Home›Engines›Cummins/Onan MDJC

Cummins/Onan MDJC Engine

The Cummins/Onan MDJC is a 1.9 L natural engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the 12.0MDJC. It holds 6.2 L (1.6 gal) of oil and 4.3 L (1.1 gal) of coolant.

Also known as: Onan MDJC

1.9 L

Displacement

1800 rpm

Rated speed

6.2 L

Oil capacity

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

Engine specifications

Oil capacity	6.2 L
Coolant capacity	4.3 L
Displacement	1.9 L
Aspiration	natural
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan 12.0MDJC

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

Troubleshooting

Fault codes

Code	Meaning
e008	No specific name provided for e008
10	Overload

Symptoms & remedies

Symptom	Cause	Remedy
Engine does not crank.	Battery dead, loose connections, incorrect wiring, or faulty starter motor.	Check 12 VDC to ground at battery BT1 and at starter motor Bl. Check B+ present at TB11, K13, S1, and M11. Check battery cables for polarity and tightness at battery and starter motor. If battery is dead, check if centrifugal switch S1 is open to ground. Replace S4 or charge battery. Jumper battery cable connection to ground at starter. Check starter motor. With S11 at START, jumper K11 contacts to starter solenoid. Start relay K11 is defective; replace it.
Engine cranks but does not start.	Faulty switch or lead connections.	Check 12 VDC present between start terminal on S11 and ground (TB11-1) with S11 at START. Check 12 VDC present between M11-B+ and ground TB11-1 with S11 at START. Replace faulty switch S11 if necessary. Check lead from TB12-4 to fuel pump; check fuel pump and replace if necessary.
Engine starts but stops when start switch is released.	Faulty switch or lead connections.	Connect voltmeter from 12 VDC to ground at battery BT1 and at starter motor Bl. Check B+ present at TB11, K13, S1, and M11. Check battery cables for polarity and tightness at battery and starter motor. If battery is dead, check if centrifugal switch S1 is open to ground. Replace S4 or charge battery. Jumper battery cable connection to ground at starter. Check starter motor. With S11 at START, jumper K11 contacts to starter solenoid. Start relay K11 is defective; replace it.
No build up of AC output voltage.		Is Field Breaker CB21 on control panel ON? If not, step 2. Connect jumper wire across terminals of Field Breaker, CB21. Does AC output voltage build up? If yes, replace Field Breaker. If no, push to reset Field Breaker. Does AC output voltage build up? If yes but is high, low, unstable, or causes tripping of Field Breaker, refer to Tables B, C, or D. If no, step 4. Disconnect alternator stator leads 1 & 2 from TB21-1 and TB21-2 on VR22. Is reference voltage across 1 & 2 20 VAC or more? If not, refer to step 14.
AC output voltage builds up, but is unstable.		Are there any loose or broken wires or connections on voltage regulator assembly VR22? If yes, step 3. Is W9 (exciter field) wiring harness from VR22 to End bell OK? If no, replace PC Board VR21. Do not replace the printed circuit board until the trouble not on the PC board has been located and corrected to avoid damage to new PC board.
AC output voltage builds up, but is high or low.		Is set running at correct RPM? (See appropriate engine manual to set RPM) If no, step 3. Does adjustment of Voltage Adjusting knob for R22 on VR22 result in correct output voltage? If no, step 4. Does adjustment of potentiometer R26 on VR21 result in correct output voltage? If no, refer to step 5. Is correct voltage reference V4 to V1, V2, or V3 on VR21 being used? Refer to Figure 6. If no, replace voltage regulator PC board VR21. Do not replace the printed circuit board until the trouble not on the PC board has been located and corrected to avoid damage to new PC board.
AC output voltage builds up, but Field Breaker trips.		Does AC output voltage build up to 140% or more of rated voltage before Field Breaker trips? If yes, are there any loose or broken wires or connections on VR22? If no, is diode CR15 on VR21 OK? If no, are T21 windings and connections OK? If no, are generator stator leads properly connected? Refer to Figure 6. Replace VR21 if necessary. Are diodes CR1, CR2, CR3, CR4, CR5, CR6 in rotating rectifier assemblies OK? Check all diodes - more than one may be defective. Is brushless exciter stator winding OK? Is generator rotor field winding OK? If no, is brushless exciter rotor windings OK?

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

Repair guides

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

Service intervals

Item	Action	Hours	Months	Notes
Crankcase oil	Change	50 hr		First service — after first 50 hours of operation; drain while engine is still hot
Cylinder head bolts and valve clearance	Adjust	50 hr		First service — after first 50 hours on an overhauled engine
Water filter	Check	100 hr		check after every 100 hours; change sooner in dirty water
Oil filter	Replace	200 hr		every 200 hours of normal operation
Crankcase breather pipe	Clean	500 hr		MDJC, MDJF Begin Spec T
Valve stem tip-to-cap clearance	Check	5000 hr		or whenever parts exposed or removed
Cooling system	Clean		12 mo	clean and flush at least once a year
Heat exchanger sea water side	Clean		12 mo	yearly; remove end caps and flush tubes
Zinc pencils	Inspect		2 mo	replace if less than half original size

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 end play	0.007-0.039	in	room temperature
Clearance	Center main bearing clearance (4 cylinder)	0.0024-0.0052	in	original
Clearance	Connecting rod bearing clearance	0.001-0.003	in
Clearance	Crankshaft end play	0.010-0.015	in	room temperature
Clearance	Main bearing clearance (1 & 2 cylinder)	0.0014-0.0052	in	replacement
Clearance	Main bearing clearance (1 & 2 cylinder)	0.002-0.0033	in	original
Clearance	Piston clearance in cylinder	0.005-0.007	in	90 degrees to pin, below oil ring
Clearance	Ring gap	0.010-0.020	in
Clearance	Valve guide clearance exhaust	0.0030-0.0050	in
Clearance	Valve guide clearance intake	0.0015-0.003	in
Clearance	Valve stem tip-to-cap clearance	0.001-0.005	in
Gap	Centrifugal switch gap	0.020	in
Pressure	Compression pressure	300-350	psi	cranking at about 300 rpm, prior to Spec P
Pressure	Compression pressure	350-400	psi	cranking at about 300 rpm, Spec P and later
Pressure	Delivery valve line pressure	300-600	psi	engine running
Pressure	Fuel transfer pump pressure	12-14	psi	operating at 1800 rpm
Pressure	Fuel transfer pump pressure	5-6	psi	operating at 1800 rpm
Pressure	Injection nozzle opening pressure	1900-1950	psi	new
Pressure	Injection nozzle opening pressure	2100-2200	psi	new Bryce/Kiki
Pressure	Low oil pressure switch close	13-15	psi	increasing pressure
Pressure	Oil pressure	25	psi	normal at operating temperature
Pressure	Oil pressure minimum	20	psi	governed speed; inspect if below
Torque	Adapter and pump mounting screws	20-24	ft-lb
Torque	Center main bolt (4 cylinder)	97-102	ft-lb
Torque	Connecting rod bolt	27-29	ft-lb
Torque	Cylinder head bolt	44-46	ft-lb
Torque	Delivery valve holder torque (Bryce)	29-33	ft-lb
Torque	Delivery valve holder torque (Kiki)	44-47	ft-lb
Torque	Exhaust manifold nuts	13-15	ft-lb	tighten evenly
Torque	Flywheel mounting screw	65-70	ft-lb
Torque	Fuel inlet stud	15-18	ft-lb
Torque	Fuel pump mounting screws	15-20	ft-lb
Torque	Gear case cover	18-20	ft-lb
Torque	Glow plug	10-15	ft-lb
Torque	High pressure line nuts	16-18	ft-lb
Torque	Injection nozzle mounting screws	20-21	ft-lb
Torque	Injection pump mounting screws	15-16	ft-lb
Torque	Injection pump mounting screws (PSU)	18-21	ft-lb
Torque	Intake manifold	13-15	ft-lb
Torque	Nozzle cap nut	50-55	ft-lb
Torque	Nozzle flange capscrews	20-21	ft-lb
Torque	Oil base mounting screws	45-50	ft-lb
Torque	Oil filter	hand tight plus 1/4 to 1/2 turn
Torque	Oil pump mounting screws	15-20	ft-lb
Torque	Rear bearing plate	40-45	ft-lb
Torque	Rocker arm nut	4-10	ft-lb	friction only; use to adjust valve lash
Torque	Rocker arm stud	35-40	ft-lb
Torque	Rocker-box cover	8-10	ft-lb
Torque	Water pump cover screws	15-17	inch-lb
Valve clearance	Exhaust valve clearance	0.010	in	cold, MDJA Begin Spec D
Valve clearance	Exhaust valve clearance	0.013	in	cold
Valve clearance	Exhaust valve clearance	0.016	in	cold
Valve clearance	Exhaust valve clearance	0.017	in	cold
Valve clearance	Exhaust valve clearance	0.020	in	cold, MDJA Spec A-C
Valve clearance	Intake valve clearance	0.010	in	cold, MDJA Begin Spec D
Valve clearance	Intake valve clearance	0.011	in	cold
Valve clearance	Intake valve clearance	0.015	in	cold
Valve clearance	Intake valve clearance	0.017	in	cold
Valve clearance	Intake valve clearance	0.020	in	cold, MDJA Spec A-C

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	Notes
Coolant	50/50 mixture antifreeze and clean water			increase antifreeze percentage in extremely low temperatures (-25F or lower)
Engine oil	5W-30	API CC/SE	below 0°C	recommended for service in ambient temperatures of 32F and colder
Engine oil	SAE 15W-40 or 20W-40	API CD/SE or CC/SE	-10°C to 32°C	SAE 15W-40 or 20W-40 in 15F (-10C) through 90F (32C); multi-grade 5W-30 below 32F (0C)
Fuel	ASTM 2-D or 1-D	minimum Cetane number 45		use 1-D below 32F, long periods of light load or no load; low sulfur; pour point at least 10F below lowest expected

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

Procedures

Fuel Injection Pump Timing (MDJA Method 2) adjustment

Install pump with 0.006-inch (0.15 mm) shims.
Loosen delivery valve holder to relieve spring pressure.
Rotate flywheel to about 15 degrees before port closing point.
Blow in pump inlet and rotate flywheel slowly clockwise until air stops.
Measure distance from port closing point to PC mark.
Select shims from table and install pump.

Valve Clearance Adjustment (2-Cylinder) adjustment

Tools: feeler gauge

Turn flywheel until cylinder to be adjusted is on compression stroke.
Align TC mark with timing pointer.
Turn flywheel clockwise an additional 10 to 45 degrees.
Check clearance between rocker arm and valve with feeler gauge.
Adjust with lock nut securing rocker arm to cylinder head.

Valve Clearance Adjustment (4-Cylinder) adjustment

Tools: feeler gauge

Adjust valves in firing order 1-2-4-3.
Adjust number 1 cylinder as for 2-cylinder engine.
Turn flywheel 180 degrees clockwise for number 2 cylinder.
Adjust number 2 cylinder.
Turn flywheel 180 degrees clockwise for number 4 cylinder.
Adjust number 4 cylinder.
Turn flywheel 180 degrees clockwise for number 3 cylinder.
Adjust number 3 cylinder.

Compression Test diagnostic

Tools: compression gauge

Run engine until thoroughly warm.
Stop engine and remove all injection nozzles.
Insert compression gauge in one nozzle hole.
Crank engine and note reading.
Squirt SAE 50 oil into cylinder and repeat check.
Increase in compression indicates piston blow-by.

Bleeding Fuel System maintenance

Disconnect fuel return line.
Operate hand priming lever until fuel flows free of air bubbles.
Reconnect fuel return line.
If camshaft pump lobe is up, crank engine one revolution.
Return priming lever inward to disengaged position.

Draining Cooling System maintenance

⚠ Do not bleed hot, pressurized coolant from a closed cooling system.

Remove engine block drain plug on left front side.
Remove water pump drain plug or loosen pump cover.
Remove plug from underside of exhaust manifold.
Remove plug from front side of expansion tank.
Drain heat exchanger and tank heater.
Replace and tighten all plugs, fittings, and clamps.

Filling Heat Exchanger maintenance

Remove fill cap.
Open fill vent valve.
Fill with coolant until vents begin to overflow.
Close fill vent valve.
Replace fill cap.
Operate unit 10 minutes at full load; watch for leaks.
Shut down and check water level.
Fill system to top with coolant.

Oil Filter Change maintenance

⚠ Hot crankcase oil can cause burns.

Place pan under old filter and remove by turning counterclockwise.
Clean filter mounting area.
Lubricate gasket on new filter with oil.
Screw filter on clockwise until gasket touches mounting base.
Tighten 1/2 turn.

Preheating and Starting operation

⚠ Do not use ether as a starting aid.

Engage PREHEAT 30 seconds above 55F (13C) or 60 seconds below 55F.
Engage START while continuing preheat.
Hold until engine comes up to speed.
If engine fails to start in 15-20 seconds, repeat steps 1 and 2.
Never preheat more than 60 seconds.

Stopping operation

Push fuel solenoid switch to Stop position.
Release switch when set stops.
If stop circuit fails, close fuel valve.

Water Pump #131-0152 Disassembly repair

Tools: pliers, screwdriver

Remove pump end plate screws, end plate, and gasket.
Pull out neoprene impeller with pliers.
Disconnect hoses and remove cap screws holding pump.
Loosen set screw and tap to free cam.
Lift out cam and wear plate.
Remove retaining ring and slide seat assembly off shaft.
Pry bellows assembly out through drain slots.
Drive shaft and bearing assembly out.

Water Pump #132-0110 Disassembly repair

Remove water inlet fitting, drive belt pulley, cover screws, and pump cover gasket.
Unscrew threaded impeller from pump shaft counterclockwise.
Slide seal seat, wear face, and bellows assembly off shaft.
Loosen clamp screw and slide pump body off pedestal.
Remove bearing lock ring and drive shaft and bearing assembly out of pedestal.

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 MDJC?

The Cummins/Onan MDJC engine has an oil capacity of 6.2 liters.

What is the displacement of the Cummins/Onan MDJC?

The Cummins/Onan MDJC has a displacement of 1.9 liters.

Which generators use the Cummins/Onan MDJC engine?

The Cummins/Onan MDJC powers 1 generator set(s), including Cummins/Onan 12.0MDJC.