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Cummins/Onan DJB Engine

The Cummins/Onan DJB is a 1.04 L 2-cylinder air-cooled engine rated at 2400 rpm, producing up to 10.9 kW. It holds 3 L (0.8 gal) of oil.

Also known as: ONAN DJB

1.04 L

Displacement

Cylinders

2400 rpm

Rated speed

10 kW

Gross power

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

Engine specifications

Oil capacity	3.0 L
Displacement	1.04 L
Cylinders	2
Aspiration	Air-cooled
Rated speed	2400 rpm
Gross power	10 kW

Generator sets

No generator set in our catalog cites this exact engine designation yet; its specifications and fault codes are documented here.

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

Troubleshooting

Fault codes

Code	Meaning	Remedy
98-4001	Engine is not getting fuel.	Prime the fuel system. Check fuel supply and fuel solenoid. If necessary, check for fuel tank empty, shutoff valves binding, linkage loose or broken wires, fuel lines kinked, loose connections, clogged fuel filters, and transfer pump.

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

Common problems

Worn or sticking piston rings EXCESSIVE OIL CONSUMPTION, LIGHT BLUE SMOKY EXHAUST
Fix: Check compression. Clean or replace ring: a
Worn oil pump Low Oi PRESSURE
Fix: Replace pump
Worn bearings Low Oi PRESSURE
Fix: Rebuild engine
VOLTAGE DROPS UNDER HEAVY LOAD
Cause: Engine lacks power, Poor compression, Faulty injection, Dirty air cleaner, Restricted exhaust line
Fix: See remedies for engine misfires, Tighten cylinder head and glow plug. If still not corrected, grind the valves. Replace piston rings, if necessary., Check the fuel system. Clean, adjust or replace parts necessary, Clean
Unusual noises, loss of power, etc.
Fix: Contact your ONAN dealer.
Unusual noises, loss of power
Fix: Contact your Onan dealer
TAPPING SOUND
Cause: Valve clearance too great, Broken valve spring
Fix: Adjust. Replace faulty valve system, Install new spring
Sticking compression ring
Fix: Replace
SHARP METALLIC THUD, ESPECIALLY WHEN COLD ENGINE FIRST STARTED
Cause: Low oil supply, Oil badly diluted
Fix: Add oil, Change oil
Overload 10
Overheating
Cause: Dirty cooling surfaces, operating without the engine air housing, poor air circulation, improper lubrication, wrong injection timing and engine overload
Oil too heavy LOW OIL CONSUMPTION
Fix: Replace with lighter oil
OIL SYSTEM
Cause: [Diluted oil due to leaky fuel transfer pump diaphragm. Faulty cylinder oil control.
Fix: Rebuild or replace pump if diaphragm is leaking. Inspect rings and cylinder walls for issues related to faulty cylinder oil control.
Oil supply low Low Oi PRESSURE
Fix: Check cause: of oil consumption. Governor incorrectly adjusted.
Oil by-pass stuck open Low Oi PRESSURE
Fix: Clean by-pass valve

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

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Check air cleaner every 50 hours; clean element and retainer in petroleum-base solvent, dry and oil		140-0636	50 hr	Amazon eBay
Fuel filter	Replace primary fuel filter every 600 hours		122-0325	600 hr	Amazon eBay $75.00 NAPA $35.18
Oil filter	Replace oil filter every 200 hours; coat filter gasket and turn on finger tight plus 1/2 turn		122-0185	200 hr	Amazon Amazon eBay $19.55 eBay NAPA $12.88
Battery	Check battery every 200 hours; maintain electrolyte level, keep case clean and dry, coat terminals		—	200 hr
Oil	Change crankcase oil every 100 hours; every 50 hours in extremely dusty or dirty conditions. Capacity includes 1/2 qt for the oil filter	3.31 L	—	100 hr

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

Repair guides

Step-by-step procedures compiled from the Cummins/Onan service manual for this engine.

Service intervals

Item	Action	Hours	Notes
Engine	Inspect	8 hr	Operator Maintenance Schedule; hour columns 8/50 side of table
Engine oil level	Check	8 hr	First service — During break-in, check at least every 8 operational hours
Exhaust system	Inspect	8 hr
Fuel	Check	8 hr	Water or foreign material in fuel can ruin injection system
Fuel supply	Check	8 hr	See Note 1
Air cleaner	Check	50 hr	Wash filter element; replace if damaged
Air cleaner element	Clean	50 hr	Check after each 50 hours of operation
Battery condition	Check	50 hr	See Note 2
Crankcase oil	Change	100 hr	First service — Drain and replace crankcase oil after first 50 hours; drain while engine is still hot
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 bolts	Adjust	50 hr	First service — After first 50 hours of operation, retighten cylinder head bolts and check valve clearance
Cylinder head bolts	Check	50 hr	First service — Tighten head bolts and adjust valve clearance after first 50 hours on new or overhauled engine
Fuel condensation traps in lines and filters	Drain	50 hr	See Note 1
Oil level	Check	50 hr	See Figure 2
Oil-wetted-foam type air cleaner	Clean	50 hr	Wash in clean fuel; moisten with clean crankcase grade oil
Valve clearance	Adjust	50 hr	First service — After first 50 hours on new or overhauled engine
Battery Electrolyte Level	Check	100 hr
Governor Linkage	Clean	100 hr	Every 100 hours; clean plastic joint only, steel joint with graphite
Oil-bath type air cleaner	Clean	100 hr	Thoroughly clean and put in fresh oil
Primary & Secondary Fuel Filter	Clean	100 hr
Fuel Sediment Bowl	Drain	200 hr
Oil Filter	Replace	200 hr	More often under extremely dusty conditions
Valve Clearance	Check	200 hr	Critical Maintenance Schedule
Generator armature, ball bearing, collector rings, commutator, brushes	Inspect	400 hr	Normal maintenance procedure
Air cleaner cartridge	Replace	500 hr	Install new cartridge at least every 500 hours
Breather standpipes	Clean	500 hr	Crankcase breather pipe must be cleaned after every 500 hours
Crankcase Breather	Clean	500 hr
Injection Nozzles	Check	500 hr
Rocker Box Oil Line Holes	Clean	500 hr
Start-disconnect circuit	Check	500 hr
Valve clearances	Check	500 hr
Primary Fuel Filter	Replace	600 hr	Spec S and later
Primary fuel filter	Change	600 hr
Cooling Fins / Cooling Area	Clean	1000 hr	More often under dirty operating conditions
Engine	Clean	1000 hr
Engine cooling area	Clean	1000 hr	More often under dirty operating conditions
Engine cooling area (fins)	Clean	1000 hr	Normally every 1000 hours, more often under dirty operating conditions
Oil Base	Clean	1000 hr	Remove and clean oil base
Valves	Inspect	1000 hr	Inspect valves and grind if necessary
Holes in rocker box	Clean	2000 hr

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	Brush wear limit (replace)	5/8	in
Clearance	Cam tappet hole diameter (prior to Spec P)	.7505-.7515	in	prior to Spec P
Clearance	Camshaft bearing clearance limit	.0012-.0037	in
Clearance	Camshaft bearing clearance limit	0.0012 - 0.0037	in
Clearance	Camshaft bearing journal diameter, front	2.500 - 2.505	in
Clearance	Camshaft bearing journal diameter, rear	1.1875 - 1.1880	in
Clearance	Camshaft end play	.007 - .039	in
Clearance	Camshaft end play	.007-.039	in
Clearance	Camshaft end play	0.007 - 0.039	in
Clearance	Clearance in cylinder (begin Spec P)	.0055-.0075	in	90 degrees to pin, just below oil ring
Clearance	Clearance in cylinder (prior to Spec P)	.0050-.0070	in	90 degrees to pin, just below oil ring
Clearance	Collector ring run-out	0.002	in	compared to generator bearing
Clearance	Commutator and slip ring run-out	.002	in.	less than
Clearance	Commutator mica undercut	1/32	in.	under the bars
Clearance	Connecting rod bearing clearance	.001-.0033	in
Clearance	Connecting rod bushing clearance	.0002-.0007	in
Clearance	Connecting rod bushing clearance	0.0002 - 0.0007	in
Clearance	Connecting rod end play	.002-.016	in
Clearance	Connecting rod large bearing bore diameter (w/o bearing)	2.1871-2.1878	in
Clearance	Connecting rod large bearing to crankshaft clearance	0.001 - 0.003	in
Clearance	Connecting rod small bushing bore diameter (w/o bushing)	1.044-1.045	in
Clearance	Crankshaft connecting rod journal diameter	2.0597-2.0605	in
Clearance	Crankshaft end play	.010-.018	in
Clearance	Crankshaft end play	0.010 - 0.015	in
Clearance	Crankshaft end play	0.010-0.015	in
Clearance	Crankshaft main bearing clearance (DJB)	0.0014 - 0.0049	in
Clearance	Crankshaft main bearing clearance (DJC)	0.0024 - 0.0049	in
Clearance	Crankshaft main bearing journal diameter	2.2487-2.2445	in
Clearance	Cylinder bore	3.2495 - 3.2505	in	less than 0.001 out-of-round
Clearance	Cylinder bore limits	3.2195-3.2505	in
Clearance	Exhaust valve stem diameter	.3405-.3415	in
Clearance	Governor cup center pin distance from camshaft gear	25/32	in
Clearance	Intake valve clearance in guide	.0015-.0030	in
Clearance	Intake valve stem diameter	.3405-.3410	in
Clearance	Main bearing clearance (original)	.002-.0033	in
Clearance	Main bearing clearance (replacement)	.0014-.0052	in
Clearance	Oil pump gear lash	0.005	in
Clearance	Piston clearance to cylinder wall	.0050-.0070	in	prior to Spec P
Clearance	Piston clearance to cylinder wall	.0055-.0075	in	Spec P and later
Clearance	Piston clearance to cylinder wall	0.0050 - 0.0070	in
Clearance	Piston pin fit	Thumb Push Fit		room temperature
Clearance	Piston ring end gap	0.010 - 0.020	in
Clearance	Piston ring groove width 2nd	.0965-.0975	in
Clearance	Piston ring groove width 3rd	.0965-.0975	in
Clearance	Piston ring groove width top	.097-.098	in
Clearance	Ring gap	.010-.020	in
Clearance	Rod bearing clearance	.001-.0033	in
Clearance	Shim thickness	.006 to .052	in.
Clearance	Shutter end thrust clearance	1/32	in	not more than
Clearance	Starter armature end play	0.005 - 0.030	in
Clearance	Starter armature end play	0.005-0.030	in
Clearance	Valve clearance	.020 (0.51), .018 (0.33), .011 (0.28), .016 (0.41), .017 (0.43), .017 (0.43)	inch (mm)	engine at room temperature about 70°F (21°C)
Clearance	Valve guide clearance (exhaust)	.0030-.0050	in
Clearance	Valve guide clearance (intake)	.0015-.003	in
Clearance	Valve guide protrusion	11/32	in	from rocker box side of head
Clearance	Valve head to cylinder head face clearance	at least .030	in
Clearance	Valve seat width	3/64 to 1/16	in
Clearance	Valve spring length closed	1.528	in
Clearance	Valve stem tip-to-cap clearance	0.001 to 0.005	in
Gap	Anti-flicker breaker points gap	.025	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	Ambient	Capacity	Notes
Coolant	antifreeze				Replace annually in captive system
Engine oil	API CD/SE				Diesel engines; use CC/SE for first fill only (50 hours)
Engine oil	API SE or SE/CC				Gasoline engines
Engine oil	Multi-grade (such as 5W-30)	API classification CC/SE (grades 10W-30, 10W-40 or 5W-30 only)	below 0°C		Recommended for service in ambient temperatures of 32 F and colder
Engine oil	SAE 10W or 5W-20				0F to 30F
Engine oil	SAE 10W or 5W-30	API CD/SE or CD/SD			For 0F to 30F. Multigrade recommended at 30F and below
Engine oil	SAE 30	API CD/SE or CD/SD			For ambient above 30F. Use CC oil for first 50 hours break-in on new/rebuild
Engine oil	SAE 5W-20				Below 0F
Engine oil	SAE 5W-30	API CD/SE or CD/SD			For below 0F
Engine oil	See crankcase recommendation				Oil bath air cleaner (optional) uses the same grade of oil as the crankcase; SAE 50 oil used in compression blow-by test
Engine oil	same SAE number as is in the crankcase				Used in optional oil bath air cleaner cup; do not overfill
Engine oil	SAE 15W-40 or 20W-40		-10°C to 32°C		J-series water-cooled diesel engines
Fuel	ASTM 2-D or 1-D	min Cetane 45			Diesel; use 1-D below 32°F (0°C)
Fuel	ASTM 2-D or 1-D diesel fuel	min. Cetane number 45; low sulfur			Number 2 diesel gives best economy; below 32 F (0 C) use Number 1 diesel fuel. Pour point at least 10 F below lowest expected temperature
Fuel	No. 1 diesel				Use when ambient temperature below 32F, long periods of light load, or if preferred
Fuel	No. 2 diesel				Best economy
Fuel	Number 2 diesel fuel	Low sulfur content; pour point at least 10F below lowest expected temperature			Best economy; use Number 1 diesel fuel when ambient below 32F or during long periods of light load
Fuel	low sulfur content	pour point at least 10 degrees below lowest expected temperature			Keep fuel clean; leave room for expansion
Fuel	nonleaded gasoline				Recommended for gasoline engines
Grease	Powdered graphite (preferred) or non-gumming lubricating oil				For governor linkage ball joints; do not lubricate type with plastic socket
Grease	graphite lubricant				Steel governor ball joints
Other	Rust inhibitor (or SAE #10 oil)			1.0 oz	Pour 1 ounce of rust inhibitor into each cylinder for out-of-service protection

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 Carburetor adjustment

⚠ Do not force needles against seats.

Open both needles 1 to 1-1/2 turns off seats.
Apply full load; turn main fuel screw in until speed drops, then out to normal.
Remove load; turn idle screw out until speed drops, then in to normal.

Adjust Governor Linkage (Diesel) adjustment

Loosen locknuts on governor linkage, remove link at one ball joint.
Position governor arm and fuel control arm fully forward.
Adjust linkage so both ball joints fit without moving arms.
Tighten locknuts.
Release fuel solenoid plunger.

Adjust Injection Nozzle Opening Pressure adjustment

⚠ Do not adjust the pressure without a testing fixture

Tools: Static fuel nozzle testing fixture, Nozzle pressure tester

Remove each nozzle and remove the cap nut over the adjusting screw.
Install the nozzle on a static fuel nozzle testing fixture.
Adjust opening pressure to 1750 psi by turning the adjusting screw.
Clockwise increases pressure; counterclockwise decreases it.

Adjust Valve Clearance (Diesel) adjustment

Tools: feeler gauge, socket wrench

Turn flywheel to compression stroke for cylinder to adjust.
Turn flywheel clockwise additional 10 to 45 degrees.
Loosen locknut to increase clearance, tighten to reduce.
Use feeler gauge to set proper gap.
Adjust in firing order 1-2-4-3.

Adjust Valve Clearance (Four-Cylinder Engine) adjustment

⚠ Early model four-cylinder engines do not have a BC mark on the flywheel

Tools: Feeler gauge, Torque wrench

Adjust valve clearance in firing order 1-2-4-3 sequence.
Adjust number 1 cylinder, then turn flywheel clockwise 180 degrees for number 2.
Turn 180 degrees for number 4, then 180 degrees for number 3, adjusting each per steps.
Each position should be 10 to 45 degrees past the BC or TC flywheel mark as applicable.

Adjust Valve Clearance (Two-Cylinder Engine) adjustment

⚠ Adjust with engine at room temperature (approximately 75F); allow at least two hours cooling

Tools: Feeler gauge, Torque wrench

Turn flywheel until the cylinder is on its compression stroke.
Line up the TC mark on the flywheel with the timing pointer, then turn clockwise an additional 10 to 45 degrees.
Check the cylinder head bolt torque.
Using a feeler gauge, check clearance between rocker arm and valve; adjust with the lock nut.

Adjust Valve Tappet (Gasoline) adjustment

Tools: feeler gauge, wrench

Remove valve covers.
Crank engine until intake valve opens and closes.
Continue 1/4 turn until timing marks align.
Turn adjusting screw to obtain correct clearance.
Use flat feeler gauge between valve and valve rotator.

Adjust governor speed and sensitivity adjustment

Tools: Reed-type frequency meter, Mechanical tachometer

Turn governor speed adjusting nut clockwise to increase speed.
Turn counterclockwise to decrease speed.
Turn sensitivity adjusting ratchet nut counterclockwise to increase spring tension.
Adjust for maximum sensitivity without hunting.
Secure speed stud lock nut after adjusting.

Adjust the Vernatherm power element adjustment

Loosen the power element mounting screws.
Slide the assembly until it touches the roll pin with shutter closed.
Tighten the mounting screws.

Align brush rig to neutral position adjustment

Tools: Voltmeter

Remove end cover and band for access.
Start unit and apply full rated load.
Allow unit to reach full operating temperature.
Connect voltmeter across dc terminals.
Loosen brush rig mounting screws and rotate rig for highest voltage at full load.
Rotate rig one direction until voltmeter reading decreases; mark point.
Repeat in other direction; halfway between marks is neutral position.

Battery Charge Rate Adjustment adjustment

⚠ Avoid overcharging.

Tools: DC ammeter

Set slide tap on resistor R4 to about 2 amperes charging rate.
For frequent starts, increase charge rate slightly until battery stays charged.
Stop engine when readjusting to avoid shorts.

Decompression Release Adjustment adjustment

⚠ If screw is tightened more than one turn, exhaust valve could hit piston

Valves must be set for correct clearance first.
With piston 10 to 45 degrees past TDC on power stroke, hold arm in decompression position.
Turn set screw so it just touches exhaust rocker arm.
Turn screw exactly one revolution clockwise; lock with nut.
Release mechanism; check clearance; back off set screw if no clearance.

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
		12-lead broad range reconnectible alternator	12 lead	User connects for required voltage and amperage
		X1 to VR21-5	X1	for 50 Hertz
		X1 to VR21-6	X1	for 60 Hertz
110	1	518	V1	50 hertz
110/190	3	53C	V1	50 hertz
110/220	1	518	V1	50 hertz
110/220	1	53C	V1	50 hertz
110/220	3	518	V1	50 hertz
115	1	518	V2	50 hertz
115/200	3	53C	V2	50 hertz
115/230	1	518	V2	50 hertz
115/230	1	53C	V2	50 hertz
115/230	3	518	V2	50 hertz
120	1	2-wire		Reconnectible
120	1	3C	V1	60 hertz
120	1	518	V3	50 hertz
120-volt AC/32-volt DC	single	dual purpose plant		DJA wiring diagram dual purpose plant; diagram 6100220 page 60
120/208	3	3C	V1	60 hertz
120/208	3	53C	V3	50 hertz
120/208 volt	three	4 wire		DJA revolving armature; diagram 610C187 page 59
120/240	1	3-wire		Standard connection for MCCK/MDJE/MDJC/MDJF
120/240	1	3C	V1	60 hertz. Connect X1 to VR21-5 for 50 hertz and X1 to VR21-6 for 60 hertz generators. Jumper W10 on VR21 must connect VR21-V4 to V1, V2, or V3 as listed.
120/240	1	518	V3	50 hertz
120/240	1	53C	V3	50 hertz
120/240	3	3C	V1	60 hertz
120/240 volt	single	3 wire		DJA revolving armature; diagram 6100181 page 56
127/220	3	3C	V2	60 hertz
127/220	3	53C	V4	50 hertz
139/240	3	3C	V4	60 hertz
220/380	3	518	V1	50 hertz

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 DJB?

The Cummins/Onan DJB engine has an oil capacity of 3.0 liters.

What is the displacement of the Cummins/Onan DJB?

The Cummins/Onan DJB has a displacement of 1.04 liters with 2 cylinders.

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

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

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

A commonly reported issue on generators using the Cummins/Onan DJB is: Worn or sticking piston rings. Fix: Check compression. Clean or replace ring: a.