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Cummins/Onan E125V/E140V Engine

The Cummins/Onan E125V/E140V is a 1-cylinder engine rated at 3600 rpm. It powers generator sets from Cummins/Onan, including the E125 and E140. It holds 1.6 L (0.4 gal) of oil.

Also known as: Onan E125V/E140V

Part of the Cummins/Onan E125V engine family — 2 variants share parts & fitment.

Cylinders

3600 rpm

Rated speed

1.6 L

Oil capacity

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

Engine specifications

Oil capacity	1.6 L
Cylinders	1
Rated speed	3600 rpm

Generator sets powered by this engine

Cummins/Onan E125 Cummins/Onan E140

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

Common problems

Weakness and Sleepiness
Fix: Get out into fresh air immediately, shut down the unit and do not use it until it has been inspected.
Vomiting
Fix: Get out into fresh air immediately, shut down the unit and do not use it until it has been inspected.
The engine runs and then stops.
Fix: A. Check the fuel tank and fill if necessary. b. Check the engine oil level and add oil as necessary. Drain excess oil if the level is above the dipstick Full mark. c. Reconnect and reclamp the choke and throttle cables, if necessary. See Adjustments.
The engine fails to crank (electric start engines).
Fix: A. Release the clutch (if so equipped). b. Clean and tighten the positive (+) and negative (–) battery cable connections at the battery and the engine. c. Recharge the battery. Refer to the equipment or battery manufacturer’s recommendations.
The engine exhausts black smoke.
Fix: A. Service the air cleaner. b. Reconnect and reclamp the choke and throttle cables, if necessary. See Adjustments.
The engine cranks slowly (electric start), or the recoil starter is hard to pull.
Fix: A. Release the clutch (if so equipped). b. If electric start, clean and tighten the positive (+) and negative (–) battery cable connections at the battery and the engine. c. If electric start, recharge the battery. Refer to the equipment or battery manufacturer’s recommendations. d. Change engine oil to oil having the proper viscosity for the ambient temperature. See Table 1.
The engine cranks but fails to start.
Fix: A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Reconnect and reclamp the choke and throttle cables, if necessary. See Adjustments. e. Service the air cleaner. f. Replace the fuel filter(if provided). g. Inspect and clean or replace the spark plug and re-gap it.
Muscular Twitching
Fix: Get out into fresh air immediately, shut down the unit and do not use it until it has been inspected.
Inability to Think Coherently
Fix: IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the engine and do not operate it until it has been inspected and repaired.
Dizziness
Fix: Get out into fresh air immediately, shut down the unit and do not use it until it has been inspected.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan E125V/E140V.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Clean the air cleaner more often than normal as required. See Table 2.		—	200 hr
Fuel filter			—	400 hr
Oil filter			—	200 hr
Battery	Check the battery more frequently. See Periodic Maintenance and any instructions available from the equipment or battery manufacturer.		—	400 hr
Belt			—
Coolant			—
Oil	API classification, use Class SG or SH oil (also SG/CD, SG/CE, SH/CD or SH/CE)	1.6 l	—	24 hr
Spark plug			—	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	Months	Notes
Genset	Other	2 hr	1 mo	Exercise at least 2 hours each month at approximately 1/2 rated power; a single 2-hour period is better than several shorter ones
Engine	Inspect	8 hr		Daily or every 8 hours; check for oil, fuel and exhaust leaks, loose parts and unusual noises and vibrations
Engine oil level	Check	8 hr		Before first start of day and after every 8 hours
Exhaust System	Inspect	24 hr		Daily or every 8 hours
Fuel Lines	Inspect	8 hr		Daily or every 8 hours
General inspection	Inspect	8 hr		Before first start of day and after every 8 hours of operation (Table 4)
Oil Level	Check	8 hr		Keep between Full and Add marks on dipstick.
Air Cleaner Foam Wrapper	Clean	50 hr		Perform more often in dusty conditions.
Cylinder Cooling Fins	Clean	50 hr		Perform more often in dusty conditions.
Engine Oil	Change	100 hr		First service — Also after first 24 hours of operation as part of engine break-in; perform more often in dusty/hot conditions
Engine Oil and Oil Filter	Change	150 hr		First service — Perform more often in hot or dusty conditions.
Spark Plug	Inspect	100 hr		Inspect, clean and re-gap.
Spark arrestor	Clean	150 hr		Spark arrestor muffler cleanout; Table 4 column inferred
Air Cleaner Element	Replace	200 hr		Perform more often in dusty conditions.
Engine Oil Filter	Change	200 hr		First service — Also after first 24 hours of operation as part of engine break-in; perform more often in dusty/hot conditions
Engine Valve Clearance	Adjust	500 hr		First service — Must be performed by a qualified mechanic.
Fuel Filter	Replace	200 hr		If so equipped.
Carburetor and combustion chambers	Clean	300 hr		Clean with Onan "4C"; Table 4 column inferred
Engine air filter	Replace	300 hr		Footnotes 2,4 — more often in dusty conditions, at least once a year
Spark Plug	Replace	400 hr
Choke vacuum sustain valve	Replace	500 hr		Footnotes 5,6 — sooner if performance deteriorates; qualified mechanic
Cylinder heads and combustion chambers	Clean	500 hr		Remove cylinder heads and clean combustion chambers; footnote 6
Engine cooling fins	Clean	500 hr		Footnotes 2,6
Fuel filter(s) and fuel pump screen	Replace	500 hr		Footnotes 5,6 — replace filter(s) and clean fuel pump screen
Governor linkage	Inspect	500 hr		Inspect and clean; footnote 6
Spark plugs	Replace	500 hr		Footnote 4 — at least once a year; Table 4 column inferred
Cylinder Heads of Deposits	Clean	1000 hr		Clean more often when using leaded fuel or running continuously under light load; Onan 4C cleaner recommended every 200 hours
Starting Battery	Check		1 mo	See instructions for battery care provided by equipment or battery manufacturer
Starting battery	Clean		1 mo	Clean and check starting battery; footnote 3 — perform more often in hot weather

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	Connecting rod large bore clearance	0.015-0.050	mm	allowable limit 0.100
Clearance	Connecting rod side clearance on crankshaft	0.40-1.10	mm	allowable limit 1.50
Clearance	Cylinder bore I.D. standard	84.200-84.225	mm	factory specification; allowable limit 84.325
Clearance	Cylinder bore out-of-round allowable limit	0.05	mm	0.002 in
Clearance	Cylinder bore taper allowable limit	0.10	mm	0.004 in
Clearance	Tailpipe extension beyond perimeter of vehicle	at least 1 inch (25.4 mm)
Clearance	Valve stem to valve guide clearance (exhaust)	0.04-0.08	mm	allowable limit 0.10
Clearance	Valve stem to valve guide clearance (intake)	0.03-0.06	mm	allowable limit 0.10
Gap	Magneto coil to rotor magnet clearance (air gap)	0.25-0.40	mm	0.010-0.016 in
Gap	Spark Plug Gap	0.025	inches (0.64 mm)
Gap	Spark Plug Gap	0.035	inches
Gap	Spark Plug Gap	0.035 inches (0.89 mm)	inches (mm)
Gap	Spark Plug Gap	0.89	mm
Gap	Spark plug gap	0.025 inches (0.64 mm)
Gap	Spark plug gap	0.89-1.02	mm	0.035-0.040 in
Other	Battery electrolyte specific gravity — recharge below	1.215
Other	Battery electrolyte specific gravity — stop charging at	1.260		at approximately 80° F (27° C)
Other	Bore	84.2	mm
Other	Carburetor CO adjustment	5% to 6% CO at 3300 rpm	CO	no load; without meter set idle mixture screw 2 turns out
Other	Compression Ratio	7.0 : 1
Other	Compression Ratio	8.5	:1
Other	Cylinder bore	3.250 inches (83 mm)
Other	Cylinder bore	3.563 inches (90 mm)
Other	Displacement	48	inches3 (782 cc)
Other	Displacement	48 inches3 (782 cc)
Other	Displacement	60 inches3 (980 cc)
Other	Engine oil capacity (with filter)	3.5 quarts (3.3 l)
Other	Fuse F1 (control circuit)	5 amperes
Other	Fuse F2 (autochoke/fuel pump; fuel solenoid on LPG)	10 amperes mini-bayonet
Other	Genset power (BGE LPG, 50 Hz)	4800 watts; 120 volts; 40 amperes
Other	Genset power (BGE, 60 Hz)	4000 watts; 120 volts; 33.3 amperes
Other	Genset power (NHE, 50 Hz, 1-phase)	5000 watts; 110/220 or 120/240 volts; 45.5/22.7 or 41.7/20.8 amperes; 1500 RPM
Other	Genset power (NHE, 60 Hz, 1-phase)	6500 watts; 110/220 or 120/240 volts; 54.2 amperes; 1800 RPM
Other	Ignition Timing	20° BTDC		Non-adjustable electronic ignition
Other	Ignition Timing	23	° BTDC	non-adjustable, electronic magneto ignition
Other	Ignition Timing	23° BTDC	degrees BTDC	Non-adjustable, electronic, magneto ignition
Other	Ignition timing (electronic ignition)	12° BTDC, non-adjustable
Other	Ignition timing (not adjustable)	23	degrees BTDC	fixed by flywheel magnet to shaft keyway relationship
Other	Minimum battery cold cranking capacity above freezing	360 amperes		above freezing
Other	Minimum battery cold cranking capacity below freezing	450 amperes		below freezing
Other	Power decrease with altitude	approximately 3.5 percent of rated power each 1000 feet (305 m)
Other	Stroke	2.875 inches (73 mm)
Other	Stroke	3.000 inches (76 mm)
Other	Stroke	70.0	mm
Pressure	12 VDC system voltage regulator output	13.6-14.7	VDC	@ any speed within operating range
Pressure	LPG vapor supply pressure (vapor-withdrawal models only)	9 to 13 inch (229 to 330 mm) W.C. (water column)
Pressure	Minimum cylinder compression test pressure	483	kPa	warm engine at cranking speed (about 300 rpm); 70 psi
Resistance	Alternator stator resistance	5 amp system: 0.54 to 0.66; 20 amp system: 0.27 to 0.33	Ohms
Speed	High Idle Speed	3400	RPM	recommended
Speed	High-Idle Speed	3400	RPM	recommended in absence of equipment specifications
Speed	Low Idle Speed	1100	RPM	recommended
Speed	Low Idle Speed	1400	RPM	recommended if no equipment spec
Speed	Low-Idle Speed	1400	RPM	recommended in absence of equipment specifications
Speed	Rated speed	1800 RPM (60 Hz) / 1500 RPM (50 Hz)
Speed	Recommended high-idle engine speed	3400	RPM	when equipment manufacturer spec not available
Speed	Recommended low-idle engine speed	1400	RPM	when equipment manufacturer spec not available
Torque	Adapter Filter Head	47-54	N-m	3/4"-16 (35-40 lb-ft)
Torque	Air Cleaner Pan to Cylinder Block	11-16	N-m	M8 x 16 (8-12 lb-ft); tighten twice (1-2-1)
Torque	Alternator Stator Screws	10-15	N-m	M6 x 25 (7-11 lb-ft)
Torque	Blower Housing Bolts	7-11	N-m	M6 x 20 (5-8 lb-ft)

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
Engine oil	5W-30	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-28°C to 10°C	1.9 l
Engine oil	10W-30	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-18°C to 27°C	3.5	0° F to 80° F
Engine oil	10W-30 or 10W-40	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-18°C to 27°C	1.9 l
Engine oil	10W-40	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-18°C to 27°C	3.5	0° F to 80° F
Engine oil	15W-40	API SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-12°C to 38°C	1.6 l	OnaMax
Engine oil	15W-40 (OnaMax)	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	-12°C to 38°C	1.9 l
Engine oil	SAE 30	API Class SG or SH (also SG/CD, SG/CE, SH/CD or SH/CE)	above 0°C	1.9 l	Single-grade SAE 30 oil is preferable when temperatures are consistently above freezing.
Fuel	HD-5 grade liquified petroleum gas or equivalent, at least 90 percent propane				Commercial LPG may contain more than 2.5 percent butane, causing poor vaporization below 32° F (0° C)
Fuel	Unleaded gasoline	Minimum octane rating (Anti-Knock Index) of 87			Do not use gasoline or additives containing methanol. Leaded gasoline may be used but increases maintenance.
Fuel	Unleaded gasoline, minimum octane rating (Anti-Knock Index) 87				Do not use gasoline or additives containing methanol; leaded gasoline may be used but increases maintenance
Fuel	unleaded gasoline	minimum octane rating (Anti-Knock Index) of 87			Do not use gasoline or gasoline additives containing methanol. Leaded gasoline may be used but will result in extra maintenance.

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

Procedures

Adjusting Valve Lash adjustment

Tools: feeler gauge

Engine must be at room temperature.
Remove the valve rocker cover and spark plug.
Turn engine over until piston is at COMPRESSION TOP DEAD CENTER.
Check intake and exhaust valve lash with a feeler gauge.
Loosen locknut and turn lash adjusting screw until specified lash obtained.
Tighten locknut and recheck lash.

Choke Adjustment adjustment

Tools: 1/8 inch drill bit, wrench

Shut off engine, remove air cleaner outer cover and filter element.
Loosen choke rod swivel clamp screw.
Lock throttle control lever with pin (1/8 inch drill bit) so pin acts as stop for choke lever.
Push choke rod towards carburetor to fully open choke.
Rotate choke lever towards carburetor until it bears against pin stop, tighten swivel clamp screw.
Remove lock pin and check choke linkage operation. Replace damaged components.
Reassemble air cleaner.
Adjust throttle and choke control cables.

Control Cable Adjustments adjustment

Tools: 1/8 inch drill bit, wrench

For single-cable: shut off engine, loosen throttle cable clamp.
Lock throttle lever with pin (1/8 inch drill bit).
Push speed control lever to high speed position.
Hook cable wire into throttle lever, pull out slack, tighten clamp. Remove lock pin.
For two-cable: repeat steps 1-3, then push choke knob to full-open.
Hook choke cable wire into choke lever, push choke rod towards carburetor, pull out slack, tighten clamp.

Engine Speed Adjustment adjustment

⚠ Adjusting the engine speed to a value above that specified by the equipment manufacturer could cause the equipment to operate at speeds in violation of Federal and State Standards for Safety for the equipment.

⚠ Moving parts can cause severe personal injury or death. Take care when measuring engine speed with a tachometer and follow the meter instructions. You must be a qualified mechanic.

Tools: tachometer

Normally no need to adjust engine speed. Instructions are for equipment manufacturer. Attempt only by qualified mechanic using accurate tachometer.
Set low-idle and high-idle speeds to values specified in equipment Operator's Manual. If absent, adjust low-idle to 1,100 RPM and high-idle to 3,400 RPM.
Start engine, observing all equipment manufacturer's instructions and precautions.
If throttle cable already connected, loosen clamp at engine and back out low-idle speed stop screw so speed stop screw on carburetor touches its stop. Adjust engine speed to 1,000 RPM with carburetor
Turn low-idle speed stop screw to obtain specified low-idle speed.
Move engine throttle link up against its stop tang and hold it there while bending tang as necessary to obtain specified high-idle speed.
Hook engine throttle link with throttle cable, pull slack out of throttle cable and tighten clamp. Check for full, smooth movement of engine throttle link between its two stop positions when equipment

Engine Speed Adjustments adjustment

⚠ Adjusting engine speed above equipment manufacturer specification may violate Federal and State safety standards.

Tools: accurate tachometer

Start engine and move throttle lever to lowest speed position.
Adjust low-idle speed stop screw on carburetor to specified low-idle speed.
Move throttle lever to highest speed position.
Loosen high-idle stop plate clamping screw and rotate plate to specified speed; retighten.
For lever controlled engines adjust lever stop screw instead.
Check full smooth movement of throttle control arm between stop positions.

Governor Arm Adjustment adjustment

⚠ Disconnect spark plug and battery negative cable before adjusting the governor.

Loosely assemble governor arm to governor shaft and start the lock nut.
Re-attach link to governor arm and carburetor; replace worn clips.
Push top of governor arm toward carburetor until it stops and hold.
Check governor spring pulls carburetor throttle to wide open.
Tighten lock nut; ensure governor shaft rotates clockwise against internal parts.
Tighten to Section 3 torque specifications.

Reconnecting and Reclamping the Choke and Throttle Cables adjustment

⚠ Accidental starting can cause severe personal injury or death.

Stop engine and disconnect spark plug and battery negative cable.
Push choke knob to full open-choke; set throttle lever to lowest speed.
Loosen cable clamp at engine bracket if necessary.
Hook cable wires into hook holes in choke and throttle control arms.
Rotate control arms clockwise, hold against stops, pull out cable slack, tighten clamp.
Check smooth movement and full travel of choke knob and throttle lever.
Reassemble air cleaner and reconnect spark plug and battery.

12 VDC Output System Tests diagnostic

⚠ Reversed battery connections or operation without a battery will damage the voltage regulator and/or alternator stator.

Tools: multimeter (Simpson 270)

Check battery voltage with engine not running; charge if out of specification.
With engine running, check voltage regulator output at battery terminals.
Disconnect stator leads from regulator and test stator AC output.
Shut down engine and check resistance between each stator lead and ground.
Check stator resistance across stator leads with ohmmeter.
Replace stator if resistance out of specification.
Replace flywheel assembly if stator resistance is correct but output low.

Air Cleaner Element Replacement maintenance

Pull choke knob to full-choke position to close choke plate.
Remove outer cover; wipe away loose dust and debris.
Remove mounting nut, inner cover and air cleaner element.
Wipe dust and debris from the air cleaner base.
Install new paper element and secure with inner cover and mounting nut.
Tighten nut 1-1/2 turns after seating it on the cover.
Reinstall foam wrapper and outer cover.

Air Cleaner Maintenance maintenance

Refer to Table 2 for scheduled foam wrapper maintenance and air cleaner element replacement. See Figure 4.
For foam wrapper only: do not remove inner air cleaner cover. Remove and wash foam wrapper in water and detergent.
Squeeze foam wrapper dry like a sponge. Rinse with clean water and allow to dry.
Coat wrapper evenly with one tablespoon (14 grams) of SAE 30 engine oil. Knead oil into wrapper and wring out excess oil.
Install foam wrapper over paper air cleaner element by stretching it over inner cover. Completely cover all exposed paper pleats.
Replace foam wrapper when it becomes torn or stretched.
For element replacement: pull choke knob to full-choke position to close choke plate. Remove outer cover and wipe away loose dust and debris.
Remove inner air cleaner mounting nut and cover.
Remove air filter paper element and foam wrapper from engine. Wipe off dust and debris from air cleaner base.
Install new paper element and secure with inner cover and mounting nut. Reinstall foam wrapper and outer cover. Reconnect crankcase breather tube.

Air Filter Replacement maintenance

Remove the through-bolt and cover.
Reassemble with a new air filter element and wrapper.
Do not over-tighten the through bolt.

Battery Care maintenance

⚠ Batteries give off explosive gases; do not smoke or allow flames or sparks near batteries

⚠ Battery electrolyte can cause severe eye damage and skin burns

Tools: Terminal puller tool, Battery hydrometer, Goggles, Rubber gloves, Protective apron

Keep the battery case clean and dry.
Make certain battery cable connections are clean and tight.
Remove the negative (-) cable first and connect it last.
Remove corrosion with an ammonia or baking soda solution; flush with clean water.
Add distilled water to each cell to the split-level marker if not maintenance-free.
Check specific gravity of each cell with a hydrometer; charge if below 1.215.
Stop charging when specific gravity reaches 1.260 at approximately 80° F (27° C).

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

Parts cataloged across the Cummins/Onan E125V family

Part #	Description	Category
140-2331	Air Cleaner Element	Air filter
140-2335	Air Cleaner Element Wrapper (If Equipped)	Element wrapper
149-2206-01	Fuel Filter	Fuel filter
122-0737	Filter	Oil filter
965-0178	E125V/ E140V	Service part / kit
965-0179	E125H I E140H	Service part / kit
965-0180	P218V I P220V	Service part / kit
965-0183	P248V Floorcare	Service part / kit
C851D8	pin (1/8 inch drill bit)	Service part / kit
167-0765	Spark Plug	Spark plug

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Common questions

What is the oil capacity of the Cummins/Onan E125V/E140V?

The Cummins/Onan E125V/E140V engine has an oil capacity of 1.6 liters.

Which generators use the Cummins/Onan E125V/E140V engine?

The Cummins/Onan E125V/E140V powers 2 generator set(s), including Cummins/Onan E125, Cummins/Onan E140.

How often should you change the oil in the Cummins/Onan E125V/E140V?

The Cummins/Onan E125V/E140V oil change interval is every 24 hours.

What is a common problem with the Cummins/Onan E125V/E140V engine?

A commonly reported issue on generators using the Cummins/Onan E125V/E140V is: Weakness and Sleepiness. Fix: Get out into fresh air immediately, shut down the unit and do not use it until it has been inspected..