Home›Engines›Cummins/Onan N52M

Cummins/Onan N52M Engine

The Cummins/Onan N52M is a 0.98 L 2-cylinder air-cooled engine rated at 3000 rpm, producing up to 14.5 kW. It powers generator sets from Cummins/Onan, including the N52.

Also known as: Onan N52M

0.976 L

Displacement

Cylinders

3000 rpm

Rated speed

14 kW

Gross power

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

Engine specifications

Displacement	0.976 L
Cylinders	2
Aspiration	Air-cooled
Rated speed	3000 rpm
Gross power	14 kW

Generator sets powered by this engine

Cummins/Onan N52

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

Service intervals

Item	Action	Hours	Months	Notes
Oil Level	Check	25 hr		First service — during break-in, every 5 operating hours
Exhaust system	Inspect	8 hr		Maintenance schedules recommend inspection every eight hours by owner/operator for RV generator set exhaust systems.
Crankcase Oil	Change	25 hr		N52M service interval (footnote 1)
Engine Generally	Inspect	25 hr
Governor Linkage	Clean	50 hr
Spark arrester/muffler, screen type	Clean	50 hr		Remove and scrape clean or replace screen; may be blown clean with compressed air. Every 50 operating hours.
Spark arrester/muffler, spin-out type	Clean	50 hr		Remove pipe plug in bottom of muffler and run set for 5 minutes; replace plug. Every 50 hours of set operation.
Spark arresters	Clean	50 hr		Spark arresters should be cleaned every 50 to 100 hours; routine cleaning during servicing is good safety practice.
Spark plugs	Replace	100 hr		Annually or every 75 hours, whichever occurs first, for B43M/B48M/BF/BG/N52M engines.
Breaker Points	Check	100 hr
Air Cleaner Element	Replace	200 hr
Cooling Fins	Clean	200 hr
Fuel System	Clean	200 hr
Stainless steel spark arrester screen	Replace	500 hr		For units using specially designed stainless steel screens.
Flexible fuel lines	Replace		60 mo	Replace every five years as a precautionary measure; check at each service.

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 Bearing	0.0015-0.003	in	min-max
Clearance	Camshaft End Play	0.003	in	max
Clearance	Connecting Rod End Play	0.002-0.016	in	min-max
Clearance	Crankshaft End Play	0.005-0.009	in	min-max
Clearance	Crankshaft Main Bearing	0.0025-0.0038	in	min-max
Clearance	Crankshaft Main Bearing Journal - Standard Size	1.9992-2.0000	in	standard size
Clearance	Crankshaft Rod Bearing Journal - Standard Size	1.6252-1.6260	in	standard size
Clearance	Cylinder Bore - Standard Size	3.5625-3.5635	in	standard size
Clearance	Front gear cover oil seal installation depth	1-1/32	in	rear spring side of casing from gear cover mounting face
Clearance	Fuel injection pump installation dimension	3.260	in	new camshaft; instead of 3.254
Clearance	Oil Pump Gear Back Lash	0.002-0.005	in	min-max
Clearance	Oil pump gear backlash	0.005	in
Clearance	Piston Pin in Rod	0.0001-0.0005	in	min-max
Clearance	Piston Ring Gap in Cylinder	0.010-0.020	in	min-max
Clearance	Piston to Cylinder Clearance, Light Weight (No Strut)	0.0065-0.0095	in	min-max
Clearance	Piston to Cylinder Clearance, Strut Type	0.0015-0.0035	in	measured below oil-control ring 90° from pin
Clearance	Rod Bearing to Rod Journal Clearance	0.0005-0.0023	in	min-max
Clearance	Starter gear lash	.020 - .010	in	pinion/ring gear engagement
Clearance	Timing Gear Back Lash	0.002-0.003	in	min-max
Clearance	Valve Seat Interference Width	1/32-3/64	in	min-max
Clearance	Valve Stem in Guide - Exhaust	0.0025-0.004	in	min-max
Clearance	Valve Stem in Guide - Intake	0.001-0.0025	in	min-max
Gap	Breaker Point Gap (NHA, NHB, NHC, NHAV, NHBV, NHCV)	0.016	in
Gap	Breaker Point Gap - N52M	0.020	in
Gap	Point gap	0.016	in	equals 20 degrees BTC ignition timing and spark advance
Gap	Spark Plug Gap (Gas)	0.018	in
Gap	Spark Plug Gap (Gasoline)	0.025	in
Gap	Spark Plug Gap (N52M all fuel)	0.030	in
Gap	Spark plug gap	.035	in	increased from .025 (0.64 mm) for light-load smoothness
Other	Carburetor main jet adjustment	1-1/2 to 1-3/4	turns open	NHC-MS normal adjustment
Other	Ignition Timing Battery (NH)	22	°BTC
Other	Ignition Timing Battery (NHA, NHB, NHC)	20	°BTC
Other	Ignition Timing Battery N52M	25	°BTC
Other	Ignition Timing Magneto (NH) - Running	22	°BTC	running
Other	Ignition timing with spark advance	24	degrees BTC	after initial timing change to 5 degrees BTC
Other	Initial ignition timing	5	degrees BTC	CCKB-MS/2861J and CCKB-MS/2900J magneto ignition with electric start
Other	Injection timing advance	2	crank degrees	4-cylinder J Series diesel; advance from 19 to 21 degrees BTC PC
Other	Piston Pin in Piston	Thumb Push Fit
Other	Rotor diameter	4.420	in	acceptable; replace rotors measuring 4.415 in or less
Other	Valve Face Angle	44	°
Other	Valve Seat Angle	45	°
Pressure	Low oil pressure while cranking	8-10	lbs	2.7 AJ RV with LOPKO
Pressure	Normal oil pressure at operating temperature	20	PSI	2.7 AJ RV
Resistance	Unijunction transistor B1-B2	5000	Ohms	361-0004; Simpson 260 on R x 10,000 scale
Resistance	Unijunction transistor E-B2	7000	Ohms	361-0004; Simpson 260 on R x 10,000 scale
Speed	Full-load engine speed	1770	RPM	59 Hz or 110 volts
Speed	Idle stop speed	1500	RPM	50 Hz or 100 volts
Speed	No-load engine speed	1860	RPM	62 Hz or 130 volts
Torque	Bearing plate adapter fasteners	25-27	Lbf-ft	same as rear bearing plate
Torque	Breaker box socket head screws	5-7	ft. lbs.	after timing is set
Torque	Connecting Rod Bolt - Forged Aluminum	14-16	ft.lb.
Torque	Connecting Rod Bolt - Nodular Iron	27-29	ft.lb.
Torque	Cylinder Head Bolt (Standard)	17-19	ft.lb.
Torque	Cylinder Head Bolt W/Compression Washer	13-15	ft.lb.
Torque	Cylinder head nut	13-15	ft. lbs.	N52M-GA019.9 with two compression washers on upper 6 bolts; torque in three 5 ft. lb. steps
Torque	Cylinder head nut with compression washers	15	foot pounds	when 851-0025 spring washers are used; standard is 18 foot pounds
Torque	Delivery valve cap nut	55-60	ft lbs	PSU injection pump
Torque	Delivery valve holder	70-75	ft. lbs.	PSU injection pump
Torque	Exhaust Manifold (NHA, NHB, NHC)	10-12	ft.lb.
Torque	Exhaust manifold mounting hardware	14-17	foot lbs.

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 base anti-freeze mixed with water		Do NOT use straight 100% ethylene glycol. Normal mixture approximately 50% anti-freeze and 50% water; ratio varies with ambient temperature.
Engine oil	API SE or SE/CC	API	Use low ash content oils .03-.85 percent by weight with natural gas or propane fueled engines. See SAE viscosity grades chart.
Fuel	ASTM 2-D or 1-D diesel fuel	Cetane number 45	Use Number 1-D diesel fuel when ambient temperatures are below 32 F (0 C) or during long periods of light load/cyclic operation.
Fuel	Unleaded or regular grade gasoline		Use regular gasoline for first 25 hours to allow rings to seat; then use unleaded. Do not use highly leaded premium fuels.

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 anti-dieseling solenoid adjustment

With set stopped, turn lever counterclockwise; set screw so plates are closed but not binding.
Check lever has approximately 30 degrees travel counterclockwise from vertical.
Start set; lever should rotate approximately 60 degrees clockwise from stopped position.
Check solenoid plunger is fully seated.
If not, adjust distance between plunger and lever arm; repeat steps.

Carburetor Adjustments adjustment

⚠ Forcing needle against seat will damage it.

Tools: Carburetor adjusting wrench 420-0294 or 420-0169

Allow engine to reach normal operating temperature before adjustments.
Idle Jet Adjustment: With no load, move speed control to SLOW. Turn idle jet needle out until engine loses speed, then in until runs smooth.
Throttle Stop Adjustment: Adjust screw so throttle maintains 1/32 inch from manifold.
Main Jet Adjustment: Apply full load. Grasp governor mechanism to minimum speed. Release and observe acceleration. If uneven, turn main adjustment out 1/4 turn. Do not open needle more than 1/2 turn b

Carburetor adjustment for 6.5 NH RV adjustment

Turn idle mixture screw out 3/4 to 1 turn from seated.
Turn main mixture screw 1-1/2 to 1-3/4 turns out from seated.
Start set; adjust governor spring for 1860 RPM no load (62 Hz or 130 volts).
Hold governor arm so throttle lever rests on stop; adjust idle stop screw to 1500 RPM (50 Hz or 100 volts); release.
Adjust idle mixture screw to highest RPM or voltage; readjust governor spring to 1860 RPM no load.
Apply full load; adjust main mixture screw to highest RPM or voltage; readjust governor spring to 1770 RPM full load.
Remove and add load several times to check hunting; readjust governor spring if required.

Check Valve Clearance adjustment

Tools: Feeler gauge, Valve tappet adjusting wrench 420-0139

Set valve clearance to .003" on intake and .012" on exhaust.
Place one cylinder on compression stroke and adjust those valves.
Turn crankshaft one full turn placing other cylinder on compression and adjust its valves.

Float Level Adjustments adjustment

Measure float setting at bowl flange.
For downdraft carburetors, dimension should be 1/4 inch.
For LUA carburetors, measure float setting as indicated.

Governor Adjustments adjustment

Tools: Tachometer

Make governor adjustments concurrent with carburetor adjustments.
Linkage Adjustment: Adjust length so with engine stopped and tension on governor spring, stop on carburetor throttle lever is 1/32 inch from carburetor stop boss.
Speed Adjustment: Check speed with tachometer. Turn speed adjusting nut IN to increase speed or OUT to decrease.
Sensitivity Adjustment: Move spring toward governor shaft to increase sensitivity; toward linkage end to decrease.
Low Speed Stop Adjustment: Set screw for approximately 50 to 100 rpm above throttle stop screw setting. Preferred speed is 1000 rpm.

Set Point Gap adjustment

Tools: Feeler gauge

Rotate engine crankshaft clockwise until maximum breaker point gap is obtained.
Turn cam screw until proper point gap is measured with a feeler gauge.
Wipe gauge before measuring to remove oil or foreign material.

Check symmetrical firing of rectifier bridge 305-0524 diagnostic

Tools: Simpson 260 meter, diode 357-0014 or 357-0004

Run unit at no load. Use Simpson 260 on 2.5 VDC positive scale.
Connect positive meter lead to plus terminal on 305-0524 module.
Connect negative lead to anode of diode 357-0014 or 357-0004; connect cathode to AC1 and record reading.
Move cathode to AC2 and record reading. Stop engine.
Reverse secondary leads X1 and X2 of transformer T21 at positions 9 and 10 on regulator board.
Start engine and repeat readings.
Connect T21 secondary leads to positions giving least voltage difference.

Field flashing to restore AC output diagnostic

Tools: field flashing tool

Flash the field.
Check capacitor C1; replace if suspected defective.
Check diodes CR1 and CR2; replace if defective.
If still no output, refer to Generator and Controls Master Service Manual section 6.

Apply RTV sealant to cylinder head gasket 110-1852 maintenance

Tools: White RTV sealant

Apply White RTV sealant bead .03-.06 thick on both sides of head gasket.
Alternatively apply RTV to finished block surface and one side of gasket.
Install gasket before RTV hardens.
Allow minimum cure time one hour before operating engine.
Water or water vapor accelerates curing.

Break-In Procedure maintenance

⚠ Using wrong grade and weight of oil can cause high engine operating temperatures during break-in causing engine damage.

Run engine at half load for first three hours with intermittent periods of full load.
Check oil level at least every five operating hours.
Add oil to keep at proper level; never overfill as overfilling may cause oil to foam and enter breather system.

Clean external oil lines and restricted fittings maintenance

⚠ Do NOT enlarge orifice or substitute fittings.

Tools: #70 drill (.028), #56 drill (.046), low pressure compressed air

Remove and clean oil lines and passages with low pressure compressed air during major service.
Single cylinder: clean restricted fitting at cylinder head oil line with #70 drill (.028).
Clean low oil pressure switch tee with #70 drill (.028).
Two cylinder: clean cylinder head fitting with #70 drill; clean tee between oil filter adapter and injection pump pad with #56 drill (.046).
Four cylinder: clean each cylinder head fitting with #70 drill; clean connector coupling with #56 drill (.046).
Blow all lines and fittings clean before installation.

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 displacement of the Cummins/Onan N52M?

The Cummins/Onan N52M has a displacement of 0.976 liters with 2 cylinders.

Which generators use the Cummins/Onan N52M engine?

The Cummins/Onan N52M powers 1 generator set(s), including Cummins/Onan N52.