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Kubota D722B Engine

Name: Kubota D722B Engine
Brand: Kubota

The Kubota D722B is a 719 L 3-cylinder engine rated at 3600 rpm. It powers generator sets from Cummins/Onan, including the 7.5 MDKWB, 9.0 MDKWB and MDKWB. It holds 4.73 L (1.2 gal) of oil and 3.5 L (0.9 gal) of coolant.

Also known as: Kubota D722B

719.0 L

Displacement

Cylinders

3600 rpm

Rated speed

4.73 L

Oil capacity

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

Engine specifications

Oil capacity	4.73 L
Coolant capacity	3.5 L
Displacement	719.0 L
Cylinders	3
Rated speed	3600 rpm

Generator sets powered by this engine

Cummins/Onan 7.5 MDKWB Cummins/Onan 9.0 MDKWB Cummins/Onan MDKWB

How to read your Kubota engine serial & model number →

Common problems

Weakness and Sleepiness
Fix: 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
Fix: 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
Fix: 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
Fix: 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.
Dizziness
Fix: 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.
UNSTABLE OUTPUT VOLTAGE, ENGINE SPEED STABLE
Cause: Broken wires or loose connections on voltage regulator assembly, brushes not OK
Fix: Check wiring harness from regulator assembly to end bell, repair as required, inspect brushes, repair wiring or replace as required, replace the voltage regulator
UNBALANCED GENERATOR OUTPUT VOLTAGE
Cause: Load at generator terminals not removed, unbalanced output voltage still present
Fix: Remove load at generator terminals
OUTPUT VOLTAGE TOO HIGH OR TOO LOW
Cause: Set AC output overloaded
Fix: Remove part of the set load
NO AC OUTPUT VOLTAGE AT RATED ENGINE RPM
Cause: Load circuit breakers closed, circuit open between brush block and voltage regulator, brushes stuck in holder or not making good contact with slip rings, opens or grounds in rotor, stator, incorrect field voltage, incorrect F1 and F2 leads installed on terminals
Fix: Locate cause of overload and correct as required, reset breaker or replace if bad, check continuity of circuit breakers and replace if necessary, check for open circuit between brush block and voltage regulator, release brushes if jammed in holder, clean slip rings if dirty, test continuity of rotor, stator, replace component if defective, test field voltage, check voltage regulator, examine brush block connections, connect brush leads to correct terminals
Low Oil Pressure
Cause: Oil level is low.
Fix: Add oil to bring the level up to full mark. Inspect engine exterior for leaks and repair as necessary.
Is engine getting fuel? Exhaust smoke should be blue-white and fuel flow steady from fuel return line.
Cause: Incorrect fuel? See Operator’s Manual recommendations.
Fix: Check fuel system: test fuel pump per Checkout [H], test fuel tank level, shut-off valves, fuel lines and connections, fuel filters, and injection pump. Okay? Does K12 fuel solenoid energize when S10(S12) is in Start position? Check B+ circuit through S10(S12). Test S11 per Checkout [G]. Test K12 per Checkout [F]. Check switch S10(S12) per Checkout [G]. Check heater relay per Checkout [E]. Check heater wiring.
Is battery dead?
Fix: Check CB8 circuit breaker. If okay, jumper battery cable B+ connection to K9 starter so-lenoid terminal. Does engine crank? With S10(S12) in Start position, is battery voltage present between K9 terminal S and ground? If K9 does not energize, test per Checkout [D] and replace if bad. Is battery voltage present at K9 solenoid terminal with S10(S12) in Start position? Check battery per Checkout [A] and recharge or replace. Check battery charger operation per Checkout [C]. Check battery cables for clean tight connections (ref. Checkout [B]). Check K9 starter so-lenoid and motor: if bad, repair or replace. Check B+ wiring to S10(S12), and between S10(S12) and K9. Check NC contacts of K16 per Checkout [E]. Replace if bad.
High Exhaust Temperature
Fix: The high exhaust temperature switch closes on temperature rise above 230° F (110° C). It closes to shut down the set if raw water flow is lost. It opens again when the temperature reaches about 190° F (88° C).
High Coolant Temperature
Fix: Check coolant level in the exhaust manifold after allowing the engine to cool down. Ensure pump belt is OK and has proper tension. The raw water flow at the exhaust outlet should be about 3 gal./min. (11.4 liter/min.). Also check cooling system cleanliness.
Has control circuit breaker CB8 opened?
Fix: Check B+ wiring for shorts to ground causing excessive current draw. If none, check control circuit breaker CB8 for improper wiring. Check fuel solenoid adjustment. Does set stop when start switch is released? Does run relay K13 energize and contacts close when generator set comes up to operating speed? Check NC contacts of K15 shutdown relay. Check diode CR12. Check for AC voltage build-up during cranking. Check engine monitors for proper operation and wiring. See engine troubleshooting data in engine service manual.

Compiled from service & troubleshooting documentation across every generator set that uses the Kubota D722B.

Service intervals

Item	Action	Hours	Months	Notes
Coolant level	Check	8 hr		Daily or after 8 hours.
Engine oil level	Check	8 hr		Daily or after 8 hours.
Exhaust system	Inspect	8 hr		Every startup and after every eight hours of operation
Fuel level	Check	8 hr		Daily or after 8 hours.
Oil level	Check	8 hr		Daily or after 8 hours.
Set	Inspect	8 hr		Daily or after 8 hours. Check for oil, fuel, cooling and exhaust system leaks; check exhaust audibly and visually with genset running.
generator set	Inspect	8 hr		Daily/8hr: general inspection for oil, fuel, coolant, or exhaust leaks; visual/audible check of exhaust system while running
Crankcase oil	Drain	35 hr		First service — Perform after first 35 hours of operation on new genset
Battery specific gravity	Check	100 hr	1 mo	Monthly or after 100 hours.
Water/sediment from fuel filter	Drain	100 hr	1 mo	Monthly or after 100 hours.
pump belt tension	Check	100 hr	1 mo	visually check for slipping
crankcase oil and filter	Change	250 hr	6 mo	First service — first service at 35 hours on new unit; more often in dusty conditions; annually if used less than 250 hours
Fuel filter	Change	500 hr	12 mo	Yearly or after 500 hours.
Generator assembly	Clean	500 hr	12 mo	Clean when dust and dirt accumulate.
Genset brushes	Check	500 hr	12 mo	To be performed by authorized service technician.
cooling system	Clean	500 hr	12 mo	flush and clean cooling circuit
fuel filter	Replace	500 hr	12 mo
generator	Clean	500 hr	12 mo
generator brushes	Check	500 hr	12 mo	to be performed by an authorized service technician
Generator bearing	Inspect	1000 hr		Check for evidence of outer case rotation
Coolant	Change		12 mo
Coolant pressure cap	Replace		24 mo	For optimum performance
Fuel filter water/sediment	Drain	100 hr	1 mo	Monthly
Generator bearing	Replace		60 mo	Bearing grease gradually deteriorates due to oxidation
Generator brushes	Inspect		6 mo	Inspect for wear and cleaning

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
Other	Battery charge alternator maximum output	10	amperes	regulated
Other	Battery charge alternator maximum output (regulated)	10	amperes
Other	Battery cranking performance at 0° F (-18° C)	360	ampere	minimum
Other	Battery electrolyte specific gravity	1.260	at 80°F (27°C)	charge if less than 1.215
Other	Battery electrolyte specific gravity (charge if below)	1.215
Other	Battery minimum cranking performance	360	ampere	@ 0°F (-18°C)
Other	Battery specific gravity (charge if less than)	1.215
Other	Battery specific gravity at full charge	1.260	at 80°F (27°C)	stop charging when reached
Other	Bore and stroke	67 x 68	mm (2.64 x 2.68 inches)
Other	Coolant mixture	50-50	ethylene glycol and distilled water
Other	DC control breaker	15	ampere
Other	Exhaust hose vertical rise	48	inches (1.2 m)	maximum
Other	Exhaust line downgrade	1/2	inch per linear foot (42 mm/m)	minimum
Other	Frequency adjustment stop point (50 to 60 Hz conversion)	63	Hz	no load, low-speed adjustment screw turned in
Other	Frequency adjustment stop point (60 to 50 Hz conversion)	53	Hz	no load, low-speed adjustment screw turned out
Other	Frequency regulation	5	percent	no load-rated load
Other	Frequency regulation, no load-rated load	5	percent
Other	Fuel inlet/return fitting	1/8-27 NPT Female
Other	Fuel pump lift (self-priming)	1.2	meters (48 inches)
Other	Preheat time above 86°F (30°C)	10	seconds	above 86°F (30°C)
Other	Preheat time below 32°F (0°C)	30	seconds	below 32°F (0°C)
Other	Preheat time between 32° to 50°F (0° to 10°C)	20	seconds	between 32° and 50°F
Other	Preheat time between 50° to 86°F (10° to 30°C)	15	seconds	between 50° and 86°F
Other	Pump belt tension	22	pounds (10 kg) deflects 0.4 inch (10 mm)	finger pressure at middle of belt
Other	Pump belt tension	22 pounds (10 kg) finger pressure; deflection 0.4 inch (10 mm)		at middle of belt
Other	Raw water flow at exhaust outlet	3	gal/min (11.4 liter/min)
Other	Total air per minute required (cooling and combustion)	4.25	m3/min. (150 ft3/min.)
Other	Total air required (cooling and combustion)	4.25	m3/min (150 ft3/min)
Other	Total displacement	479	cc (29.23 cubic inches)
Other	Total displacement	719	cc (43.89 cubic inches)
Other	Voltage regulation, no load-rated load	+/-2	percent
Other	Voltage regulation, no load-rated load	±2	percent
Pressure	Coolant pressure cap rating	7	psi	(48 kPa)
Pressure	Cooling system pressure cap rating	7	psi (48 kPa)
Pressure	Engine oil pressure	28 to 64	psi (294 to 543 kPa)	engine at operating temperature
Pressure	Exhaust back pressure	3.0	inches of mercury (76 mm Hg; 10 kPa)	maximum
Pressure	Fuel pump output pressure	3.5 to 6	psi (24-41 kPa)	start position, static test
Pressure	Low oil pressure switch S15	10	psi (170.3 kPa)	closes, deactivates shutdown relay and stops engine
Pressure	Maximum back pressure at injector fuel return line fitting	15	psi (103 kPa)	maximum
Pressure	Oil pressure	28 to 64	psi (294 to 543 kPa)	engine at operating temperature
Pressure	Oil pressure at operating temperature	28 to 64	psi (294-543 kPa)	engine at operating temperature
Pressure	Oil pressure switch actuation	9	psi (62 kPa)	fault circuit actuates if pressure drops below
Resistance	Rotor field resistance (F1-F2)	22.1	ohms ± 10%
Resistance	Rotor field resistance (F1-F2)	27.6	ohms ± 10%
Resistance	Rotor/stator insulation resistance (grounds test)	100,000	ohms (minimum, or questionable)	megger or insulation resistance meter, 500 VDC
Resistance	Stator winding resistance Q1-Q2	1.88	ohms ± 5%
Resistance	Stator winding resistance Q1-Q2	2.238	ohms ± 5%
Resistance	Stator winding resistance T1-T2	0.186	ohms ± 5%
Resistance	Stator winding resistance T1-T2	0.371	ohms ± 5%
Resistance	Stator winding resistance T3-T4	0.186	ohms ± 5%
Resistance	Stator winding resistance T3-T4	0.371	ohms ± 5%
Speed	Engine speed	3000	rpm	50 Hz sets
Speed	Engine speed	3600	rpm	60 Hz sets
Speed	Engine speed 50 Hz sets	3000	rpm
Speed	Engine speed 60 Hz sets	3600	rpm
Temperature	Coolant temperature	165 to 195	°F (74 to 91 °C)	depending on load and ambient temperature
Temperature	Coolant thermostat switch	222	F	closes at (106 C)
Temperature	Coolant thermostat switch closes	222	°F (106 °C)
Temperature	High engine (coolant) temperature switch S17	222	°F (105.6°C)	closes, activates shutdown
Temperature	High exhaust temperature shutdown switch closes	221 to 239	°F (105 to 115 °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	Capacity	Notes
Coolant	50-50 mixture of ethylene glycol and distilled water	Fleetguard ES Compleat/EG Premix			MDKUB 2 L, MDKWB 3.5 L
Coolant	50/50 ethylene glycol antifreeze and clean water, with rust inhibitor, no stop-leak				Fill recovery tank half way between high and low marks
Coolant	50/50 mixture of ethylene glycol anti-freeze and water	contains rust and corrosion inhibitor; no stop-leak additive	above -37°C	2.0 liters	Freeze protection to -34°F (-37°C).
Coolant	50/50 ethylene glycol/water		above -34°C		Freeze protection to -34°F (-37°C). MDKUB capacity 2 liters (2.1 qt); MDKWB 3.5 liters (3.7 qt). Use reliable brand with rust/corrosion inhibitor; no stop-leak additive.
Engine oil	15W40	Premium Blue E			Lubrication oil; MDKUB 3.78 L, MDKWB 4.73 L
Engine oil	API Class CD or better (CD, CE); SAE viscosity grade per ambient temperature			3.78 liters	Use same brand when adding oil; do not overfill.
Engine oil	API SF/CD	API SF/CD			MDKUB capacity with filter 3.78 liters (4 quarts); MDKWB 4.73 liters (5 quarts). Select viscosity per Table 1. Do not use synthetic or non-detergent oil.
Engine oil	SAE viscosity grade per oil viscosity vs. temperature chart	API Class CD or better (CD, CE)			Oil capacity with filter: MDKUB 3.78 liters (4 quarts); MDKWB 4.73 liters (5 quarts). Lubrication oil Premium Blue E 15W40 referenced.
Fuel	ASTM 2-D (Diesel No. 2) or ASTM 1-D (Diesel No. 1), minimum cetane number 45	ASTM			Use No. 1 diesel below 32°F (0°C) and for extended light-load operation
Fuel	ASTM 2-D (No. 2 Diesel) or ASTM 1-D (No. 1 Diesel)	Minimum Cetane number 45; low sulfur content fuel with cloud point at least 10 degrees below lowest expected fuel temperature	below 0°C		Use No. 1 diesel when ambient temperatures are below 32 F (0 C) and during long periods of light engine load.
Fuel	ASTM 2-D (No. 2 Diesel) or ASTM 1-D (No. 1 Diesel); minimum Cetane number 45	low sulfur content; cloud point at least 10 degrees below lowest expected fuel temperature			Use No. 1 diesel when ambient below 32°F (0°C) and during long periods of light load.
Fuel	No. 2 diesel				Gas oil (Red Diesel, Fuel Oil type A1 or A2)

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

Fault codes

Code	Name	Meaning	Severity	Action
1	High engine coolant temperature	One blink indicates shutdown due to high engine coolant temperature	Shutdown	Check coolant level, pump belt tension, raw water flow and cooling system cleanliness
2	Loss of engine oil pressure	Two blinks indicate shutdown due to a loss of engine oil pressure	Shutdown	Check oil level, add oil if low, inspect for leaks
3	Service fault	Three blinks indicate a service fault. Press Stop once to cause the two-digit, second-level shutdown code to blink. The first set of blinks represents the tens digit and the second set the units digit	Shutdown	Press Stop once to read the two-digit second-level code; contact an Onan dealer or distributor
4	Cranking time exceeded	Four blinks indicate that cranking time exceeded 35 seconds	Shutdown	Check the fuel supply and make sure the fuel system has been primed

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 Output Voltage (Faceplate) adjustment

⚠ High voltages within the control cabinet can cause severe personal injury or death.

Tools: voltmeter

Connect a voltmeter to the set output.
Power the set.
Loosen the lock nut and set the faceplate voltage adjustment trim pot to mid range.
Lock the pot into position by tightening the lock nut.

Changing Genset Frequency (50/60 Hz) adjustment

⚠ Disconnect starting battery positive terminal first to disable the genset before adjustments

Tools: Digital volt-ohmmeter, Frequency meter

Turn the generator set off and open the control box
Move the 60 Hz/50 Hz switch on the regulator board to the desired value
Remove all load and connect a frequency meter across the output
Loosen and back off the lock nuts on the speed adjustment screws
Turn the set on with no load and adjust low/high speed screws per conversion direction
Tighten lock nuts once target frequency is reached (53 Hz or 63 Hz stop points)
Center the voltage adjustment pot and adjust output voltage to rated value ± 5 VAC
Fine tune output voltage with the faceplate pot and recheck

Pump Belt Adjustment adjustment

⚠ Do not operate genset without belt guard in place.

⚠ Too much tension may reduce pump belt life.

Tools: finger pressure

Disconnect battery cables, negative first, and remove housing and belt guard.
Loosen bottom pivot bolt on alternator.
Loosen bolt through long slot in alternator mounting bracket.
Slide alternator until tension is right.
Belt tension is correct when 22 pounds (10 kg) finger pressure at middle of belt deflects it about 0.4 inch (10 mm).

Voltage Adjustment adjustment

⚠ Contact with high voltage can cause severe injury or death; use insulated tools and stand on a dry mat

Tools: Voltmeter, Flat-blade screwdriver

Attach a voltmeter securely to the L1 and L2 leads
Start the generator set and place a typical load on its output
Loosen the hex locking nut and adjust the faceplate voltage pot to correct voltage (117 VAC at 60-61 Hz for most 60 Hz applications)
If needed, center faceplate pot and adjust with the regulator board pot, then fine tune at the faceplate

Fuel Pump Test diagnostic

Tools: 0-15 psi pressure gauge

Disconnect fuel line at pump outlet and connect a 0-15 psi pressure gauge
Push Start/Stop switch to START and hold until pressure stabilizes (3.5-6 psi)
Repeat the test with the engine running
If pressure is below 3.5 psi, check for restrictions or relocate pump closer to tank; replace if defective

Test Fuel System diagnostic

⚠ Fuel leakage in boats presents fire and explosion hazards that can result in severe personal injury or death.

After installation, test the fuel system for tightness per USCG specification 33CFR183.542.
Any leak must be found and corrected before putting the fuel system into service.

Voltage Regulator Test diagnostic

⚠ Do not touch electrical wiring or components during testing

Tools: Volt-ohmmeter (diode check mode)

Stop the generator set and disconnect starting battery, negative lead first
Unscrew the voltage regulator from the control box
Disconnect the voltage regulator from the wiring harness
Set the volt-ohmmeter to diode check
Test terminal pairs per Table 6-1 and compare readings to good/bad values

Install Coolant Recovery Tank installation

Use the bracket as a template to locate mounting holes.
Allow a minimum of 2 inches (51 mm) from the top of the tank to any upper structure.
Mount with two 5/16 inch (8mm) bolts.
Use a length of hose from the kit between the radiator overflow and the dip-tube connector on the recovery tank.
Allow sufficient hose lengths so the tank can be easily removed from the bracket to add coolant.

Mount Generator Set installation

Tools: drill

Remove the carriage bolts, nuts and washers from the drip tray.
Drill holes in the floor or deck in the positions indicated.
Use 3/8” bolts or the nearest metric equivalent to mount the generator set.

Mount Remote Start-Stop-Preheat Panel installation

⚠ The electrical code does not allow the remote-control harness or wiring to be routed in the same conduit with AC wiring.

⚠ Be sure to seal all openings made for the wiring so exhaust or fuel vapors cannot enter the living quarters.

Tools: screwdriver

Unscrew the two hold-down screws that hold the panel in place.
Remove and discard the short 6” wiring harness connecting control panel P1 to genset J1.
Disconnect the leads that connect the running time meter to the terminal block inside the control box.
Replace the short harness with a longer harness that will reach the control panel mounting location.
Route the harness through the opening at the side of the control box.
Use the blank panel provided with the set to cover the space where the removable control panel had been.

Battery Care maintenance

⚠ Batteries present explosion hazard.

⚠ Battery electrolyte can cause severe eye damage and burns.

Tools: battery hydrometer, terminal puller tool

Keep battery case clean and dry.
Make certain cable connections are clean and tight; remove corrosion with ammonia solution or baking soda solution.
Identify positive and negative cables before making connections; connect negative cable last.
Maintain electrolyte level by adding distilled water to split-level marker in each cell.
Check specific gravity with hydrometer; charge if less than 1.215; stop charging at 1.260 at approximately 80°F (27°C).

Break-in procedure maintenance

⚠ Carbon deposits from prolonged no-load running can clog injectors, glaze cylinder walls, and stick piston rings and valves

Drain crankcase oil after the first 35 hours of operation
Minimize unloaded running time during break-in; connect an electrical load if extended running is required

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

Aftermarket parts that fit this engine

16871-03310 FridayParts $21.00 16851-15110 FridayParts $56.47 17549-51012 FridayParts $401.49 2500Rpm FridayParts $4999.99 10.2KW FridayParts $799.99 14601-14410 FridayParts $43.82 3-Year FridayParts $11.99 14Pcs FridayParts $68.90 14601-03450 FridayParts $60.00 14601-03452 FridayParts $60.00 14601-03453 FridayParts $60.00 1J080-03450 FridayParts $60.00 16271-63012 FridayParts $132.73 15741-63010 FridayParts $103.95 WC20B FridayParts $522.00

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.

Also used in

Bobcat 320 — Excavator
Bobcat 322 — Excavator
Bobcat 453 — Skid Steer Loader
Bomag BW80AD-2 — Compactor
Bomag BW80ADH-2 — Compactor
Kubota B7400HSD — Tractor
Kubota G1900 — Lawn Equipment
Kubota G1900S — Lawn Equipment
Kubota K008-5 — Excavator Compact
Kubota U10-3 — Excavator
Volvo Construction Equipment DD14S — Compactor
Volvo Construction Equipment DD16 — Compactor

Other equipment known to use this engine, via filter-application cross-reference — useful for sourcing parts even when your exact machine isn't listed elsewhere on this page.

Common questions

What is the oil capacity of the Kubota D722B?

The Kubota D722B engine has an oil capacity of 4.73 liters.

What is the displacement of the Kubota D722B?

The Kubota D722B has a displacement of 719.0 liters with 3 cylinders.

Which generators use the Kubota D722B engine?

The Kubota D722B powers 3 generator set(s), including Cummins/Onan 7.5 MDKWB, Cummins/Onan 9.0 MDKWB, Cummins/Onan MDKWB.

What is a common problem with the Kubota D722B engine?

A commonly reported issue on generators using the Kubota D722B is: Weakness and Sleepiness. Fix: 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..