Home›Engines›Cummins/Onan L634D

Cummins/Onan L634D Engine

The Cummins/Onan L634D is a 6-cylinder naturally aspirated engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the DL6. It holds 8.5 L (2.2 gal) of oil and 16.8 L (4.4 gal) of coolant.

Also known as: Onan L634D

Cylinders

1800 rpm

Rated speed

8.5 L

Oil capacity

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

Engine specifications

Oil capacity	8.5 L
Coolant capacity	16.8 L
Cylinders	6
Aspiration	naturally aspirated
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan DL6

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

Common problems

Engine does not crank
Cause: Battery dead; start solenoid K1 does not energize; less than 7 volts DC between K1 terminal S and ground; less than 7 volts DC between B1 starter solenoid terminal and ground; K1 fault relay not energized; faulty battery cables or connections; faulty B1 starter solenoid or motor; faulty K1 start solenoid, K2 on/off relay, K3 and K11 start-disconnect relays, S10 switch, or connections
Fix: Check battery per Checkout [A] and recharge or replace; check alternator operation per Checkout [C]; check K1 start solenoid, K2 on/off relay, K3 and K11 start-disconnect relays, S10 switch, and all connections per Checkouts D, E, and G; check wiring and connections between K1 terminal I and the solenoid terminal B1; check for possible fault conditions and, if ok, check K1 fault relay per Checkout E; check battery cables for clean and tight connections per Checkout [B]; check B1 starter solenoid and motor and repair or replace if bad; jumper battery cable B+ connection to B1 starter solenoid terminal and check whether engine cranks
Engine cranks but does not start
Cause: K3 fuel solenoid does not energize when S10 is in Start position; preheat system not operating properly; no fuel from fuel supply system (fuel tank, shutoff valves, fuel lines and connections, fuel filters, transfer pump); fault condition indicated by panel light (S1 engine temp. switch, S6 overspeed switch, S3 oil pressure switch, K1 fault relay short to ground); battery voltage not read between stop terminal of S10 and ground as RPM increases; incorrect fuel; K2 on/off relay faulty
Fix: Check K3 fuel solenoid (Test F) and related wiring; check heater solenoid K2 and switch S11 per Checkouts [D] and [G]; check wiring and heater elements; check fuel supply system: fuel tank, shutoff valves, fuel lines and connections, fuel filters and transfer pump; check for possible fault condition and, if OK, check S1 engine temp. switch, S6 overspeed switch, and S3 oil pressure switch, and check K1 fault relay for short to ground; check switch S10 and related wiring for open circuit or short to ground; use correct fuel per Operator's Manual recommendations; jump normally open contacts of K2 on/off relay and check whether engine starts and runs; replace all engine monitor circuit board
Engine will not crank
Cause: Indicates possible fault with control or starting system; fault lamp on
Fix: Correct fault and reset control
Engine starts but stops after running several seconds
Cause: K2 on/off relay faulty
Fix: Replace K2 on/off relay
Unstable output voltage, engine speed stable at rated r/min
Fix: Refer to Flow Chart B for troubleshooting procedures
Unstable output voltage, engine speed stable 1800 RPM
Fix: Refer to Flow Chart B for the troubleshooting procedures
Unbalanced generator output voltage
Fix: Refer to Flow Chart E for the troubleshooting procedures
SWITCH OFF lamp flashes
Cause: Indicates Start/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used
Fix: Move the Start/Stop/Remote switch to the Remote position for automatic starting
PRELO OIL PRES lamp lights. Engine continues to operate
Cause: Indicates engine oil pressure has dropped to 20 psi (138 kPa)
Fix: If engine can be stopped, follow procedures in step 5; if generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure
PRE HI ENG TEMP lamp lights. Engine continues to operate
Cause: Indicates engine has begun to overheat and engine temperature has risen to approximately 215°F (102°C)
Fix: If engine can be stopped, follow procedures in step 3; if generator is powering critical loads and cannot be shutdown: check air inlets and outlets and remove any obstructions to airflow; open doors or windows in generator area to increase ventilation; reduce load if possible by turning off non-critical loads
OVERCRANK lamp lights and engine stops cranking after 45 to 75 seconds
Cause: Indicates possible fuel system problem
Fix: When the engine has cooled, make the following checks: check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required; check for dirty fuel filter and replace if necessary (see MAINTENANCE section); check for dirty or plugged air filter and replace if necessary (see MAINTENANCE section); reset the control and restart after correcting the problem; contact an Onan Dealer or Distributor for service if none of the above
Output voltage too high or low
Fix: Refer to Flow Chart C for the troubleshooting procedures
No fuel at injection nozzle but fuel to injection pump
Cause: Fuel solenoid may be defective
Fix: Listen for a click in injection pump when start switch is placed in the run position; if no click is heard and there is power to solenoid with the start switch in the run position, replace the fuel solenoid
No AC output voltage at rated engine RPM
Cause: Control panel field breaker CB3 not ON; field breaker open; residual voltage across TB2-2 and H1 less than 5 to 10 VAC; exciter field voltage across TB1-5 & 6 less than 5 VDC; defective diodes or SCR's on bridge assembly CR21; faulty exciter field wiring harness; open fuses F2 and F3 on VR21 regulator PC board; faulty exciter field winding; faulty reactor L21 or transformer T21; faulty voltage regulator assembly
Fix: Push to reset breaker; replace defective field breaker; flash exciter field per TEST [D]; disconnect stator leads 7 (4) and 8 (1) from TB2-2 and H1 and recheck residual voltage; check reactor L21 and transformer T21 per TESTS [B] and [E]; check diodes and SCR's on bridge assembly CR21 per TEST [C]; check exciter field wiring harness per TEST [M]; check fuses F2 and F3 for continuity on VR21 regulator PC board; check exciter field winding per TEST [H] and replace if bad; test voltage regulator assembly per procedure (S) and replace the regulator PC board per procedure (F) if defective
No AC output voltage at rated engine r/min
Fix: Refer to Flow Chart A for troubleshooting procedures

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan L634D.

Maintenance schedule

Item	Spec	Part #
Air filter	Guide, Valve Intake	110-3496	Amazon eBay
Fuel filter	Filter, Fuel	149-1754	Amazon eBay $54.34
Oil filter	Filter, Oil	122-0550	Amazon eBay $21.84 NAPA $18.20

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
Coolant Level	Check	50 hr
Crankcase Oil and Filter	Change	200 hr		First service — Perform after first 50 hours on new sets
Fan Belt	Check	50 hr
Generator Set	Inspect	50 hr		With engine running, visually/audibly check exhaust for leaks
Oil Level	Check	50 hr
Valve Lash Clearance	Check	400 hr		First service — Perform after first 50 hours on new sets; refer to L-Series Engine Service Manual
Air Cleaner	Check	100 hr		Perform more often under extremely dusty/dirty conditions
Exhaust Condensate Trap	Drain	100 hr
Fuel Level	Check	100 hr
Battery Condition	Check	200 hr
Electrolyte Level	Check	200 hr
Generator Assembly	Clean	200 hr
Air Cleaner Element	Change	400 hr
Crankcase Breather Cap (DL6TB)	Clean	400 hr
Fuel Filter	Change	400 hr	12 mo	Whichever comes first
Generator Bearing	Inspect	500 hr		Replace every five years

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	Trailer brake actuator stroke length	1	inch (25 mm)	maximum before brake shoe readjustment
Gap	Float switch test feeler gauge	0.125	inch (3 mm)	between float and C-clip stop
Gap	Magnetic pickup adjustment	1/2 turn out from tooth	turn	after contact with flywheel tooth
Gap	Overspeed switch air gap	0.005	inch (0.13 mm)	minimum
Gap	Overspeed switch air gap	not less than 0.005	inch (0.13 mm)
Gap	Overspeed switch magnetic air gap	0.005	inch (0.13 mm)	must not be less than
Gap	Overspeed switch magnetic air gap	0.005 inch (0.13 mm) minimum	inch
Other	Battery electrolyte specific gravity	1.260	specific gravity	fully charged battery at 80F (27C)
Other	Battery electrolyte specific gravity	about 1.260	specific gravity	fully charged at 80°F (27°C)
Other	Battery electrolyte specific gravity (fully charged)	about 1.260	specific gravity	at 80 deg F (27 deg C)
Other	Brake shoe adjustment	10	clicks	back off from point wheel cannot be turned by hand
Other	Control breaker rating	7	amperes
Other	Control heater element power	75	watts at 120 VAC
Other	Field breaker rating	5	amperes
Other	Low Oil Pressure Delay before shutdown/pre-alarm	7.5 to 12.5	seconds	after Start-Disconnect Relay energized
Other	Low oil pressure delay circuit	7.5 to 12.5	seconds	after start-disconnect relay energized
Other	Maximum allowable exhaust back pressure	41	inches (1041 mm) H2O
Other	Oil pressure gauge range	0 to 100 psi (0 to 700 kPa)	psi
Other	Overcranking timer cranking limit	45 to 75	seconds
Other	Overcranking timer limit	45 to 75	seconds
Other	Remote breaker rating	7	amperes
Other	Switching regulator (standard setting) nominal switching frequency	approximately 125	Hz
Other	Water temperature gauge range	100 to 250F (40 to 121C)	F
Pressure	Air cleaner cleaning air pressure	35	psi (241 kPa)
Pressure	Air cleaner rinse water pressure maximum	40	psi (276 kPa)
Pressure	Low oil pressure shutdown	14	psi	below; 97 kPa equivalent; 10 s delay after starter disconnect
Pressure	Low oil pressure shutdown	below 14	psi (97 kPa)	fault time delayed about 10 seconds following starter disconnect and inhibited during cranking
Pressure	Low oil pressure shutdown (LO OIL PRES)	14	psi (97 kPa)
Pressure	Low oil pressure switch closes	14	psi (97 kPa)
Pressure	Low oil pressure switch closes	14 psi (97 kPa)	psi
Pressure	Oil pressure gauge normal range	30 to 55	psi (207 to 380 kPa)	operating temperature
Pressure	Oil pressure gauge range	0 to 100	psi (0 to 700 kPa)
Pressure	Pre-low oil pressure alarm	20	psi (138 kPa) or less
Pressure	Pre-low oil pressure switch closes	20	psi (138 kPa)
Pressure	Pre-low oil pressure switch closes	20 psi (138 kPa)	psi
Pressure	Pre-low oil pressure warning	20	psi (138 kPa)
Resistance	Actuator coil resistance	1 ±10%	ohm	at 77°F (25°C); leads disconnected
Resistance	Commutating reactor L21 coils 1-2	0.031 to 0.37	ohms	at 77 deg F (25 deg C)
Resistance	Commutating reactor L21 coils 3-4	0.037 to 0.46	ohms	at 77 deg F (25 deg C)
Resistance	Commutating reactor L21/L22 coil 1-2 resistance	.031 to 0.37	ohms	at 77F (25C)
Resistance	Commutating reactor L21/L22 coil 3-4 resistance	0.037 to 0.46	ohms	at 77F (25C)
Resistance	Commutating reactor coil to frame	infinity	ohms
Resistance	Control heater element resistance	192	ohms	dissipates 75 watts at 120 VAC
Resistance	Exciter rotor leads T1-T2, T2-T3, T1-T3 resistance	0.6 to 0.7	ohms	at 68F (20C)
Resistance	Exciter rotor winding between lead pairs T1-T2, T2-T3, T1-T3	0.6 to 0.7	ohms	at 68 deg F (20 deg C)
Resistance	Exciter rotor winding resistance	0.54	ohms	at 77°F (25°C), ±10%
Resistance	Exciter rotor winding resistance	0.54 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter rotor winding resistance	0.645	ohms	at 77°F (25°C), ±10%
Resistance	Exciter rotor winding resistance	0.645 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator / rotor / generator winding insulation to ground	1 megohm (1,000,000 ohms) or greater	ohms	minimum
Resistance	Exciter stator field leads F1-F2 resistance	13.05 to 15.95	ohms	at 77F (25C)
Resistance	Exciter stator insulation resistance to lamination	100,000	ohms	minimum; 500 VDC or more
Resistance	Exciter stator winding between F1+ and F2-	13.05 to 15.95	ohms	at 77 deg F (25 deg C)
Resistance	Exciter stator winding resistance	12.4 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance	14.5 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, 4A2.3/6A3.4/6AT3.4	14.5	ohms	at 77°F (25°C), ±10%
Resistance	Exciter stator winding resistance, DGAB/DGAC/DGAD/DGAE	12.4	ohms	at 77°F (25°C), ±10%
Resistance	Exciter stator winding resistance, DL4	20.0	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, DL6	25.0	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, DL6T	40.0	ohms	at 77°F (25°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	Notes
Coolant	Ethylene glycol anti-freeze (permanent type) with rust/corrosion inhibitor, no stop-leak additive		Use at least 50/50 mixture of anti-freeze and clean, soft water
Engine oil	15W-40, 30W, 20, 20W-20, 10W (API CD/SF, CD/SE, or MIL-L-2104C); synthetic 5W-20 or 5W-30 (MIL-L-46167, MIL-L-2104C, MIL-L-46152B)	API CD/SF, CD/SE, MIL-L-2104C	Mineral base 5W-20/5W-30 not recommended under any conditions; select grade for lowest expected temperature
Fuel	ASTM 2-D (No. 2 Diesel) or ASTM 1-D (No. 1 Diesel), Cetane 45 minimum	ASTM 2-D / ASTM 1-D	Use No. 1 diesel below 0C (32F) and during long light-load periods; cloud point at least 10 degrees below lowest expected fuel temperature
Grease	MolyKote grease or equivalent		Apply thin film to mating surfaces of end bearing and end bell bearing hole
Grease	Molykote grease or equivalent		Apply a thin film to the mating surfaces of the end bearing and the end bell bearing hole.
Other	Approved water for battery electrolyte		Add approved water to keep battery electrolyte at proper level.
Other	DOT 3		Trailer brake system; reservoir should be at least half full
Other	DOT-3 heavy duty hydraulic fluid		Trailer brake system bleeding
Other	distilled water		Battery electrolyte; add distilled water to maintain proper level.

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
FAULT 1	Fault 1	Red lamp for customer-installed auxiliary equipment fault switch; part of timed factory-set 10-second shutdown circuit.	Shutdown
FAULT 2	Fault 2	Red lamp for customer-installed auxiliary equipment fault switch; part of factory-set non-timed delayed shutdown circuit.	Shutdown
HI ENG TEMP	High Engine Temperature	Engine overheated above 220F (104C) or low coolant	Shutdown	Check coolant level, airflow, fan belt
LO ENG TEMP	Low Engine Temperature	Engine block temperature below 70F (21C)	Info	Wait for block temperature to rise
LO FUEL	Low fuel	Yellow lamp indicates fuel supply is marginally low.	Warning	Replenish fuel supply.
LO OIL PRES	Low Oil Pressure	Oil pressure dropped to 14 psi (97 kPa)	Shutdown	Check oil level, reset control
LOW ENG TEMP	Low engine temperature	Yellow lamp indicates engine temperature is marginally low for starting; indicates inoperative coolant heater on gensets with option.	Warning	Check coolant heater.
LOW OIL PRES	Low oil pressure shutdown	Red lamp indicates engine shutdown because of critically low oil pressure.	Shutdown	Check oil level and LOP switch; inspect engine.
OVERCRANK	Overcrank	Engine failed to start after 45-75 seconds cranking	Shutdown	Check fuel system
OVERSPEED	Overspeed	Engine exceeded normal operating speed	Shutdown	Contact Onan Dealer or Distributor
PRE HI ENG TEMP	Pre-High Engine Temperature	Engine temperature approximately 215F (102C)	Warning	Check ventilation, reduce load
PRE HIGH ENG TEMP	Pre-high engine temperature	Yellow lamp indicates engine temperature is marginally high.	Warning	Find and correct cause.
PRE LO OIL PRES	Pre-Low Oil Pressure	Oil pressure dropped to 20 psi (138 kPa)	Warning	Check oil level
RUN	RUN	Green lamp comes on when both starter-disconnect circuits are opened after genset start.	Info
SWITCH OFF	Switch Off	Start/Stop/Remote switch in Stop position	Info	Move switch to Remote for automatic starting

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 magnetic pickup adjustment

Tools: Compressed air, Jam nut wrench

Rotate engine so ring gear tooth is centered in MPU hole.
Clean mounting hole with compressed air.
Turn MPU in until it contacts flywheel tooth directly below.
Turn out 1/2 turn and lock with jam nut.
Be sure pickup does not rotate when tightening jam nut.

Adjust voltage adjust potentiometer R21 adjustment

⚠ Contact with high voltage can cause severe personal injury or death.

Tools: Insulated screwdriver

Loosen locking nut of R21 and adjust to mid-range.
Start genset and bring temperature to normal.
With no load, turn Phase Selector to read output voltage and current.
Adjust R32 for approximate desired voltage.
Fine-adjust with R21 and tighten locking nut without changing setting.

Adjust voltage regulator adjustment

⚠ Use insulating mat or dry wood platform when control doors are open.

Tools: Insulated screwdriver, Accurate voltmeter

Open control panel doors and set S1, S2, and S3 per table.
Connect accurate voltmeter to TB1-2 and TB1-3 if no AC meter.
Start genset and bring temperature to normal.
Turn R32 to set no-load voltage.
Stop genset and close control panel doors.

Calibrate electronic governor adjustment

⚠ Keep hands and fingers clear while performing tests on operating equipment.

Tools: Tachometer or frequency meter

Check actuator linkage does not bind through full travel.
Attach tachometer or frequency meter.
Set GAIN adjustment to second mark from zero.
Disconnect governor rod from throttle lever.
Start genset and adjust right stop to 72 Hz for 60 Hz gensets.
Adjust left stop to take up slack and tighten locknut.
Stop, attach governor rod, start, and adjust SPEED to 60 or 50 Hz.
Connect load and adjust GAIN clockwise until stable.

Changing Sensitivity Reference adjustment

⚠ Do not mark on printed circuit boards with a pencil; graphite lines are conductive.

Tools: soldering iron

Unsolder W1 on VR21 at hole F for frequency sensitive.
Resolder W1 to hole S for semi-frequency sensitive.
Resolder W1 to hole N for non-frequency sensitive.

Electronic governor adjustment/calibration adjustment

⚠ Contact with rotating machinery can cause severe personal injury or death.

Tools: Tachometer or frequency meter, Screwdriver

Check actuator linkage does not bind through full travel; ensure terminals 7 and 8 are jumpered.
Attach tachometer to engine or frequency meter to generator if control panel lacks one.
Set Controller GAIN adjustment to second mark from zero.
Disconnect governor rod from throttle lever.
Place Run/Stop/Remote switch in Run position to start genset.
Adjust right stop screw on mechanical governor to obtain 72 Hz (2160 r/min) for 60 Hz gensets or 62 Hz (1860 r/min) for 50 Hz gensets.
Adjust left stop screw to just take up slack, then tighten locknut without binding shaft.
Stop genset, attach governor rod to throttle lever, start, and adjust Controller SPEED screw for 60 Hz or 50 Hz.
Connect full rated load; if genset cannot manage load, shorten governor rod one-half turn and repeat; tighten locknuts.
Connect 1/4 rated load; turn GAIN screw clockwise until actuator hunts, then back off until stable.
Stop genset, wait 30 seconds for turbo coast down if equipped, restart, and check for speed overshoot.
Restart genset and check frequency and stability under various loads.
Stop genset and remove tachometer or frequency meter if attached.

Fan Belt Adjustment adjustment

Tools: belt adjustment tool

Loosen alternator bolt through elongated slot in mounting bracket
Slide alternator until fan belt tension of 60 lbs (267 N) is obtained
Tighten alternator mounting bolt to lock in place
Check tension and repeat if necessary

Governor Control Adjustment adjustment

⚠ Hold the throttle linkage so that the set will not overspeed.

Tools: frequency meter

Place Start/Stop/Remote switch in STOP.
Attach frequency meter to generator output leads if none on panel.
Locate governor control in control box.
Adjust GAIN potentiometer fully counterclockwise.
Hold throttle linkage to prevent overspeed; start the set.
Adjust SPEED potentiometer to correct frequency (50 or 60 hertz).
Adjust GAIN clockwise until governor hunts, then counterclockwise until stable.
Test by tapping actuator lever; set should return to speed without hunting.
Stop and restart set to verify it does not overspeed.

Magnetic Pickup Sensor Adjustment adjustment

Place Start/Stop/Remote switch in the STOP position.
Loosen stop-nut on the magnetic sensor on the flywheel housing.
Turn sensor IN until it just contacts flywheel ring gear.
Back sensor OUT 1/2 turn and tighten stop-nut.

Reconnection (Test Q) adjustment

Refer to the generator reconnection possibilities when changing voltage.
Reconnect lead W12 (inside control box) to the proper H terminal (H2, H3, H4, H5, or H6) depending on voltage selected.
Change jumper W12 from TB2-2 to the proper TB2 terminal.

Voltage Adjustment (Standard Regulator) adjustment

Center the panel mounted voltage adjustment knob with pointer vertical.
Start the set and allow it to stabilize at correct frequency and speed.
Turn R18 counterclockwise to decrease voltage or clockwise to increase.
Set voltage with no load connected (e.g., 246 volts for 120/240).
Turn R26 counterclockwise until unstable, then clockwise until voltage stabilizes.

Voltage Adjustment (Test P) adjustment

Tools: voltmeter

Center the panel-mounted voltage adjustment knob vertically.
Start the set and allow it to stabilize at the correct frequency and speed.
Standard regulator: turn R18 counterclockwise to decrease voltage, clockwise to increase; set no-load voltage (e.g. 246 volts for 120/240 connection).
Standard regulator: turn R26 counterclockwise until voltage hunts, then clockwise until stable.
Switching regulator: turn R36 counterclockwise to increase voltage, clockwise to decrease; set no-load voltage.
Switching regulator: turn R5 counterclockwise until voltage hunts, then clockwise until stable.

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
		Connect loose wire W12 from TB2-2 to TB2 (H terminal)	H2, H3, H4, H5 or H6 depending on voltage selected	W12 reconnection lead inside control box; must be reconnected to proper H terminal when reconnecting for a different voltage
		X1 (red) to VR21-9, X2 (red) to VR21-10	X1, X2	Reference transformer T21 secondary connections
110/190	3			Figure 26 generator voltage connections
110/220	1	Connect lead W12 to H6 (per Figure 26 reconnection table)		50 Hz. Figure 26 generator voltage connections. OCR partially garbled.
115/200	3			Figure 26 generator voltage connections
115/230	1	Connect lead W12 to H6 (per Figure 26 reconnection table)		50 Hz. Figure 26 generator voltage connections. OCR partially garbled.
120/208	3			Figure 26 generator voltage connections
120/240	1	Connect lead W12 to H5 (per Figure 26 reconnection table)		60 Hz. Figure 26 generator voltage connections. OCR partially garbled.
120/240	1	Reconnectible generator (code 15/515)	W12 (TB2) to H3/H4/H5/H6 on voltage reference transformer	12-lead generator reconnection
127/220	3			Figure 26 generator voltage connections
130/400	3			Figure 26 generator voltage connections
139/240	3			Figure 26 generator voltage connections
208 VAC		Switch S1 position 1	stator T7 and T8	Transformer TX1 primary H1-H3
220/380	3			Figure 26 generator voltage connections
220/380	3	Non-reconnectible (code 7)	H3
240 VAC		Switch S1 positions 2 and 3	stator T7 and T8	Transformer TX1 primary H3-H5
240/416	3			Figure 26 generator voltage connections
254/440	3			Figure 26 generator voltage connections
277/480	3			Figure 26 generator voltage connections
347/600	3	Non-reconnectible (code 9X)	H5
Various		Reconnect lead W12 (inside control box) from TB2-2 to the proper H terminal (H2, H3, H4, H5, or H6) depending on voltage selected	W12, H2, H3, H4, H5, H6	Figure 25. Single phase generators use leads 1 and 4 (lead 2 not used); three phase generators use leads 4, 7, 8, 9 and 10 for control input and metering.

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 L634D?

The Cummins/Onan L634D engine has an oil capacity of 8.5 liters.

Which generators use the Cummins/Onan L634D engine?

The Cummins/Onan L634D powers 1 generator set(s), including Cummins/Onan DL6.

What is a common problem with the Cummins/Onan L634D engine?

A commonly reported issue on generators using the Cummins/Onan L634D is: Engine does not crank. Cause: Battery dead; start solenoid K1 does not energize; less than 7 volts DC between K1 terminal S and ground; less than 7 volts DC between B1 starter solenoid terminal and ground; K1 fault relay not energized; faulty battery cables or connections; faulty B1 starter solenoid or motor; faulty K1 start solenoid, K2 on/off relay, K3 and K11 start-disconnect relays, S10 switch, or connections. Fix: Check battery per Checkout [A] and recharge or replace; check alternator operation per Checkout [C]; check K1 start solenoid, K2 on/off relay, K3 and K11 start-disconnect relays, S10 switch, and all connections per Checkouts D, E, and G; check wiring and connections between K1 terminal I and the solenoid terminal B1; check for possible fault conditions and, if ok, check K1 fault relay per Checkout E; check battery cables for clean and tight connections per Checkout [B]; check B1 starter solenoid and motor and repair or replace if bad; jumper battery cable B+ connection to B1 starter solenoid terminal and check whether engine cranks.