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GN550-DG-A3 Engine

The GN550-DG-A3 is an engine. It powers generator sets from Cummins/Onan, including the K400.

Also known as: GN550-DG-A3

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

Engine specifications

Generator sets powered by this engine

Cummins/Onan K400

Common problems

Only slight output voltage is delivered (3 ~ 6V)
Cause: Worn brush or faulty contact surface of slip ring
Fix: Clean brush contact and slip ring, or replace brush
Rated output voltage is not available
Cause: Abnormal load circuit, blown circuit breaker (S.T.D., voltage 10%)
Fix: Remove abnormality in load circuit and replace fuse
Pilot lamp does not light and output voltage is OV
Cause: Faulty contact of receptacles or disconnected wiring inside of control box
Fix: Repair or replace
Output voltage is not delivered
Cause: Disconnected wiring
Fix: Repair or replace stator coil, demagnetization of permanent magnet, clean brush contact and slip ring, repair or replace brush, or repair or replace sub coil
Output voltage is more than S.T.D. voltage by 30%
Cause: Defective AVR
Fix: Replace
Output voltage OV
Fix: Set the switch to the desired AC or DC position
Fluctuation of engine revolution is abnormal
Cause: Disconnected or punctured AVR capacitor, faulty brush contact, excessive initial current, low engine output, faulty engine governor
Fix: Replace capacitor, check for wear, wear amount, and contamination of contacting surface of brush and clean if necessary, repair or replace

Compiled from service & troubleshooting documentation across every generator set that uses the GN550-DG-A3.

Maintenance schedule

Item	Spec	Part #	Interval
Air filter	foam wrapper and cartridge-type element; check and clean	—	25 hr
Fuel filter	clean	—
Oil	API type SE, SF class engine oil	—	50 hr
Spark plug	gap 0.6-0.7 mm (GN550/GN1850); 0.9-1.0 mm (GN2500)	—	50 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
Engine oil	Change	50 hr		First service — First oil change after 10 hours operation
Air cleaner element	Replace		12 mo	Every six cleanings or every year

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	Crankshaft side clearance	0.02-0.1	mm	reference; allowable limit 0.2 mm
Clearance	Cylinder bore	42.000-42.025	mm	reference; allowable limit 42.2 mm
Clearance	Cylinder bore	60.00-60.02	mm	reference; allowable limit 60.12 mm
Clearance	Cylinder bore	67.000-67.025	mm	reference; allowable limit 67.2 mm
Clearance	Cylinder bore	71.98-72.00	mm	reference; allowable limit 72.2 mm
Clearance	Cylinder bore	73.00-73.02	mm	reference; allowable limit 73.12 mm
Clearance	Cylinder head surface distortion allowable limit	0.4	mm	max; also 0.0157 in
Clearance	Gear backlash	0.023-0.128	mm	reference; allowable limit 0.2 mm
Clearance	Gear backlash	0.029-0.123	mm	reference; allowable limit 0.2 mm
Clearance	Gear backlash	0.03-0.12	mm	reference; allowable limit 0.2 mm
Clearance	Gear backlash	0.033-0.119	mm	reference; allowable limit 0.2 mm
Clearance	Gear backlash	0.033-0.135	mm	reference; allowable limit 0.2 mm
Clearance	Piston pin to connecting rod small-end bore	0.010-0.025	mm	reference; allowable limit 0.1 mm
Clearance	Piston pin to connecting rod small-end bore	0.010-0.033	mm	reference; allowable limit 0.1 mm
Clearance	Piston pin to connecting rod small-end bore	0.015-0.030	mm	reference; allowable limit 0.1 mm
Clearance	Piston pin to connecting rod small-end bore	0.026-0.046	mm	reference; allowable limit 0.08 mm
Clearance	Piston ring gap	0.15-0.35	mm	top/2nd ring; oil ring 0.15-0.35 mm; allowable limit 0.5 mm
Clearance	Piston ring gap	0.2-0.4	mm	top/2nd ring; oil ring 0.2-0.4 mm; allowable limit 0.9 mm
Clearance	Piston ring gap	0.25-0.45	mm	top/2nd ring; oil ring 0.2-0.4 mm; allowable limit 0.9 mm
Clearance	Valve guide clearance exhaust	0.050-0.095	mm	reference; allowable limit 0.1 mm
Clearance	Valve guide clearance intake	0.030-0.067	mm	reference; allowable limit 0.1 mm
Clearance	Valve seat surface width	1.0-1.3	mm	reference; allowable limit 1.5 mm
Clearance	Valve spring free length	30.8-31.3	mm	reference; allowable limit 30.5 mm
Clearance	Valve spring squareness allowable limit	1.5	mm	allowable limit
Gap	Spark plug gap	0.0236-0.0276	in	also 0.6-0.7 mm
Gap	Spark plug gap	0.0276	in	also 0.7 mm
Gap	Spark plug gap	0.0354-0.0394	in	also 0.9-1.0 mm
Gap	Spark plug gap	0.0394	in	also 1.0 mm
Resistance	Rotor field coil	13.9	ohm	K450[K400]
Resistance	Rotor field coil	45	ohm	±5%; K1400[K1200]
Resistance	Rotor field coil	54	ohm	±5%; K2100[K1800]
Resistance	Stator main coil	2.43	ohm	±5%; K450[K400]
Resistance	Stator sub coil	10.5	ohm	±5%; K450[K400]
Torque	Bracket front bolt	156.2-191.0	lbf-in	also 180-220 kgf-cm, 17.65-21.58 N-m
Torque	Connecting rod bolt	13.7-19.6	N-m	also 1.4-2.0 kgf-m, 10.1-14.5 ft-lbs
Torque	Connecting rod bolt	16.7-22.6	N-m	also 1.7-2.3 kgf-m, 12.3-16.6 ft-lbs
Torque	Connecting rod bolt	3.9-5.9	N-m	also 0.4-0.6 kgf-m, 2.9-4.4 ft-lbs
Torque	Connecting rod bolt	9.8-13.7	N-m	also 1.0-1.4 kgf-m, 7.2-10.1 ft-lbs
Torque	Crankcase 2 tightening bolt	13.7-19.6	N-m	also 1.4-2 kgf-m, 10.1-14.5 ft-lbs
Torque	Crankcase 2 tightening bolt	2.8-3	N-m	also 0.29-0.31 kgf-m, 2.1-2.3 ft-lbs
Torque	Crankcase 2 tightening bolt	7.8-12.7	N-m	also 0.8-1.3 kgf-m, 5.6-9.4 ft-lbs
Torque	Cylinder head bolt	19.6-29.4	N-m	also 2-3 kgf-m, 14.5-21.7 ft-lbs
Torque	Cylinder head bolt	34.3-39.2	N-m	also 3.5-4 kgf-m, 25.3-29.0 ft-lbs
Torque	Cylinder head bolt	34.3-46.1	N-m	also 3.5-4.7 kgf-m, 25.3-34.0 ft-lbs
Torque	Drain plug	19.6-29.4	N-m	also 2-3 kgf-m, 14.5-21.7 ft-lbs
Torque	Drain plug	6.9-9.8	N-m	also 0.7-1 kgf-m, 5.1-7.2 ft-lbs
Torque	Flywheel tightening nut	19.6-24.5	N-m	also 2-2.5 kgf-m, 14.5-18 ft-lbs
Torque	Flywheel tightening nut	29.4-44.1	N-m	also 3-4.5 kgf-m, 21.7-32.5 ft-lbs
Torque	Flywheel tightening nut	58.8-68.6	N-m	also 6-7 kgf-m, 43.4-50.6 ft-lbs
Torque	Flywheel tightening nut	63.7-73.5	N-m	also 6.5-7.5 kgf-m, 47.0-54.2 ft-lbs
Torque	Output terminal nut	16.5-21.7	lbf-in	also 19-25 kgf-cm, 1.86-2.45 N-m
Torque	Rotor center bolt	104.1-138.9	lbf-in	also 120-160 kgf-cm, 11.77-15.69 N-m
Torque	Rotor center bolt	138.9-182.3	lbf-in	also 160-210 kgf-cm, 15.69-20.59 N-m
Torque	Rotor set bolt	138.9-182.3	lbf-in	also 160-210 kgf-cm, 15.69-20.59 N-m
Torque	Rotor set bolt	277.7-381.9	lbf-in	also 320-440 kgf-cm, 31.38-43.15 N-m
Torque	Spark plug	9.8-24.5	N-m	also 1-2.5 kgf-m, 7.2-18.1 ft-lbs
Torque	Stator thru bolt	52.1-78.1	lbf-in	also 60-90 kgf-cm, 5.88-8.83 N-m
Valve clearance	Valve clearance	0.07-0.13	mm	also 0.0028-0.0051 in
Valve clearance	Valve clearance	0.08-0.14	mm	also 0.0031-0.0055 in
Valve clearance	Valve clearance	0.08-0.15	mm	also 0.0035-0.0059 in

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
Engine oil	10W30	API type SE, SF class engine oil	below -10°C	below 14°F (-10°C)
Engine oil	SAE #20	API type SE, SF class engine oil	-10°C to 15°C	below 59°F (+15°C)
Engine oil	SAE #30	API type SE, SF class engine oil	above 15°C	above 59°F (+15°C)
Fuel	Regular automobile gasoline

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 Pilot Screw Opening Degree adjustment

Tools: screwdriver

Tighten pilot screw completely
Loosen according to reference value

Checking Valve Clearance adjustment

Tools: feeler gauge

Set piston at top dead center
Measure clearance with feeler gauge
If clearance is under reference value, grind valve stem to adjust

Checking Ignition Plug Gap maintenance

Tools: feeler gauge

Remove carbon
Measure clearance with feeler gauge
If clearance is out of reference value, readjust

Draining Engine Oil maintenance

Tools: wrench

Remove dipstick
Remove drain plug
Drain engine oil

Removing Air Cleaner (K1400/K2100/K3000/K3500) maintenance

Loosen air cleaner cover
Take out air cleaner element
Remove foam wrapper and wash in detergent and water
Dry thoroughly
Re-oil foam wrapper and squeeze out excess oil
Shake and tap cartridge element to remove dust
Install new element if still dirty
Re-install element and cover

Removing Air Cleaner (K450/K1000/K400/K800) maintenance

Tools: screwdriver

Remove air cleaner cover fixtures
Remove cover, element, and plate
Remove two air cleaner body tightening nuts
Remove air cleaner body

Removing Flywheel repair

⚠ Do not damage fins

Tools: air-cooled engine flywheel puller

Remove flywheel tightening nut
Remove flywheel
Remove woodruff key

Removing Fuel Tank and Fuel Filter repair

⚠ Gasoline fire hazard

Tools: screwdriver, wrench

Close fuel filter cock
Disconnect fuel pipe at carburetor side
Loosen fuel filter tightening bolt
Remove fuel filter from tank body
Remove four fuel tank tightening bolts
Remove fuel tank with filter connected

Removing Piston repair

⚠ Be careful of flywheel side direction and mark on connecting rod

Tools: wrench

Extend bent portion of rod bolt washer
Remove connecting rod bolt
Remove cap at large end of connecting rod
Pull out piston to cylinder head side

Removing Spark Plug, Cylinder Head and Head Gasket repair

⚠ Check assembling direction of gasket

Tools: wrench

Remove spark plug
Remove cylinder head
Remove head gasket

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

Which generators use the GN550-DG-A3 engine?

The GN550-DG-A3 powers 1 generator set(s), including Cummins/Onan K400.

How often should you change the oil in the GN550-DG-A3?

The GN550-DG-A3 oil change interval is every 50 hours.

What is a common problem with the GN550-DG-A3 engine?

A commonly reported issue on generators using the GN550-DG-A3 is: Only slight output voltage is delivered (3 ~ 6V). Cause: Worn brush or faulty contact surface of slip ring. Fix: Clean brush contact and slip ring, or replace brush.