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Cummins/Onan W2C Engine

The Cummins/Onan W2C is a 2-cylinder engine rated at 1800 rpm, producing up to 5.22 kW. It powers generator sets from Cummins/Onan, including the W3M-19. It holds 5.68 L (1.5 gal) of oil and 8.52 L (2.3 gal) of coolant.

Also known as: Onan W2C

Cylinders

1800 rpm

Rated speed

5 kW

Gross power

5.68 L

Oil capacity

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

Engine specifications

Oil capacity	5.68 L
Coolant capacity	8.52 L
Cylinders	2
Rated speed	1800 rpm
Gross power	5 kW

Generator sets powered by this engine

Cummins/Onan W3M-19

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

Common problems

Excessive oil consumption, light blue smoky exhaust
Cause: Poor compression, usually due to leaking valves
Fix: Tighten head gasket and plugs. If still not corrected, return unit to depot for repairs
Engine will not start when cranked
Cause: Faulty ignition (spark plugs)
Fix: Clean, adjust or replace plugs
Low oil pressure
Cause: Oil too light
Fix: Drain, refill with proper oil
Voltage drops under heavy load
Cause: Engine lacks power
Fix: See remedies for engine missing under heavy load
Pinging sound when engine is rapidly accelerated or heavily loaded
Cause: Carbon in cylinders
Fix: Remove carbon
Engine backfires at carburetor
Cause: Lean fuel mixture (carburetor)
Fix: Clean carburetor
Engine misses at all speeds
Cause: Fouled spark plug
Fix: Clean and adjust
Engine misses at light load
Cause: Carburetor idle adjustment set wrong or clogged
Fix: Adjust, clean if needed
Engine misses at heavy load
Cause: Spark plugs defective
Fix: Replace
Voltage unsteady but engine not missing
Cause: Poor commutation or brush contact at slip rings
Fix: See that brushes seat well on commutator, are free in holders, are not worn shorter than 3/4" and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repairing
Light pounding knock
Cause: Connecting rod (short out one spark plug at a time to locate)
Fix: Return unit to depot for repairs
High oil pressure
Cause: Oil too heavy
Fix: Drain, refill with proper oil
Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load
Cause: Fuel mixture too rich (carburetor adjustment)
Fix: Adjust
Sharp metallic thud, especially when cold engine first started
Cause: Low oil supply
Fix: Add oil
Engine runs but A.C. voltage does not build up
Cause: Exciter brushes and commutator
Fix: See that brushes seat well on commutator, are free in holders, are not worn shorter than 3/4" and have good spring tension. If commutator is rough or badly grooved, return unit to depot for repair

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan W2C.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Air cleaner (Donaldson Co. 2xB451)		12118	64 hr	Amazon eBay
Fuel filter	Fuel filter assembly (Weatherhead)		—	256 hr
Oil filter	Oil pump intake screen		—	2048 hr
Belt	Independent Rubber Co. 2300		12906	64 hr	Amazon eBay
Coolant	Clean, alkali-free water; distilled or rain water; anti-freeze if freezing	9.0 quarts	—	8 hr
Oil	Army No. 2104-A (OE) oil, SAE number per lowest temperature	6.0 quarts	—	64 hr
Spark plug	Champion No. 6M, gap .030 in.		—	200 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	Notes
fuel supply	Check	3 hr	Bayonet gage on fuel tank cap; tank holds 3 gallons
air cleaner oil level	Check	8 hr	Refill to level mark with OE oil
crankcase oil	Check	8 hr	Every 8 hours when using diluted oil; change every 64 hours
crankcase oil level	Check	8 hr	Fill to FULL mark on gage
radiator cooling liquid level	Check	8 hr	Add liquid as needed
crankcase oil	Change	50 hr	50 to 100 operating hours with 100 octane leaded fuel
air cleaner	Clean	64 hr	Disassemble, clean and refill with OE oil
crankcase oil	Drain	64 hr	Drain while warm and refill to FULL mark
fan belt	Inspect	64 hr	Adjust or replace as needed
fan hub	Lubricate	64 hr	Fill with OE-30 until oil seeps out
oil can points	Lubricate	64 hr	Throttle shaft bearings, link bearings, door hinges, locks, hood fasteners
carbon and valves	Clean	150 hr	Remove carbon every 100 to 150 operating hours when using leaded fuel
spark plugs	Clean	200 hr	Normal conditions with unleaded fuel
spark plugs	Replace	200 hr	100 octane leaded fuel
carburetor	Drain	256 hr	Drain carburetor and replace drain plugs
engine compression	Test	256 hr	Check by hand crank
exhaust system	Inspect	256 hr	Tighten or replace parts requiring it
fuel sediment bulb and screen	Clean	256 hr
general power unit	Inspect	256 hr	Check for leaks, loose electrical connections and other external items
generator commutator, slip rings and brushes	Inspect	256 hr	Clean, adjust or replace as needed
magneto	Clean	256 hr	Clean distributor; adjust breaker contacts to .015 in.
magneto oil plug	Lubricate	256 hr	Fill opening to overflowing with OE-10
carbon	Clean	1000 hr	Remove carbon, normal unleaded fuel
valves	Adjust	1000 hr	Grind valves each 1000 to 2000 operating hours, unleaded fuel
generator ball bearing	Lubricate	1024 hr	Fill bearing housing with WB-2 grease
magneto impulse coupling	Lubricate	1024 hr	Flush with kerosene, lubricate sparingly with OE-10
crankcase, oil base, oil pump screen and oil lines	Clean	2048 hr	Remove oil base and clean thoroughly

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 bearings	.002 - .0025	in
Clearance	Connecting rod bearing (diameter)	.0015 - .003	in
Clearance	Connecting rod bearing (end play)	.004 - .006	in
Clearance	Crankshaft main bearing (diameter)	.002 - .0025	in
Clearance	Crankshaft main bearing (end play)	.008 - .010	in
Clearance	Crankshaft total end clearance	.008 - .010	in	with feeler gages after installing crankshaft
Clearance	Cylinder bore (actual diameter)	3.003 - 3.004	in
Clearance	Generator armature run-out at bearing	a few thousandths	in	after tightening armature through stud nut
Clearance	Magneto idler gear (bushing to shaft)	.0025 - .003	in
Clearance	Magneto idler gear bushing (end play)	.003 - .005	in
Clearance	Magneto rotor bearings (diameter)	.001 - .002	in
Clearance	Magneto rotor bearings (end play)	.005 - .008	in
Clearance	Oil pump endwise movement of shaft	.002	in	gasket thickness about .008 in. for new pump
Clearance	Piston clearance in cylinder	.003 - .005	in
Clearance	Piston pin in connecting rod	.0002 - .0003	in
Clearance	Piston pin in piston	Hand Push Fit		70 degrees F
Clearance	Piston ring to groove clearance	.001 - .0015	in
Clearance	Timing gear backlash	.002 - .005	in	check at all positions of camshaft gear
Clearance	Valve seat width	.032 - .078	in
Clearance	Valve stem clearance in guide (exhaust)	.0025 - .003	in
Clearance	Valve stem clearance in guide (intake)	.002 - .003	in
Gap	Magneto breaker contact gap	.015	in	contacts wide open
Gap	Piston ring gap	.008 - .015	in	squared in cylinder
Gap	Spark plug gap	.030	in
Other	Mica undercut (commutator)	1/32	in	after refinishing commutator
Other	Throttle stop screw setting	100	volts	governor arm held in closed position by hand
Pressure	Oil by-pass valve setting	15	psi	minimum gage pressure at normal operating temperature
Pressure	Oil pressure, minimum	15	psi	engine at normal temperature
Resistance	Generator output voltage regulation	within 10	percent	no load to full load, at normal operating temperature
Temperature	Generator full load temperature rise	50	degrees C	not to exceed
Torque	Cylinder head nuts	50	foot-pounds	tighten evenly from center nut toward ends; retighten after 30 minutes running
Valve clearance	Valve tappet clearance (exhaust)	.010 - .012	in	engine cold, No. 1 piston at top center
Valve clearance	Valve tappet clearance (intake)	.008 - .010	in	engine cold, No. 1 piston at top center
Voltage	A.C. voltmeter reading, full load	115	volts	normal operating temperature, unity power factor
Voltage	A.C. voltmeter reading, no load	131	volts	normal operating temperature
Voltage	Output voltage range	115 - 131	volts	unity power factor load

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	Capacity	Notes
Coolant	Clean, alkali-free water; distilled or rain water; standard anti-freeze if freezing	9.0 quarts	Fill to level even with top of baffle plate; never use kerosene or distillate as anti-freeze
Engine oil	OE, Army No. 2104-A; SAE 30	6.0 quarts	SAE 30 above 32 F; SAE 10 between 0 and 32 F; SAE 10 diluted with 10% kerosene below 0 F; above 32 F ambient_min 32F
Engine oil	SAE 10 diluted with 10% kerosene		Below 0 F; mix 1 pint kerosene with each 5 quarts SAE 10 oil; never add kerosene alone
Fuel	Gasoline, 68 to 74 octane	3.0 gallons	Fuel tank capacity 3 gallons; do not fill entirely full with cold gasoline
Grease	CG grease		Magneto cam oil pad
Grease	WB-2 general purpose grease		Generator ball bearing housing; pack well into lower half of bearing
Other	OE-30		Fan hub lubrication until oil seeps out on shaft

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

Procedures

Carburetor Adjustment adjustment

⚠ Do not turn either needle tightly into its seat or seat may be damaged

Tools: Screwdriver

Run engine to normal operating temperature.
With 1500 to 3000 watts load, turn main jet needle out 3 turns.
Turn main jet needle in until engine loses power and speed.
Turn needle out slowly until engine regains maximum power and speed.
With no load, turn idle jet needle in until engine loses considerable speed.
Turn idle jet needle out until engine runs smoothest.
Approximate start: turn both needles in, then out about 2-1/2 turns.

Fan Belt Adjustment adjustment

⚠ Do not use a fan belt until it breaks

⚠ Too tight a belt causes unnecessary wear on fan bearing

Tools: Wrenches

Loosen the cap screws which hold the fan bracket.
Raise or lower the bracket to adjust belt tension.
Correct tension allows one side of belt pushed inward about 1/4 in. midway between pulleys.
Tighten the cap screws securely.

Governor Adjustment adjustment

⚠ If no-load and full-load voltages cannot be kept within limits, engine or generator brush adjustment needs attention

Tools: Screwdriver, wrenches, A.C. voltmeter (control panel)

Run power unit at normal operating temperature with no load.
Loosen main adjusting stud locknut.
Turn adjusting nut on stud to obtain correct generated voltage.
Turn nut clockwise to raise voltage, counterclockwise to lower.
Check voltage at full 3 kw resistance load; should not drop below 115 volts.
Adjust sensitivity adjusting stud to eliminate hunting.
Tighten the locknut.

Magneto Breaker Contact Adjustment adjustment

⚠ Do not crank engine while gear housing is off the magneto

Tools: Feeler gage .015 in., Screwdriver

Remove distributor cap and inspect breaker contacts.
Clean pitted or eroded contacts, file pyramids square.
Loosen screw holding stationary contact bracket.
Move bracket by turning eccentric headed screw in open slot.
Adjust gap to .015 in.
Tighten holding screw and recheck gap.
Work CG grease into cam oil pad and reinstall.

Timing the Magneto adjustment

⚠ Do not crank engine while gear housing is off the magneto

Tools: Hand crank, Screwdriver, wrenches

Remove No. 1 spark plug (nearer radiator).
Hold thumb over plug hole and crank slowly until compression felt.
Continue cranking until flywheel timing mark aligns with T.C. mark on crankcase.
Turn magneto gear in normal direction until impulse coupling just trips.
Distributor arm must point toward No. 1 tower.
Install magneto gear without turning distributor from position.
Crank engine slowly and note if coupling trips at timing marks.
If not, loosen magneto flange cap screws and turn frame slightly.

Valve Tappet Adjustment adjustment

⚠ Reassemble using new gasket if available

⚠ Magneto must be retimed after installation

Tools: Feeler gages .006, .008, .010 in., Torque indicating wrench

Remove magneto and valve tappet inspection plate.
Tighten all cylinder head nuts to 50 foot-pounds if torque wrench available.
Crank engine until No. 1 valve closes and top center marks coincide.
Loosen cap screw in No. 2 exhaust lifter enough to push lever inward.
Insert .008 in. feeler gage between cam surface and lifter.
Pull lever outward without pinching feeler and tighten cap screw.
Recheck: .008 in. passes, .010 in. does not pass.
Adjust No. 1 intake lifter with .006 in. and .008 in. feelers.

Cleaning the Air Cleaner maintenance

Tools: Air hose

Remove thumb nut and lift cleaner from power unit.
Lift cover and element assembly from the cup.
Clean old oil and sediment from the cup.
Clean element by sloshing up and down in cleaning fluid or gasoline.
Allow element to dry or dry with air hose.
Fill cup to level mark with clean oil same as crankcase oil.
Reassemble and install cleaner, tightening thumb nut securely.

Preparing the Power Unit for Storage maintenance

⚠ Plug exhaust outlet with a wood plug to prevent entrance of moisture or small animals

Tools: Hand crank

Drain fuel from tank and filter bowl, then run engine until it stops.
Drain all oil from oil base while engine is warm, replace drain plug.
Drain cooling system, leave caps on fuel tank, radiator and oil filler.
Remove spark plugs, pour two tablespoonfuls OE-30 oil in each cylinder, crank several revolutions, replace plugs with gaskets.
Clean generator brushes, holders, commutator and slip rings with clean cloth; do not coat with grease.
Disassemble and clean air cleaner, dip element in OE-30 oil, reassemble without oil in cup.
Wipe exposed parts and coat those liable to rust with a film of grease.
Oil throttle control link joints with OE-50 oil, plug exhaust outlet, install side panels and canvas cover.

Returning Stored Power Unit to Service maintenance

Remove all protective grease coatings and wipe unit clean.
Inspect carefully for damage and correct it.
Remove the plug from the exhaust outlet.
Remove, clean and adjust spark plugs; crank engine several revolutions to distribute oil.
Clean magneto distributor cap and breaker contacts; install new spark plug cables if needed.
Examine fan belt, adjust or install new one as needed.
Examine radiator hose, install new hose if needed.
Check for leaks of gasoline, water and oil after filling; correct all leaks before starting.

Spark Plug Service maintenance

Tools: Spark plug wrench

Remove the spark plugs.
Clean and inspect for cracked or badly eroded porcelain or electrodes.
Discard any plug not in good condition and replace with Champion 6M.
Adjust gap to .030 in.
Make sure gaskets are in place when installing.
Tighten securely.

Starting the Power Unit operation

⚠ Do not spin or push down on the crank

⚠ Do not overchoke

Tools: Hand starting crank

See that circuit breaker is in OFF position.
Pull out choke button as required by temperature; do not overchoke.
Remove starting crank and insert through hole below radiator.
Be sure crank engages positively with crankshaft ratchet.
Crank with a strong, quick, upward pull.
When engine starts, push choke button part way in.
Gradually push choke button entirely in as engine warms up.

Stopping the Power Unit operation

⚠ Do not run power unit with canvas cover on

Disconnect load by throwing circuit breaker handle to OFF position.
Press the STOP button firmly until engine has entirely stopped.
Keep canvas cover installed when not to be operated within a few hours.

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 W2C?

The Cummins/Onan W2C engine has an oil capacity of 5.68 liters.

Which generators use the Cummins/Onan W2C engine?

The Cummins/Onan W2C powers 1 generator set(s), including Cummins/Onan W3M-19.

How often should you change the oil in the Cummins/Onan W2C?

The Cummins/Onan W2C oil change interval is every 64 hours.

What is a common problem with the Cummins/Onan W2C engine?

A commonly reported issue on generators using the Cummins/Onan W2C is: Excessive oil consumption, light blue smoky exhaust. Cause: Poor compression, usually due to leaking valves. Fix: Tighten head gasket and plugs. If still not corrected, return unit to depot for repairs.