Home›Engines›Generac OHV GA-420

Generac OHV GA-420 Engine

The Generac OHV GA-420 is a 0.42 L engine rated at 3600 rpm. It powers generator sets from Generac, including the PowerPact 5.6 kVA 50 Hz. It holds 1.1 L (0.3 gal) of oil.

Also known as: OHV GA-420, Generac OHV GA-420

0.42 L

Displacement

3600 rpm

Rated speed

1.1 L

Oil capacity

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

Engine specifications

Oil capacity	1.1 L
Displacement	0.42 L
Rated speed	3600 rpm

Generator sets powered by this engine

Generac PowerPact 5.6 kVA 50 Hz

How to read your Generac engine serial & model number →

Common problems

Voltage and frequency drop excessively when loads are applied
Cause: Overload condition; shorted condition in a connected load or in one of the load circuits; stator AC power windings faulty; engine condition poor
Fix: Reduce loads to unit's rated capacity; look for a shorted condition in a connected load or in one of the load circuits and repair or replace; check stator AC power windings; go to Problem 23 – Engine Starts Hard and Runs Rough/Lacks Power
Generator produces zero voltage or residual voltage
Cause: Main circuit breaker set to OFF or open, or has failed; fuses blown; brushes and slip rings faulty; rotor and rotor circuit resistance incorrect; stator faulty; voltage regulator faulty
Fix: Reset breaker to ON or replace if bad; repair or replace fuses; check brushes and slip rings; perform resistance check of rotor and rotor circuit; test stator; replace voltage regulator; replace rotor only; replace stator only; replace rotor and stator
Generator produces low voltage at no-load
Cause: Voltage regulator adjustment incorrect; engine governor adjustment incorrect; rotor and rotor circuit resistance incorrect; stator faulty
Fix: Adjust voltage regulator; adjust engine governor; perform resistance check of rotor and rotor circuit; test stator; replace rotor only; replace rotor and stator
Generator produces high voltage at no-load
Cause: Voltage regulator adjustment incorrect; engine governor adjustment incorrect; defective voltage regulator
Fix: Adjust voltage regulator; check and adjust engine governor; replace defective voltage regulator
Blown T1 fuse T1
Unit Starts and Transfer Occurs When Utility Power Is On Problem 14
Fix: Test 41 – Check Utility Sensing Voltage at Controller; Test 38 – Check N1 & N2 Voltage; Test 39 – Check Utility Sense Voltage; Test 32 – Check Fuse F1 & F2; replace controller; correct utility source voltage; replace; go to Problem 7; repair or replace wiring; repair or replace wire N1A/N2A between N1/N2 lugs and fuse holder; repair N1/N2 open wiring between transfer switch and generator; check meter settings and functionality
Shutdown Alarm/Fault Occurred — Overspeed Problem 24
Fix: Test 13 – Check and Adjust Engine Governor; repair linkage if binding; check throttle operation
Shutdown Alarm/Fault Occurred — Overcrank Problem 24
Fix: Test 64 – Check for Ignition Spark; Test 67 – Check Ignition Magneto; Test 79 – Check Shutdown Wire; repair or replace shorted wire 18 or controller; refer to engine service manual
Shutdown Alarm/Fault Occurred — No RPM Sense Problem 24
Fix: Test 71 – Check Wire 18 Continuity; Test 12 – Check AC Output Frequency; repair or replace; proceed to Problem 22; proceed to Problem 27
Shutdown Alarm/Fault Occurred — Low Oil PowerPact Problem 24
Fix: Test 68B – Check Oil Level Switch and Wire 86
Shutdown Alarm/Fault Occurred — Low Oil CorePower Problem 24
Fix: Test 68A – Check Oil Pressure Switch and Wire 86
Shutdown Alarm/Fault Occurred — Low Battery Problem 24
Fix: Go to Problem 21
Shutdown Alarm/Fault Occurred — High Temp Problem 24
Fix: Test 69 – Check High Oil Temperature Switch; check installation for proper airflow or replace defective switch
No Battery Charge — no battery supply voltage Problem 27
Fix: Test 74 – Check Battery Charger Supply Voltage; Test 75 – Check Battery Charger Output Voltage; Test 78 – Check Wire 0/15B; repair or replace; replace charger
Load Management Module (SMM) LED is ON, Load Not Powered SMM Problem 2
Cause: Generator was overloaded, shed occurred and power applied to SMM; this will also occur if utility power was just applied (except if transferring from gen to utility)
Fix: Test 37 – Check Voltage at Contactor

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

Service intervals

Item	Action	Hours	Months	Notes
Oil level	Check	24 hr		CorePower; monthly or 24 hours of continuous operation
Air cleaner	Clean	50 hr	3 mo	PowerPact; 3 months or 50 hours
Oil	Change	100 hr	12 mo	First service — PowerPact; change after first 20 hours or 1 month, then 100 hours or 6 months
Oil filter	Change	100 hr	12 mo	First service — CorePower; change after first 8 hours, then every 100 hours or 1 year
Spark plug	Inspect	100 hr	6 mo	PowerPact; 6 months or 100 hours
Complete tune-up	Other	200 hr	12 mo	CorePower; to be completed by a dealer
Spark plug	Replace	200 hr	12 mo	CorePower; 1 year or 200 hours
Air cleaner	Replace	300 hr	12 mo	PowerPact; 1 year or 300 hours
Spark plug	Change	300 hr	12 mo	PowerPact; 1 year or 300 hours
Valve clearance	Check	300 hr	12 mo	First service — PowerPact; check after first 20 hours, then every 300 hours or 1 year
Battery - remove corrosion, ensure dryness	Clean		12 mo	PowerPact; yearly
Battery charge state	Check		12 mo	PowerPact; yearly
Battery electrolyte level	Check		6 mo	CorePower; every 6 months
Battery electrolyte level (unsealed batteries only)	Check		6 mo	PowerPact; every 6 months
Battery terminals - clean and tighten	Clean		12 mo	PowerPact; yearly
Fuel lines and connections	Inspect		1 mo	CorePower; monthly
Vibration, Noise, Leakage	Inspect		1 mo	PowerPact; monthly
Vibration, Noise, Leakage, Temperature	Inspect		1 mo	CorePower; 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
Gap	Spark plug gap	0.76 mm (0.030 inch)	mm
Pressure	Cylinder leak down tester regulated pressure	80	PSI	90 PSI air source
Pressure	Fuel pressure - LP gas - inlet side of fuel solenoid	10-12	inches water column
Pressure	Fuel pressure - natural gas - inlet side of fuel solenoid	5-7	inches water column
Pressure	Minimum allowable compression pressure	60	PSI	cold engine
Pressure	Normal oil pressure	35-40	psi	engine running
Pressure	Oil pressure - shut engine down immediately if below	4.5	psi
Pressure	Oil pressure switch rating (single cylinder)	10	psi
Resistance	Choke solenoid (component table)	4	ohms
Resistance	Choke solenoid coil resistance	~3.7	ohms
Resistance	Fuel solenoid FS1 nominal resistance	14-16	ohms
Resistance	Main fuel solenoid	16	ohms
Resistance	Rotor resistance - CorePower	40 +/-20	ohms
Resistance	Rotor resistance - PowerPact	50 +/-20	ohms
Resistance	Starter contactor	8	ohms
Resistance	Stator DPE winding Blue (2)/Blue (6) - PowerPact	1.85	ohms
Resistance	Stator DPE winding Blue/Blue - CorePower	1.158	ohms
Resistance	Stator power winding 11/22 - PowerPact 50 Hz	0.36	ohms
Resistance	Stator power winding 11/22 - PowerPact 60 Hz	0.24	ohms
Resistance	Stator power winding 33/44 - PowerPact 50 Hz	0.36	ohms
Resistance	Stator power winding 33/44 - PowerPact 60 Hz	0.24	ohms
Resistance	Stator power winding Blue/Black - CorePower	0.346	ohms
Resistance	Stator power winding White/Black - CorePower	0.173	ohms
Resistance	Stator power winding White/Blue - CorePower	0.173	ohms
Resistance	Stator sensing winding Green/White - CorePower	0.064	ohms
Resistance	Stator sensing winding White (S1)/Green (S2) - PowerPact	0.024	ohms
Resistance	Transfer relay	115	ohms
Speed	No-load speed - 50 Hz	3120	RPM	52 Hz
Speed	No-load speed - 60 Hz	3750	RPM	62.5 Hz
Speed	Over speed shutdown - 50 Hz	3600	RPM	for three (3) seconds, or 3750 RPM immediately
Speed	Over speed shutdown - 60 Hz	4320	RPM	for three (3) seconds, or 4500 RPM immediately
Temperature	High oil temperature shutdown	124 C (255 F)	C
Temperature	High oil temperature switch - contacts close at	293	F
Temperature	High oil temperature switch test range	283-305 F (139-151 C)	F
Torque	3/8-16 screw to mounting foot	5-8	ft-lbs
Torque	Governor lever clamp bolt - CorePower	70	in-lbs
Torque	Governor lever clamp bolt - CorePower	8	Nm
Torque	Governor pinch bolt nut - PowerPact	62	in-lbs
Torque	M10 x 1.25 engine to vibration isolator	15-20	ft-lbs
Torque	M3 x 0.5 screw into aluminum	8-10	in-lbs
Torque	M3 x 0.5 taptite screw into extruded hole	8-18	in-lbs
Torque	M5 x 0.5 screw into aluminum	25-35	in-lbs
Torque	M5 x 0.8 screw on band clamp	7.5-9	ft-lbs
Torque	M5 x 0.8 taptite screw into extruded hole	25-50	in-lbs
Torque	M6 x 1.0 nyloc nut on dead front plate	40-50	in-lbs
Torque	M6 x 1.0 screw flange nuts - airbox to cylinder head	7-8	ft-lbs
Torque	M6 x 1.0 screw into aluminum	50-60	in-lbs
Torque	M6 x 1.0 screw on band clamp	14-15	ft-lbs
Torque	M6 x 1.0 taptite screw into extruded hole	50-96	in-lbs
Torque	M8 x 1.0 nuts - exhaust to cylinder head	20-22	ft-lbs
Torque	M8 x 1.25 taptite screw into extruded hole	15-20	ft-lbs
Torque	M8 x 1.25 vibration isolator to base	20-22	ft-lbs
Torque	Rocker arm jam nut	70 to 106	in-lbs
Torque	Rotor bolt - CorePower	30	ft-lbs
Torque	Rotor bolt - PowerPact	27-33	ft-lbs
Torque	Stator bolts - CorePower	6	ft-lbs
Torque	Stator bolts - PowerPact	72	in-lbs
Valve clearance	Exhaust valve - CorePower	0.007-0.009 in (0.18-0.22 mm)	in	cold
Valve clearance	Exhaust valve - PowerPact	0.002-0.004 in (0.05-0.1 mm)	in	cold
Valve clearance	Intake valve - CorePower	0.005-0.007 in (0.13-0.17 mm)	in	cold

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	Synthetic SAE 5W-30	API Service Class SJ, SL or better		for all temperature ranges; do not use synthetic until 50 hours of operation
Engine oil	SAE 10W-30	API Service Class SJ, SL or better	-23°C to 4°C	between 40 and -10 F (4 and -23 C)
Engine oil	SAE 30	API Service Class SJ, SL or better	above 0°C	above 32 F (0 C); do not use special additives
Fuel	LP vapor	at least 2,520 BTU per cubic foot		vapor withdrawal system only; fuel pressure must never drop below 10 inches water column
Fuel	Natural gas	at least 1,000 BTU per cubic foot		fuel pressure must never drop below 5 inches water column

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

Procedures

Test 13 - Check and Adjust Engine Governor (CorePower) adjustment

Tools: 13 mm wrench, frequency meter

Cycle throttle to confirm throttle rod and anti-lash spring move freely.
Loosen the governor clamp bolt (13 mm).
Hold governor lever wide open; rotate governor shaft clockwise fully.
Tighten governor lever clamp bolt to 70 in-lbs (8 Nm).
Connect a frequency meter across the AC output leads (MLCB).
Start the generator and warm up at no-load.
Turn the adjust nut to obtain a frequency reading of 62.5 Hz.

Test 70 - Check and Adjust Valves adjustment

Tools: feeler gauge, socket, wrench

Ensure the engine is cool before checking.
Remove spark plug wire and position it away from the plug.
Remove the spark plug.
Rotate the engine clockwise until piston is at TDC compression stroke.
Remove the four screws attaching the valve cover.
Loosen rocker jam nut; set clearance with a feeler gauge.
CorePower: intake 0.005-0.007 in; exhaust 0.007-0.009 in.
PowerPact: intake and exhaust 0.002-0.004 in.
Tighten jam nut to 70 to 106 in-lbs; recheck clearance; install new gasket.

Check Compression diagnostic

Tools: compression gauge

Remove the spark plug.
Insert a compression gauge into the cylinder.
Crank the engine until there is no further increase in pressure.
Record the highest reading obtained.
Minimum allowable compression pressure for a cold engine is 60 PSI.

Test 1 - Check Main Circuit Breaker diagnostic

Tools: Volt-Ohm-Meter

Set VOM to R x 1 scale and zero the meter.
With generator shut down, disconnect all wires from breaker terminals.
Connect probes to Wire 11 (Blue) terminal and the E1 terminal.
Set breaker Closed; VOM should read CONTINUITY.
Set breaker Open; VOM should indicate INFINITY.
Repeat with probes across Wire 44 (Black) and the E2 terminal.

Test 6 - Resistance Check of Rotor and Rotor Circuit diagnostic

Tools: Volt-Ohm-Meter

Disconnect the Red (Wire 4) and White (Wire 1) wires from the regulator.
Set a VOM to measure resistance.
Measure across the brush wires and record the resistance.
CorePower: approximately 40 ohms +/-20. PowerPact: approximately 50 ohms +/-20.

Reconfigure the Fuel System maintenance

Tools: needle nose pliers

Locate fuel throttle assembly mounted to engine intake.
Remove hose clamp and hose from throttle assembly.
Remove Natural Gas (larger ID) fuel jet from fuel inlet.
Obtain the Propane fuel jet (smaller ID) supplied loose.
Verify the O-ring is installed in the fuel jet groove.
Insert the Propane fuel jet into the end of the fuel inlet.
Reinstall hose and clamp onto fuel inlet and secure.
Verify the hose has not been kinked in any way.

Before Starting operation

⚠ Do not fill oil above the FULL mark.

Ensure the generator is OFF.
Set the generator main circuit breaker to OFF (or OPEN).
Turn off all breakers that will be powered by the generator.
Check crankcase oil level; fill to dipstick FULL mark.
Check fuel supply; purge and leak test lines; open all fuel shutoff valves.

Generator Activation operation

Locate and record the generator serial number.
Contact Generac to obtain your activation code.
Hold the OFF button for 3 seconds; all LEDs flash twice.
Enter the 6-press code using AUTO, OFF and SET EXERCISE within 20 seconds.
If incorrect, AUTO/OFF/MANUAL flash 3 times; return to Step 3.
If correct, all LEDs scroll bottom to top 5 times.

Manual Start and Transfer to Standby operation

⚠ Engine will crank and start!

Set the controller switch to OFF mode.
Set the generator main line circuit breaker to Open.
Locate a means of Utility disconnect and set it to OFF.
Manually actuate the breaker to Standby in the transfer switch.
Set the controller switch to MANUAL mode; engine cranks and starts.
Warm up 1-2 minutes; set the generator MLCB to Closed.

Retransfer to Utility and Manual Shutdown operation

Set the generator MLCB to the OPEN position.
Allow the generator to run at no-load several minutes to cool down.
Set the generator controller to OFF mode.
Locate a means of Utility disconnect and set it to OFF.
Manually actuate the breaker in the transfer switch to Utility.
Restore Utility voltage to the transfer switch.
Set the generator controller to AUTO mode.

Select Automatic Operation operation

Ensure transfer mechanism is in the Utility position.
CLOSE the Utility source main line circuit breaker.
Verify Utility voltage at terminals N1 and N2.
Actuate the generator main line circuit breaker to Closed.
Set the generator controller to the AUTO mode.

Shut Generator Down While Under Load operation

⚠ If turning the unit off for longer than 24 hours, remove the F1 fuse from the generator controller.

Turn the main utility disconnect OFF.
Turn the main line circuit breaker (MLCB) on the generator to OFF (OPEN).
Turn the generator OFF.

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 Generac OHV GA-420?

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

What is the displacement of the Generac OHV GA-420?

The Generac OHV GA-420 has a displacement of 0.42 liters.

Which generators use the Generac OHV GA-420 engine?

The Generac OHV GA-420 powers 1 generator set(s), including Generac PowerPact 5.6 kVA 50 Hz.

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

A commonly reported issue on generators using the Generac OHV GA-420 is: Voltage and frequency drop excessively when loads are applied. Cause: Overload condition; shorted condition in a connected load or in one of the load circuits; stator AC power windings faulty; engine condition poor. Fix: Reduce loads to unit's rated capacity; look for a shorted condition in a connected load or in one of the load circuits and repair or replace; check stator AC power windings; go to Problem 23 – Engine Starts Hard and Runs Rough/Lacks Power.