GA-420 Engine

The GA-420 is a 25.6 L 1-cylinder engine. It powers generator sets from Generac, including the 7 kW PowerPact and 7.5 kW PowerPact. It holds 1.1 L (0.3 gal) of oil.

Also known as: GA-420

25.6 L

Displacement

Cylinders

1.1 L

Oil capacity

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

Engine specifications

Oil capacity	1.1 L
Displacement	25.6 L
Cylinders	1

Generator sets powered by this engine

Generac 7 kW PowerPact Generac 7.5 kW PowerPact

Common problems

Unit consumes large amounts of oil.
Cause: 1. Engine overfilled with oil. 2. Engine breather defective. 3. Improper type or viscosity of oil. 4. Damaged gasket, seal or hose.
Fix: 1. Adjust oil to proper level. 2. * 3. See Engine Oil Requirements. 4. Check for oil leaks.
No transfer to standby after utility source failure.
Cause: 1. Main line circuit breaker is in the OFF (or OPEN) position. 2. Defective transfer switch coil. 3. Defective transfer relay. 4. Transfer relay circuit open. 5. Defective control logic board.
Fix: 1. Reset circuit breaker to ON (or CLOSED). 2. * 3. * 4. * 5. *
No AC output from generator.
Cause: 1. Main line circuit breaker is in the OFF (or OPEN) position. 2. Generator internal failure.
Fix: 1. Reset circuit breaker to ON (or CLOSED). 2. *
Generator is set to OFF, but the engine continues to run.
Cause: 1. Controller wired incorrectly 2. Defective control board.
Fix: 1. Repair wiring.* 2. Replace control panel*
Engine will not crank.
Cause: 1. Fuse blown. 2. Loose, corroded or defective battery cables. 3. Defective starter contact. 4. Defective starter motor. 5. Dead battery.
Fix: 1. Correct short circuit condition by replacing 7.5 Amp fuse in generator control panel. 2. Tighten, clean or replace as necessary.* 3. *See #2. 4. *See #2. 5. Charge or replace battery.
Engine starts hard and runs rough.
Cause: 1. Air cleaner plugged or damaged. 2. Defective spark plug(s). 3. Fuel pressure incorrect. 4. Fuel selector in wrong position.
Fix: 1. Check / replace air cleaner. 2. Clean, re-gap or replace plug(s). 3. Confirm fuel pressure to regulator is 10–12 in. water column (19-22 mm mercury) for LP, and 5–7 in. water column (9-13 mm mercury) for natural gas. 4. Turn fuel conversion valve to correct position.
Engine cranks but will not start.
Cause: 1. Out of fuel. 2. Defective fuel solenoid (FS). 3. Defective spark plug(s). 4. Valve clearance out of adjustment. 5. In cold weather condition.
Fix: 1. Replenish fuel / Turn on fuel valve. 2. * 3. Clean, re-gap or replace plug(s). 4. Reset valve clearance. 5. Install recommended cold weather kit.

Compiled from service & troubleshooting documentation across every generator set that uses the GA-420.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			0E9371A	50 hr	Amazon eBay $19.99
Fuel filter			—
Oil filter	Generac oil kits meet minimum API Service Class SJ, SL or better and include an air filter		—
Battery	Group U1, 12 Volts, 300 CCA minimum		—
Oil	SAE 30 above 32F(0C); SAE 10W-30 between 40 and -10F(4 and -23C); Synthetic SAE 5W-30 for all temp ranges; API SJ, SL or better	1.2 L (1.2 qt)	—	100 hr
Spark plug	Gap 0.030 in (0.76 mm); torque 20-22 ft-lb (27-30 Nm)		0J5584	300 hr	eBay

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
Break-in maintenance (oil change, valve clearance, tune-up)	Other	20 hr		First service — 20-hour break-in interval
Oil, oil filter and air filter replacement	Replace	20 hr		First service — Recommended after the first 20 hours after installation
Valve Adjustment	Adjust	20 hr		First service — Recommended after the first 20 hours of operation
Oil level	Check	24 hr	1 mo	Monthly or 24 hours of continuous operation
Air cleaner	Clean	50 hr	3 mo	3 months / 50 hours - clean
Oil	Change	100 hr	6 mo	Severe duty: hot/dusty ambient (above 85F/29.4C) change every 3 months or 50 hours
Scheduled Maintenance	Other	100 hr	12 mo	1 Year / 100 Hour Maintenance Due indicated on control panel
Spark plug	Inspect	100 hr	6 mo	6 months or 100 hours - inspect
Air cleaner	Replace	300 hr	12 mo	1 year / 300 hours - replace
Spark plug	Change	300 hr	12 mo	1 year or 300 hours - change
Valve clearance	Check	300 hr	12 mo	Check first at 20 hours, then every 300 hours
Battery - check charge state	Check		12 mo	Yearly
Battery - remove corrosion, ensure dryness	Clean		12 mo	Yearly
Battery charge state	Check		12 mo	Yearly
Battery corrosion	Inspect		12 mo	Yearly; remove corrosion, ensure dryness
Battery electrolyte level (unsealed batteries only)	Check		6 mo	Every 6 months
Battery inspection and charge check	Check		12 mo	Recommended every year for the life of the battery
Battery terminals	Clean		12 mo	Clean and tighten yearly
Battery terminals - clean and tighten	Clean		12 mo	Yearly
Break-in Maintenance	Other			First service — Perform break-in maintenance when control panel indicates BREAK-IN MAINTENANCE DUE
Electrolyte level (unsealed batteries)	Check		6 mo	Every 6 months
Fuel lines and connections	Inspect		1 mo	Monthly; contact dealer if repair needed
General Condition - vibration, noise, leakage	Inspect		1 mo	Monthly; contact dealer if repair needed
Vibration, noise, leakage	Inspect		1 mo	Monthly

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	Spark Plug Gap	0.76	mm (0.030 in)	7 kW units
Gap	Spark plug gap	0.030	in (0.76 mm)
Pressure	Fuel pressure to regulator (LP)	10-12	in. water column (19-22 mm mercury)
Pressure	Fuel pressure to regulator (Natural Gas)	5-7	in. water column (9-13 mm mercury)
Pressure	LP Fuel Pressure to Regulator	10-12	in water column (19-22 mm mercury)	LP gas
Pressure	Natural Gas Fuel Pressure to Regulator	3.5-7	in water column (9-13 mm mercury)	Natural gas
Speed	Generator output frequency under load	240 volts, 60 Hz		under rated load
Torque	Rocker Arm Jam Nut	174	in-lb (19.68 N-m)
Torque	Rocker arm jam nut torque	174	in-lbs (19.68 Nm)
Torque	Spark Plug	20-22	ft/lb (27-30 Nm)
Torque	Spark plug torque	20-22	ft-lb (27-30 Nm)
Torque	Valve Cover Fasteners	35-62	in/lb (4-7 Nm)
Torque	Valve cover fasteners torque	35-62	in-lbs (4-7 Nm)	cross pattern
Valve clearance	Valve clearance	0.002-0.004	in (0.05-0.1 mm)	engine cool
Voltage	Generator output voltage at no load (E1-E2)	236–240	volts AC	at frequency 62–63 Hz, no load
Voltage	Generator output voltage, line-to-neutral (E1/E2-neutral)	118–120	volts AC
Voltage	Utility power source voltage, line-to-line (N1-N2)	240	volts AC	nominal
Voltage	Utility power source voltage, line-to-neutral (N1/N2-neutral)	120	volts AC	nominal, if wired with neutral

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	Synthetic SAE 5W-30	API SJ, SL or better		1.1 L (1.2 qt)	For all temperature ranges
Engine oil	SAE 10W-30	API SJ, SL or better	-23°C to 4°C	1.1 L (1.2 qt)	Between 40F and -10F (4C and -23C)
Engine oil	SAE 30 above 32F (0C); 10W-30 between 40F and -10F (4C and -23C); Synthetic 5W-30 for all temperature ranges (after 100 hours)	API SJ, SL or better	above -23°C	1.2 Qt (1.1 L)	No special additives
Engine oil	SAE 30	API SJ, SL or better	above 0°C	1.1 L (1.2 qt)	Above 32F (0C)
Fuel	LP Vapor, min. 2,500 BTU/ft3 (93.15 MJ/m3)				Required pressure 10–12 in H2O (19–22 mm HG); minimum tank 250 gal (946 L), or 1050 lb (476 kg) vertical tank
Fuel	Natural Gas, min. 1,000 BTU/ft3 (37.26 MJ/m3)				Required pressure 5–7 in. water column (9–13 mm mercury)
Fuel	Natural gas (min 1,000 Btu/cu ft / 37.26 MJ/m3) or LP gas vapor (min 2,500 Btu/cu ft / 93.15 MJ/m3); factory set to run on natural gas				Minimum LP tank size of 250 gallons (946 liters) recommended if converting from natural gas to LP

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 Year / 100 Hour Maintenance Due	Regular Maintenance Due	1 year / 100 hour maintenance due (solid)	Info	Perform scheduled maintenance, clear maintenance due light
BATTERY PROBLEM	Battery Problem Warning	Battery problem exists	Warning	Contact IASD
Break-in Maintenance Due	Break-in Maintenance Due	20 hour break-in maintenance due (flashing)	Info	Perform break-in maintenance, clear maintenance due light
CHARGER PROBLEM	Charger Warning	Charging problem exists	Warning	Contact IASD
HIGH TEMPERATURE	High Temperature Alarm	Temperature levels are excessive; unit shuts down during operation	Shutdown	Check ventilation around generator, intake, exhaust and rear; if no obstruction, contact IASD
LOW OIL PRESSURE	Low Oil Level Alarm	Unit will not start in AUTO with utility loss; oil level insufficient	Shutdown	Check oil level, add oil per Engine Oil Requirements; if correct, contact IASD
NO LEDs LIT	No Power / Fuse	Unit will not start in AUTO with utility loss; no LEDs lit	Shutdown	Check ATO 7.5 Amp fuse, replace with same type if bad; contact IASD if fuse is good
NOT ACTIVATED	Not Activated	Unit will not start in AUTO with utility loss; screen says unit not activated	Info	Refer to activation section in Installation Manual
OVERCRANK	Overcrank Alarm	Overcranking condition exists; unit will not start in AUTO with utility loss	Shutdown	Verify fuel line shutoff valve ON, clear alarm, attempt start in MANUAL; if fails, contact IASD
OVERSPEED/UNDERSPEED	Overspeed/Underspeed Alarm	Overspeed or underspeed condition exists	Shutdown	Contact IASD
RPM SENSE LOSS	RPM Sensor Alarm	Unit was running and shuts down; RPM sensor problem exists; attempts to restart	Shutdown	Clear alarm, remove household loads, put back in AUTO and restart; if not start, contact IASD
WIRING ERROR	Wiring Error	Wiring error detected; unit will not start in AUTO with utility loss	Shutdown	Contact IASD

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 Valve Clearance adjustment

Tools: 10mm wrench, feeler gauge, torque wrench

Cool engine before adjustment
Remove enclosure lid, fasteners, back panel
Remove spark plug wire and spark plug
Remove 4 screws attaching valve cover, discard gasket
Loosen rocker jam nut with 10mm wrench
Turn pivot ball stud while checking clearance with feeler gauge to 0.002-0.004 in (0.05-0.1 mm)
Hold pivot ball stud, tighten rocker arm jam nut to 174 in-lbs (19.68 Nm)
Recheck clearance
Install new valve cover gasket
Install valve cover, tighten fasteners in cross pattern to 35-62 in-lbs (4-7 Nm)
Install rubber plug into fan screen
Install spark plug and wire
Install back panel and enclosure top lid
Place generator in AUTO

Adjusting Valve Clearance adjustment

Tools: 13 mm Allen wrench, Feeler gauge

Ensure engine is at 60-80 F (16-27 C).
Remove enclosure lid and back panel if not already removed.
Ensure spark plug wire is removed and out of the way.
Remove the six screws attaching the valve cover.
Loosen the rocker jam nut; turn the pivot ball stud with a 13 mm Allen wrench while checking clearance with a feeler gauge to 0.002-0.004 in (0.05-0.1 mm).
Hold the pivot ball stud in place and tighten the rocker arm jam nut to 174 in-lb (19.68 N-m); recheck clearance.
Install new valve cover gasket, starting all six screws before tightening.
Install the valve cover; tighten fasteners to 35-62 in/lb (4-7 Nm).
Install the rubber plug into the fan screen.
Install the spark plug and attach the spark plug wire.
Install the back panel and enclosure top lid; tighten all fasteners securely.
Place the generator in AUTO.

Check Valve Clearance adjustment

Tools: feeler gauge, socket wrench

Cool engine before checking
Turn generator OFF
Remove enclosure lid fasteners, lid, and back panel
Remove spark plug wire and spark plug
Rotate flywheel nut clockwise to bring piston to TDC of compression stroke
Check clearance between rocker arm and valve stem with feeler gauge
If clearance is 0.002-0.004 in (0.05-0.1 mm), no adjustment needed

Battery Installation installation

⚠ Explosion hazard; connect positive cable first to avoid spark

⚠ Disconnect battery ground terminal before working on battery

Verify generator is turned OFF
Turn off utility power supply to transfer switch
Remove 7.5A fuse from generator control panel
Connect red battery cable (from starter contactor) to positive (+) post
Connect black battery cable (from frame ground) to negative (–) post
Install red battery post cover
Install battery bracket and screw
Install 7.5 Amp ATO fuse in control panel
Assemble battery access panel with 2 hex head screws
Assemble front door and top lid

Checking Gas Line Connections installation

Tools: Manometer

Remove top lid and rear panel
Check for leaks with non-corrosive gas leak detection fluid at all connection points
Close gas supply valve
Remove top gas pressure test port from regulator, install manometer
Open gas supply valve and verify pressure is within specified values
Close gas valve when completed
Reinstall rear access panel and top lid

Electrical Checks installation

⚠ High voltage present at transfer switch and terminals

Tools: AC voltmeter, Frequency meter

Verify generator OFF and main breaker OFF
Turn OFF all breakers/loads powered by generator
Turn on utility power to transfer switch
Check utility voltage across N1-N2 (240VAC nominal) and N1/N2-neutral (120VAC nominal)
Turn OFF utility power to transfer switch
Push MANUAL button, engine should crank and start
Let engine warm up 5 minutes, set main circuit breaker to ON
Check output voltage across E1-E2 (236-240V at 62-63Hz) and E1/E2-neutral (118-120V)
Set main breaker OFF, push generator OFF button

Fuel Conversion (NG to LP) installation

⚠ Connection of fuel source must be done by a qualified professional

Tools: 4mm and 6mm Allen wrenches, Needle nose pliers

Remove four 6mm Allen fasteners and lift top lid
Remove two 4mm Allen fasteners, lift and remove rear panel
Squeeze hose clamp and slide from fuel inlet
Remove hose from fuel inlet
Remove NG fuel jet from fuel inlet
Locate LP fuel jet (supplied, smaller ID than NG jet)
Insert LP fuel jet into end of fuel inlet
Reinstall hose on fuel inlet, secure with clamp
Verify hose is not kinked
Reinstall rear access panel and top lid

Generator Activation installation

Obtain activation code via www.generac.com or 1-888-9ACTIVATE using unit serial number
Hold OFF button for 3 seconds until all LEDs flash twice
Enter 6-press activation code sequence using AUTO/OFF/SET EXERCISE buttons within 20 seconds
If incorrect, AUTO/OFF/MANUAL buttons flash 3 times; retry
If correct, all LEDs scroll bottom to top 5 times and OFF button lights

Battery Maintenance maintenance

⚠ Remove 7.5 Amp fuse before working on battery

⚠ Wear eye protection and rubber gloves

Lift lid, remove front panel and battery access panel with generator shut down
Inspect battery posts and cables for tightness and corrosion, tighten/clean as necessary
Check battery fluid level of unsealed batteries, fill with distilled water only if necessary

Changing the Engine Air Cleaner maintenance

Remove top lid with generator shut down
Disengage wire clip and remove air cleaner access cover
Remove old air filter and discard
Clean air cleaner enclosure of dust/debris without letting debris fall into intake
Install new air filter
Install air cleaner cover and engage wire clip
Install enclosure top lid, tighten fasteners securely
Place generator in AUTO

Changing the Oil maintenance

⚠ Allow engine to cool before draining oil

Tools: hex head screwdriver

Start engine via MANUAL button, run until warmed up, then press OFF
Remove enclosure top lid and front panel
Remove battery access panel (2 hex head screws)
Disconnect battery and remove fuse
Pull oil drain hose free of retaining clip
Remove cap from hose, direct into container
Unscrew drain hose cap, drain oil (remove dipstick to drain faster)
Replace drain hose cap and secure with retaining clip
Refill engine with recommended oil
Connect battery, secure access panel, insert fuse, switch to MANUAL
Start engine, run 1 minute, check for leaks
Shutdown engine, check oil level, add as needed, do not overfill
Insert dipstick/fill cap
Press AUTO button
Dispose of used oil and filter at proper collection center

Checking Engine Oil Level maintenance

Turn OFF all associated loads via electrical panel main disconnect if running during outage
Turn generator main circuit breaker to OFF
Press control panel OFF button
Remove 7.5 Amp fuse from control panel
Remove enclosure top lid and front panel
Remove dipstick/fill cap and wipe dry
Insert dipstick without threading, remove again, verify level at H mark
Add oil if necessary to FULL mark
Turn main circuit breaker ON if running during outage
Install 7.5 Amp fuse
Press control panel AUTO button
Turn ON needed loads

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
		Transfer Control Signal Wire	WHITE #5	Terminal E, wire 23
12 VDC		Transfer Controls (+)	RED #4	Terminal D, wire 194
120VAC fused	1	T1 - Battery Charger	BLUE #3	Terminal B; must be connected to keep battery charged
240 VAC sensing	1	N1 & N2 - Utility Dropout/Pickup Sensing	YELLOW #1 & #2	Terminal A
DC		DC (–) Common Ground Wire	BLACK #3	Terminal C; required if paired with Generac Smart Power transfer switch

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 GA-420?

The GA-420 engine has an oil capacity of 1.1 liters.

What is the displacement of the GA-420?

The GA-420 has a displacement of 25.6 liters with 1 cylinders.

Which generators use the GA-420 engine?

The GA-420 powers 2 generator set(s), including Generac 7 kW PowerPact, Generac 7.5 kW PowerPact.

How often should you change the oil in the GA-420?

The GA-420 oil change interval is every 100 hours.

What is a common problem with the GA-420 engine?

A commonly reported issue on generators using the GA-420 is: Unit consumes large amounts of oil.. Cause: 1. Engine overfilled with oil. 2. Engine breather defective. 3. Improper type or viscosity of oil. 4. Damaged gasket, seal or hose.. Fix: 1. Adjust oil to proper level. 2. * 3. See Engine Oil Requirements. 4. Check for oil leaks..