incorrect fuel mixture due to dirt in carburetor	Disassemble carburetor and clean all internal passages
Engine Hunts or Surges	Governor mechanism worn excessively	See Engine Block Assembly section
Engine Hunts or Surges	Carburetor icing	In cold weather, place air preheater in winter position
Engine Hunts or Surges	Faulty ignition condenser	Replace condenser
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-in)	Oil viscosity too light or oil is diluted	Drain oil and refill with correct viscosity oil
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-in)	Crankcase breather valve is dirty or defective	Clean crankcase breather and replace if defective
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-in)	Oil leaks	Locate source of leak and repair as required
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-in)	Excessive engine wear	See Engine Block Assembly section
High Oil Consumption (Note: New engines sometimes have high oil consumption during break-in)	Light loading	Don't run set at no-load for long periods of time
Low Oil Pressure	Oil viscosity too light or oil is diluted	Drain oil and refill with correct viscosity oil
Low Oil Pressure	Low oil level	Add oil as required
Low Oil Pressure	Low oil pressure switch defective	Replace oil pressure switch (see Engine Block Assembly section)
Low Oil Pressure	Faulty oil bypass valve	Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section)
Low Oil Pressure	Excessive engine wear or defective oil pump	See Engine Block Assembly section
Engine Does Not Crank	If engine cranks at set but not at remote control panel, fault is due to PC board P2/J2 connection not secure	Ensure that wiring harness jack connections are fully seated to PC board
Engine Does Not Crank	If engine cranks at set but not at remote control panel, fault is due to open circuit in remote control	Check for continuity and correct if circuit is open
Engine Does Not Crank	If engine cranks at set but not at remote control panel, fault is due to remote start switch faulty	Replace remote start control switch
Engine Does Not Crank	If engine cranks at remote control panel but not at set, fault is due to faulty S1 switch	Replace PC board A1
Engine Does Not Crank	Insufficient voltage for cranking due to battery not charged	Check condition of battery and recharge or replace
Engine Does Not Crank	Insufficient voltage for cranking due to terminal connections loose or dirty	Clean and tighten all connections at battery, K1 start solenoid, and starter motor, VR2 battery charge regulator
Engine Does Not Crank	If battery voltage is present at terminal S on the start solenoid when S1 is placed in START position, fault is due to K1 relay not grounded	Tighten solenoid bracket mounting screw
Engine Does Not Crank	If voltage is not present at terminal S on the start solenoid when S1 is placed in START position, fault is due to open circuit between K1 relay and control PC board	Check for continuity and correct if circuit is open
Engine Cranks But Does Not Start	Faulty ignition due to worn or fouled spark plugs, worn ignition points, incorrect ignition timing, faulty plug wires, faulty condenser, or faulty electronic module	Refer to Ignition System (Section 6) for test and service procedures
Engine Cranks But Does Not Start	Faulty fuel system due to low fuel level in tank, supply valve not open, sticking choke, faulty fuel pump, or carburetor mixture screws incorrectly adjusted	Refer to Fuel System (Section 6) for test and service procedures
Engine Cranks But Does Not Start	If battery voltage is not present at positive (+) terminal T1 ignition coil when S1 is placed in START position, fault is due to open circuit between T1 coil and control	Check for continuity and correct if circuit is open
Engine Starts But Stops When Start Switch is Released	Low oil pressure switch S2 not closing due to low oil level	Check oil level and add oil if low

Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing. Showing the first 80 of 423 entries.

Common problems

Engine does not crank
Cause: If engine cranks at set but not at remote control panel, fault is due to open circuit in remote control
Fix: Check for continuity and correct if circuit is open
Engine starts but stops when start switch is released
Cause: Low oil pressure switch not closing due to low oil level
Fix: Check oil level and add oil if low
Engine lacks power
Cause: Faulty ignition due to incorrect ignition timing
Fix: Adjust breaker point gap
Engine misfires
Cause: Faulty ignition due to worn or fouled spark plugs
Fix: Clean or replace spark plugs
Engine black exhaust
Cause: Restricted airflow due to dirt or debris blocking air inlet or outlet
Fix: Clear away any debris that may restrict airflow to set. Do not use compartment for storage area
Engine hunts or surges
Cause: Sticking or binding governor linkage
Fix: Clean and lubricate governor linkage
Engine starts and runs; then stops. Set restarts immediately or set restarts after cooling down
Cause: Fuel level is below generator set fuel pickup tube or oil level is low
Fix: Check fuel and oil levels and refill as necessary
Engine cranks but does not start
Cause: Faulty ignition due to worn or fouled spark plugs, worn ignition points, incorrect ignition timing, or faulty plug wires
Fix: Refer to Ignition System section for test and service procedures
Engine backfires
Cause: Faulty ignition due to incorrect ignition timing
Fix: Adjust breaker point gap
Run lamp, time meter, or battery condition meter does not operate
Cause: Open circuit between terminal 6 or remote connector plug and terminal 6 on Start/Run/Stop switch
Fix: Check for continuity and correct if circuit is open
No AC Output Voltage — This condition may cause the generator set to stop when the Start switch is released
Cause: Open circuit breaker
Fix: Locate cause of overload and correct as required. Reset breaker
Low oil pressure
Cause: Oil viscosity too light or oil is diluted
Fix: Drain oil and refill with correct viscosity oil
Low battery
Cause: Weak or discharged battery; generator set charger will not recharge a battery that is in a very low state of charge
Fix: Connect a separate battery charger to bring battery up to full charge
High oil consumption (Note: New engines sometimes have high oil consumption during break-in)
Cause: Oil viscosity too light or oil is diluted
Fix: Drain oil and refill with correct viscosity oil
AC Output Voltage Too Low Or Too High
Cause: Engine governor incorrectly adjusted
Fix: Refer to Governor section

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	eBay $19.00 FridayParts $39.99
Battery			—	30 hr
Belt	Approx. 1/2 inch deflection midway between alternator and flywheel pulleys		511-51		eBay 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		Maintenance schedules recommend inspection every eight hours by owner/operator for RV generator set exhaust systems.
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.
Spark arrester/muffler, screen type	Clean	50 hr		Remove and scrape clean or replace screen; may be blown clean with compressed air. Every 50 operating hours.
Spark arrester/muffler, spin-out type	Clean	50 hr		Remove pipe plug in bottom of muffler and run set for 5 minutes; replace plug. Every 50 hours of set operation.
Spark arresters	Clean	50 hr		Spark arresters should be cleaned every 50 to 100 hours; routine cleaning during servicing is good safety practice.
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.
Stainless steel spark arrester screen	Replace	500 hr		For units using specially designed stainless steel screens.
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.
Flexible fuel lines	Replace		60 mo	Replace every five years as a precautionary measure; check at each service.

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 gear cover oil seal installation depth	1-1/32	in	rear spring side of casing from gear cover mounting face
Clearance	Front oil seal depth in gear cover	0.97 ± 0.02	inch (24.6 ± 0.5 mm)	from mounting face of cover
Clearance	Fuel injection pump installation dimension	3.260	in	new camshaft; instead of 3.254
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.

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
Coolant	Ethylene glycol base anti-freeze mixed with water			Do NOT use straight 100% ethylene glycol. Normal mixture approximately 50% anti-freeze and 50% water; ratio varies with ambient temperature.
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	ASTM 2-D or 1-D diesel fuel	Cetane number 45		Use Number 1-D diesel fuel when ambient temperatures are below 32 F (0 C) or during long periods of light load/cyclic operation.
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

Adjust anti-dieseling solenoid adjustment

With set stopped, turn lever counterclockwise; set screw so plates are closed but not binding.
Check lever has approximately 30 degrees travel counterclockwise from vertical.
Start set; lever should rotate approximately 60 degrees clockwise from stopped position.
Check solenoid plunger is fully seated.
If not, adjust distance between plunger and lever arm; repeat steps.

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.

Carburetor adjustment for 6.5 NH RV adjustment

Turn idle mixture screw out 3/4 to 1 turn from seated.
Turn main mixture screw 1-1/2 to 1-3/4 turns out from seated.
Start set; adjust governor spring for 1860 RPM no load (62 Hz or 130 volts).
Hold governor arm so throttle lever rests on stop; adjust idle stop screw to 1500 RPM (50 Hz or 100 volts); release.
Adjust idle mixture screw to highest RPM or voltage; readjust governor spring to 1860 RPM no load.
Apply full load; adjust main mixture screw to highest RPM or voltage; readjust governor spring to 1770 RPM full load.
Remove and add load several times to check hunting; readjust governor spring if required.

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.

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	single	2 wire		Set is reconnectable for 120 volt, 2 wire service.
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.
120/240	single	3 wire		Set is reconnectable for 120/240 volt, 3 wire service.
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	single	2 wire		Set is reconnectable for 240 volt, 2 wire service.
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: Engine does not crank. Cause: If engine cranks at set but not at remote control panel, fault is due to open circuit in remote control. Fix: Check for continuity and correct if circuit is open.

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