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Kohler CH20 4-Cycle Engine

Name: Kohler CH20 4-Cycle Engine
Brand: Kohler

The Kohler CH20 4-Cycle is a 0.62 L 2-cylinder natural gas or lp vapor engine rated at 3600 rpm. It powers generator sets from Kohler, including the 8.5RES.

Also known as: Kohler CH20 4-Cycle

0.624 L

Displacement

Cylinders

3600 rpm

Rated speed

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

Engine specifications

Displacement	0.624 L
Cylinders	2
Aspiration	Natural Gas or LP Vapor
Rated speed	3600 rpm

Generator sets powered by this engine

Kohler 8.5RES

How to read your Kohler engine serial & model number →

Common problems

Undervoltage shutdown UU
Cause: Shutdown occurs if the voltage falls below 80% of the nominal system voltage for more than 10 seconds.
Fix: Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues.
Underfrequency shutdown UF
Cause: Shutdown occurs if the governed frequency falls below 54 Hz for more than 5 seconds. Shutdown also occurs if the governed frequency falls below 56.5 Hz for more than 60 seconds. This function becomes active 10 seconds after engine start. (10 second inhibit).
Fix: Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues.
The generator set does not crank.
Cause: Battery weak or dead, Battery charger fuse blown, Battery connections reversed or poor, Controller fuse (F3) blown, Relay interface board fuse (F2) blown
Fix: Check power to the battery charger. Recharge or replace the battery. Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly. Check the connections. Replace the fuse. Contact an authorized distributor/dealer for service if fuse blows repeatedly.
The generator set cranks but does not start, starts hard, lacks power, or operates erratically.
Cause: Air cleaner clogged
Fix: Clean and/or replace the air cleaner. Battery weak or dead Check power to the battery charger. Recharge or replace the battery. Battery connection poor Clean and tighten the battery connections. Spark plug wire connection loose Check the spark plug wires. Low oil pressure shutdown Check the oil level. Fuel pressure insufficient Check the fuel supply and valves. Engine malfunction Contact an authorized distributor/dealer.
The generator set also shuts down on OC if no engine rotation is sensed during cranking. Shuts down 3 seconds after the fault is detected. Locked rotor
Stops suddenly
Cause: Fault shutdown
Fix: Check for a fault shutdown code on the controller’s LED display. Correct the fault and then move the generator set master switch to OFF/RESET to reset the controller.
Stator problem
Fix: Check voltage and continuity.
Shutdown occurs when the governed frequency falls 1 Hz below the system’s frequency setpoint for more than 1 second. UF
Fix: Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues.
Shutdown occurs when the governed frequency exceeds 110% of the system’s frequency setpoint for more than 1 second. This protective becomes active 30 seconds after engine start. OF
Fix: Contact an authorized distributor/dealer for service if problem continues.
Shutdown occurs if the voltage falls below 80% of the voltage regulator setpoint for more than 1 second. This protective becomes active 30 seconds after engine start. UU
Fix: Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues.
Shutdown occurs if the voltage exceeds 120% of the voltage regulator setpoint for more than 1 second. OU
Fix: Contact an authorized distributor/dealer for service if problem continues.
Shutdown occurs if the engine speed exceeds 115% of the normal running speed for more than 1 second. OS
Fix: Contact an authorized distributor/dealer for service if problem continues.
Shutdown occurs if the engine coolant temperature exceeds the maximum temperature for more than 5 seconds. This protective becomes active after the engine reaches the crank disconnect speed. HE
Fix: Check for blocked air inlets and exhaust outlets.
Shutdown occurs if a low oil pressure condition exists 7 seconds after the engine has reached crank disconnect speed. LOP
Cause: Note: The low oil pressure shutdown does not protect against low oil level. Check the oil level at the engine. Check for leaks in the lubrication system.
Fix: Check the oil level and add oil if the level is low.
Shutdown occurs after 3 unsuccessful starting attempts. The crank cycle is set for three starting attempts of 15 seconds cranking and 15 seconds rest. The generator set also shuts down after 1 crank attempt if no speed signal is sensed. Shuts down 1 second after the fault is detected. OC
Cause: Check the fuel supply, spark plug, and battery. Check for loose connections.
Fix: Contact an authorized distributor/dealer for service if problem continues.

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler CH20 4-Cycle.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Air Cleaner		—	100 hr
Fuel filter	Fuel Filter		—
Oil filter	Oil Filter		—	200 hr
Battery	Battery		—
Belt	Belt		—
Coolant	Cooling System		—
Oil	Engine Oil	1.9 L (qt.)	—	100 hr
Spark plug	Spark Plug		—	300 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
Oil level	Check	8 hr		First service — Lubrication; 8 hours or before use
Air cleaner and precleaner	Clean	100 hr	12 mo	Yearly or 100 Hrs.; service more often in dusty areas
Air cleaner and precleaner (8.5/12RES)	Replace	100 hr	12 mo	Yearly or 100 hours; replace as necessary
Air cleaner and precleaner service	Clean	100 hr	12 mo	Yearly or 100 hr.; service more frequently in dusty areas
Air cleaner and precleaner service	Replace	100 hr	12 mo
Air cleaner and precleaner service (8.5/12 kW)	Replace	100 hr		Yearly or 100 hours; service more frequently under dusty/dirty conditions
Air cleaner service	Replace	100 hr	12 mo	Engine and Mounting; Yearly or 100 hours; replace as necessary (R)
Change oil	Replace	100 hr	12 mo	Yearly or 100 hr.
Crankcase oil	Change	100 hr	12 mo	Yearly or 100 Hrs.
Engine oil	Change	100 hr	12 mo	Lubrication; Yearly or 100 hours
Oil cooler	Clean	100 hr	12 mo	Yearly or 100 hours; 17/18 kW models
Oil cooler	Inspect	100 hr		Yearly or 100 hours (17/18 kW models)
Oil cooler (17/18RES)	Clean	100 hr	12 mo	Yearly or 100 hours; inspect and clean
Air cleaner service	Clean	150 hr		Yearly or hours shown; 17/18 kW models
Air cleaner service (17/18 kW)	Replace	150 hr		Yearly or 150/300 hours
Change oil	Change	150 hr	12 mo	Yearly or 150 hours (17/18 kW models)
Engine oil (17/18RES)	Change	150 hr	12 mo	Yearly or 150 hours
Oil	Change	150 hr		Yearly or 150 hours; 17/18 kW models
Oil filter (17/18RES)	Replace	150 hr	12 mo	Yearly or 150 hours
Spark plugs	Clean	150 hr		Yearly or hours shown; 17/18 kW models
Spark plugs (17/18 kW)	Replace	150 hr		Yearly or 150/300 hours
Oil filter	Replace	200 hr	12 mo	Yearly or 200 hours; 8.5/12 kW models
Oil filter(s)	Replace	200 hr	12 mo	Yearly or 200 Hrs.
Replace filter	Replace	200 hr	12 mo
Replace filter (oil filter)	Replace	200 hr		Yearly or 200 hours (8.5/12 kW models)
Replace filter(s)	Replace	200 hr	12 mo	Yearly or 200 hr.
Air cleaner service	Change	300 hr		Yearly or hours shown; 17/18 kW models
Spark plugs	Check	300 hr	12 mo	Yearly or 300 hours; 8.5/12 kW models
Spark plugs	Replace	500 hr	12 mo	Yearly or hours shown; 17/18 kW models
Spark plugs (8.5/12 kW)	Replace	300 hr		Yearly or 300 hours
Spark plugs (8.5/12RES)	Check	300 hr	12 mo	Yearly or 300 hours
Crankcase breather	Change	500 hr	12 mo	Lubrication; Yearly or 500 hours
Crankcase breather hose	Check	500 hr	12 mo	Yearly or 500 hours; 8.5/12 kW models
Crankcase breather hose	Clean	500 hr	12 mo
Crankcase breather hose	Other	500 hr	12 mo	Yearly or 500 hr.; follow engine manufacturer's maintenance manual
Replace spark plugs	Replace	500 hr
Replace stepper motor coupling and bushing	Replace	500 hr		authorized distributor/dealer only
Resistance readings of windings with insulation tester (Megger)	Test	500 hr	36 mo	3 yr.; with SCR assembly or rectifier and load leads disconnected
Stepper motor coupling and bushing	Replace	500 hr	36 mo	Engine and Mounting; 500 hours
Wire-cable insulation breakdown	Inspect	500 hr	36 mo	3 Years or 500 Hrs.

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	Magnetic pickup air gap	0.5	mm (0.020 in.)
Gap	Spark Plug Gap 12/17/18RES	0.76	mm (0.030 in.)
Gap	Spark Plug Gap 8.5kW	0.51	mm (0.020 in.)
Gap	Spark plug gap	0.51	mm (0.02 in.)
Gap	Spark plug gap	0.7--0.8	mm (0.028--0.030 in.)
Gap	Spark plug gap	0.76	mm (0.030 in.)
Gap	Spark plug gap	0.8--0.9	mm (0.03--0.04 in.)
Gap	Spark plug gap	0.89	mm (0.035 in.)
Gap	Spark plug gap	0.9--1.0	mm (0.036--0.04 in.)
Other	Battery electrolyte specific gravity (full charge)	1.260		electrolyte at 26.7 C (80 F)
Other	Battery specific gravity (charge threshold)	1.215		electrolyte at 26.7 C (80 F)
Other	Battery specific gravity variation (charge threshold)	0.01		cell-to-cell variation
Other	Brush length, new	19.05	mm (0.75 in.)	new
Other	Compression ratio	8.5:1
Other	Compression ratio	9.0:1
Other	Fuel system leak test pressure	6-8 ounces per square inch (10-14 inches water column)	oz/in²	LPG vapor or natural gas system
Other	Insulation resistance indicating good stator/rotor	500	kOhms (1/2 megohm) or higher
Other	Megohmmeter test voltage (stator/rotor to ground)	500	VDC
Other	No load and full load frequency tolerance	0.4	Hz	rated generator frequency
Other	Overfrequency shutdown	110	% of system frequency setpoint for more than 5 seconds	10 second inhibit after start
Other	Overfrequency shutdown threshold	110	% of system frequency setpoint	more than 5 seconds, active 10s after start
Other	Underfrequency shutdown	90	% of nominal system frequency for more than 5 seconds	10 second inhibit after start
Other	Underfrequency shutdown threshold	54	Hz	more than 5 seconds (or below 56.5 Hz for more than 60 seconds)
Pressure	Engine oil pressure	172--241	kPa (25--35 psi)
Pressure	Fuel regulator inlet gas pressure	7-11	in. (4-6 oz.)	at fuel regulator inlet
Pressure	Fuel supply pressure	1.7--2.7	kPa	(7-11 in. H2O)
Pressure	Fuel supply pressure at secondary regulator inlet	178--280	mm water column (7--11 in. H2O) or 1.7--2.7 kPa (4--6 oz./in.2)	generator set running at rated load
Pressure	Gas fuel system leak test pressure	6--8	oz/in2	(10-14 inches water column), soap and water solution
Pressure	LP supply pressure	1.7--2.7	kPa (7--11 in. water column)
Pressure	Low oil pressure shutdown	24.1	kPa ±13.8 kPa (3.5 psi ±1.5 psi)
Pressure	Low oil pressure shutdown	24.1 ±13.8	kPa	(3.5 psi ±1.5 psi)
Pressure	Natural gas supply pressure	1.2--2.7	kPa (5--11 in. water column)
Pressure	Secondary regulator maximum inlet pressure	2.7	kPa (6 oz./in.2) or 280 mm (11 in.) water column
Resistance	Brush resistance	0.1--0.2	ohms (without meter lead resistance)
Resistance	Coolant temperature sensor (CTS) resistance	180--200	ohms	at 100 C (212 F)
Resistance	Coolant temperature sensor (CTS) resistance	2100--2500	ohms	at 30 C (86 F)
Resistance	Coolant temperature sensor resistance at 100 C (212 F)	180--200	ohms	100 C
Resistance	Coolant temperature sensor resistance at 30 C (86 F)	2100--2500	ohms	30 C
Resistance	Magnetic pickup resistance across QCON1 and QCON2	1.3--1.9	kOhm
Resistance	Resistance through the brushes	0.1--0.2	ohms	without meter lead resistance
Resistance	Rotor resistance	4.0	ohms, cold	cold
Resistance	Rotor resistance	4.2	ohms, cold	cold
Resistance	Rotor resistance, cold	4.0	ohms	cold
Resistance	Starter relay coil resistance	5--7	ohms
Resistance	Stator resistance leads 1-2, 3-4	0.07	ohms, cold	cold
Resistance	Stator resistance leads 1-4, 2-5, 3-6, 7-10, 8-11, 9-12	0.18	ohms, cold	cold
Resistance	Stator resistance leads 11-44	0.14	ohms, cold	cold
Resistance	Stator resistance leads 55-66	0.15	ohms, cold	cold
Resistance	Stator resistance leads 55-66	0.70	ohms, cold	cold
Resistance	Stator resistance, leads 1-2, 3-4	0.07	ohms	cold
Resistance	Stator resistance, leads 11-44	0.14	ohms	cold
Resistance	Stator resistance, leads 55-66	0.70	ohms	cold
Resistance	Stepper motor coil resistance per half coil	38.5	ohms
Speed	Crank cycle	15	seconds crank and 15 seconds off, 3 attempts	starting
Speed	Crank cycle	15 seconds crank and 15 seconds off, 3 attempts	seconds
Speed	Cut-in frequency	47.5	Hz	50 Hz units
Speed	Cut-in frequency	57.5	Hz	60 Hz units
Speed	Cut-in frequency, 50 Hz	47.5	Hz	50 Hz models
Speed	Cut-in frequency, 60 Hz	57.5	Hz	60 Hz models
Speed	Engine speed, full load (mechanical governor)	3600	RPM (60 Hz)	full load

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 SG, SH, or SJ synthetic			Synthetic oil recommended
Engine oil	Synthetic oil, API Service Class SG or higher	API SG or higher		1.9 L (2.0 qt.)	8.5RES capacity with filter; see engine oil selection chart for viscosity (5W-20, 5W-30, 10W-30)
Engine oil	5W-20, 5W-30	API Service Class SG or higher, synthetic	-30°C to 10°C		Engine Oil Selection chart; use synthetic oil
Engine oil	10W-30	API Service Class SG or higher, synthetic	-20°C to 40°C		Engine Oil Selection chart; use synthetic oil
Engine oil	API Service Class SG, SH, or SJ synthetic oil	API	20°C to 4°C	1.9 L (2.0 qt.)	10W-30 for one range; 5W-20/5W-30 shown to -20C
Fuel		LP gas or natural gas			Minimum supply pressure 7--11 in. H2O (4--6 oz./in.2); multi-fuel system field convertible
Fuel	LP gas or natural gas				LP/natural gas minimum supply pressure 7--11 in. H2O (4--6 oz./in.2)
Fuel	LP vapor				Nominal fuel rating 2500 Btu/ft3 (93 MJ/m3); supply pressure 1.7--2.7 kPa (7-11 in. H2O); LP vapor conversion factors: 8.58 ft3 = 1 lb., 36.39 ft3 = 1 gal.
Fuel	LPG				Fuel supply pressure 1.7-2.7 kPa (7-11 in H2O); nominal fuel rating 2500 Btu/ft3 (93 MJ/m3); supply inlet 1/2 NPT
Fuel	Natural Gas				Fuel supply pressure 1.3-2.7 kPa (5-11 in H2O) for 8.5/12RES, 1.7-2.7 kPa (7-11 in H2O) for 18RES; nominal fuel rating 1000 Btu/ft3 (37 MJ/m3); supply inlet 1/2 NPT
Fuel	Natural gas				Nominal fuel rating 1000 Btu/ft3 (37 MJ/m3); supply inlet 1/2 NPT; supply pressure 1.7--2.7 kPa (7-11 in. H2O)
Fuel	Natural gas or propane (LP) vapor	Field-convertible multi-fuel; CARB emission certified			Clean-burning natural gas or propane (LP) vapor; air-cooled engine, no liquid coolant
Other	Bicarbonate of soda (baking soda) and water solution				Battery acid cleanup: 500 g (1 lb.) bicarbonate of soda to 4 L (1 gal.) water; also used to clean battery and cables
Other	Petroleum jelly, silicone grease, or other nonconductive grease				Coat battery terminals after reconnecting cables

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
AF	Auxiliary fault input shutdown	Shutdown initiated by pushing the emergency stop switch (TRES models only). Not used on RES models.	Shutdown	Check the position of the emergency stop button. (TRES models only)
CC	Crank cycle
CO-3		Fault displayed if the CO parameter is set incorrectly	Shutdown
CO-6		Fault displayed if the CO parameter is set incorrectly	Shutdown
HB	High battery voltage warning	Fault code is displayed if the engine starting battery voltage rises above 16 VDC for more than 30 seconds when the engine is running. Not operative during the engine crank cycle; does not inhibit engine starting. Clears when the battery voltage returns to an acceptable level.	Warning	Check the battery rating and condition; check battery charger operation.
HE	High engine temperature shutdown	Shutdown occurs if the engine coolant temperature exceeds the maximum temperature for more than 5 seconds. This protective feature becomes active after the engine reaches the crank disconnect speed.	Shutdown	Check for blocked air inlets and exhaust outlets.
LB	Low battery voltage warning	Fault code is displayed if the engine starting battery voltage falls below 11 VDC for more than 30 seconds when the engine is not running. Not operative during the engine crank cycle; does not inhibit engine starting. Clears when the battery voltage returns to an acceptable level.	Warning	Check the battery rating and condition; check battery charger operation; charge or replace battery.
LCL	Low coolant level	Not used on air-cooled models.	Shutdown
LOC	Loss of coolant	Not used on air-cooled models.	Shutdown
LOP	Low oil pressure shutdown	Shutdown occurs if low oil pressure exists for more than 5 seconds; active 30 seconds after crank disconnect speed. Does not protect against low oil level.	Shutdown	Check for leaks in the lubrication system. Check the oil level and add oil if the level is low.
OC	Overcrank shutdown	Shutdown occurs after 3 unsuccessful starting attempts. The crank cycle is set for three starting attempts of 15 seconds cranking and 15 seconds rest. The generator set also shuts down on OC if no engine rotation is sensed during cranking; shuts down 3 seconds after the fault is detected (locked rotor).	Shutdown	Check the fuel supply, spark plug, and battery. Check for loose connections. Contact an authorized distributor/dealer if the problem continues.
OF	Overfrequency shutdown	Shutdown when governed frequency exceeds 110% of system frequency setpoint for more than 5 seconds; active 10 seconds after engine start.	Shutdown	Contact an authorized distributor/dealer for service if the problem continues.
OS	Overspeed shutdown	Shutdown occurs if the engine speed exceeds 115% of the normal running speed for more than 1 second.	Shutdown	Contact an authorized distributor/dealer for service if the problem continues.
OU	Overvoltage shutdown	Shutdown occurs if voltage exceeds 120% of system nominal voltage for more than 2 seconds.	Shutdown	Contact an authorized distributor/dealer for service if the problem continues.
SCF0	Software Communication Fault 0	Indicates a software or communication problem within the controller.	Shutdown	Replace the controller.
UF	Underfrequency shutdown	Shutdown when governed frequency falls below 90% of nominal system frequency for more than 5 seconds; active 10 seconds after engine start. (ADC-RES: below 54 Hz.)	Shutdown	Reduce the load and restart the generator set; contact distributor/dealer if problem continues
UU	Undervoltage shutdown	Shutdown occurs if voltage falls below 80% of nominal system voltage for more than 10 seconds.	Shutdown	Reduce the load and restart the generator set; contact distributor/dealer if problem continues

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

Procedures

ADC-RES Controller Configuration (Cn setting) adjustment

⚠ The controller automatically exits configuration mode without saving changes after about 1 minute if no buttons are pressed.

Enter the configuration mode while the engine is not running by following the Figure 26 sequence.
Step through the parameters to the communication setting Cn parameter.
Use the up and down arrow buttons to change the Cn setting to Cn01, if necessary.
Press to SAVE CHANGES (YES) before exiting the configuration mode.
Move the generator set master switch to OFF/RESET.

Controller Configuration adjustment

⚠ Be sure to save the new settings immediately before exiting the configuration mode; changes are lost if the controller times out (about 1 minute).

Hold the Select button and move the master switch to RUN to enter configuration mode.
Press the down arrow key then the up arrow key 3 times to enter configuration mode (password).
Set the voltage/frequency parameter Uu for the model.
Set the unit configuration parameter Uc (marine, standby, mobile).
Set the engine type parameter Ec.
Press the up arrow at the Adnc display to enter advanced configuration mode.
Set the engine data input type Ed.
Set the battery voltage Bt (12 or 24 VDC).
Set the communications parameter Cn.
Enter save mode and save your settings before exiting.

Frequency Adjustment Procedure adjustment

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: frequency meter

Open the generator set line circuit breaker.
Attach a frequency meter to the AC output leads.
Start and run the generator set until normal operating temperature (at least 10 minutes).
Use the ADC controller to adjust the electronic governor speed (parameter 4P) for 60 Hz (or 50 Hz).
Check stability with no load; decrease gain (parameter 5P) until stable if speed hunts or surges.
Repeat steps 4 and 5 to obtain rated frequency and stable operation.
Save the settings.
Apply rated load and observe frequency; no load and full load frequencies should be within 0.4 Hz of rated.
Check for hunting and surging at full load; increase gain until engine hunts, then decrease in small steps.
Remove the load and observe frequency; repeat step 4 if frequency changed.

Fuel Conversion Procedure (Models with Fuel Block) adjustment

⚠ Explosive fuel vapors. Use extreme care when handling, storing, and using fuels.

Disable genset: master switch OFF, disconnect battery charger, disconnect battery negative lead first.
Turn off fuel supply.
Remove hose clamp and fuel hose from hose fitting in the fuel metering valve.
Remove hose fitting from the natural gas outlet port.
Remove plug from LP port; clean, apply pipe sealant, install plug into natural gas port.
Clean hose fitting, apply pipe sealant, install fitting into LP port.
Slide hose onto fitting and secure with clamp.
For 12 kW models: connect DSAI leads together for natural gas (disconnect for LP).
Connect and turn on new fuel supply; reconnect battery negative last; reconnect battery charger.
Start genset and check for leaks using a gas leak detector.

Fuel Conversion Procedure (natural gas to LP vapor) adjustment

⚠ Do not adjust the factory-sealed fuel-metering adjustments on the fuel block.

⚠ Explosive fuel vapors can cause severe injury or death.

⚠ Accidental starting can cause severe injury or death.

Tools: Gas leak detector

Place the master switch in OFF, disconnect battery charger power, disconnect battery (negative lead first), and turn off fuel supply.
Remove the hose clamp and fuel hose from the hose fitting in the fuel block.
Remove the hose fitting from the natural gas outlet port in the fuel block.
Remove the plug from the LP port, clean it, apply fresh pipe sealant, and install it into the natural gas outlet port.
Clean the hose fitting, apply fresh pipe sealant to the threads, and install it into the LP port.
Slide the hose onto the fitting and secure it with the clamp.
For 12RES only: connect the DSAM leads together for natural gas (disconnect for LP vapor).
Connect and turn on the new fuel supply; recheck the master switch is OFF.
Reconnect the battery (negative lead last) and reconnect battery charger power.
Start the generator set by moving the master switch to RUN and check for leaks with a gas leak detector.
Move the generator set master switch to the AUTO position.

Fuel Metering Valve Adjustment Procedure adjustment

⚠ Adjusting fuel metering valves on emission-certified gensets may void the emission certification. Only trained authorized technicians may adjust.

Tools: Digital voltmeter (DVM), UEGO oxygen sensor service kit GM29385, Load bank

Disable genset (master switch OFF, disconnect battery charger).
Remove oxygen sensor plug from exhaust manifold and install oxygen sensor.
Connect oxygen sensor to engine starting battery, control module, and voltmeter.
Reconnect battery charger, start genset, and run to normal operating temperature.
Apply rated load; measure oxygen sensor output voltage (potential to ground).
Adjust fuel metering valve to obtain specified oxygen sensor output.
Seal metering valve adjustment screws with thread sealant.
Remove load and cool genset 5-10 minutes; stop genset.
Disconnect battery negative lead first; allow exhaust to cool.
Remove oxygen sensor and reinstall exhaust plug with antiseize; reconnect battery negative lead last and battery charger.

Mechanical Governor Arm Adjustment Procedure adjustment

⚠ Accidental starting can cause severe injury or death.

Tools: Nail

Make sure throttle linkage is connected to governor arm and carburetor throttle lever.
Loosen the hex nut holding the governor lever to the cross shaft.
Move governor lever toward carburetor as far as it will go (wide open throttle) and hold.
Insert a nail into the hole in the cross shaft and rotate the shaft counterclockwise as far as it will turn; tighten hex nut and remove nail.

Output Voltage and Frequency Adjustment adjustment

⚠ The generator set must be running during these adjustments.

⚠ The engine speed (frequency) adjustment menus are not accessible on models with mechanical governors.

Tools: multimeter

Move the master switch to RUN; the engine starts and runtime hours display.
Hold the Select button about 5 seconds until the program version number displays.
Press the down arrow key then the up arrow key 3 times to enter adjustment mode.
1P: adjust voltage coarse in large increments (approximately 5-7 volts per step).
2P: adjust voltage fine in smaller increments (approximately 0.5-0.7 volts per step).
Adjust voltage stability (gain) coarse and fine.
3P: set volts/Hz (00=low, 09=high).
4P: adjust engine governor speed coarse and fine.
5P: adjust engine governor stability (gain) coarse and fine.
Enter SAVE mode and save settings before exiting the adjustment mode.

Voltage Adjustment Procedure adjustment

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: digital voltmeter, frequency meter

Connect a digital voltmeter from one side of the circuit breaker to the L0 terminal inside the controller assembly.
Start the generator set.
Enter the adjustment mode and increase or decrease voltage (parameter 1P) to the desired voltage.
Adjust the voltage gain (parameter 2P) until light flicker minimizes; save settings.
Check and readjust the voltage if necessary.
Set voltmeter to frequency; adjust engine governor speed (parameter 4P) to the cut-in frequency.
Set voltmeter to voltage; adjust volts/Hz (parameter 3P) until voltage begins to drop.
Set voltmeter to frequency; adjust engine governor speed (parameter 4P) to the operating frequency (50 or 60 Hz).
Readjust voltage gain (parameter 2P) until light flicker minimizes.
Check voltage; readjust voltage (parameter 1P) if necessary.
Save the settings.
Stop the generator set.

Governor System Operation Test Procedure diagnostic

⚠ Hazardous voltage. Operate the generator set only when all guards and electrical enclosures are in place.

Tools: voltmeter, feeler gauge

Verify carburetor throttle linkage is connected to the stepper motor.
Look for broken or loose wiring or plug connections if stepper motor moves erratically.
Check stepper motor operation at startup; note throttle positions.
If throttle moves fully open then steps to and stays fully closed, check the magnetic pickup.
Connect a voltmeter to the magnetic pickup leads; check for 1.75 volts AC minimum during cranking.
If below 1.75 VAC, verify magnetic pickup air gap is 0.5 mm (0.020 in.); adjust as needed.
After adjusting gap, recheck voltage; replace magnetic pickup if still below 1.75 VAC.
Disconnect magnetic pickup leads and open circuit breaker to test controller governing function.
Move throttle shaft/stepper motor fully counterclockwise (closed throttle).
Start the generator set; stepper motor should step clockwise to wide open throttle and remain there.
Place master switch in STOP; check stepper motor connections (leads 1A, 1B, 2A, 2B to P1-4, P1-5, P1-6, P1-7).
Check stepper motor coil resistance across pins 2 and 3 and across pins 1 and 4.

Network Bridge Diagnostics diagnostic

Check the network LEDs on the RJ45 connector for Ethernet network communication.
Check the STAT LED; if not lit, check connections and the engine starting battery.
Check the TX and RX LEDs for CAN data transmission and reception.
If neither the TX nor the RX LED flashes, check bridge power, connections, and settings.
If only one of the TX or RX LEDs flashes, check the connected devices on the generator set (CAN) side.

Resetting Controller after a Fault Shutdown diagnostic

⚠ Always identify and correct fault cause before resetting controller

Move master switch to OFF/RESET
Disconnect generator set from load using line circuit breaker or ATS
Identify and correct the cause of the fault shutdown
Start generator set by moving switch to RUN; test operate to verify shutdown cause corrected
Move master switch to OFF/RESET
Reconnect generator set to load using line circuit breaker or ATS
Move master switch to AUTO position for remote transfer switch or remote start/stop startup

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
		Remote start	Controller leads 3 and 4	Connect leads 3 and 4 from the ADC 2100 controller to the ATS engine start terminals or a remote start/stop switch.
	single phase	AC output leads to AC circuit breaker	L1/L2 (black)	Connect output leads going to the transfer switch to the AC circuit breaker load side; route through flexible conduit to circuit breaker box.
	single phase	Equipment ground	Green	Connect the green lead to the equipment ground terminal (labeled GRD).
	single phase	Neutral	L0 (white)	Connect the L0 white leads from the ATS and the main panel to the neutral terminal.
100 VAC	1	1Ph, 2W		Uu00; 60 Hz
100 VAC	1	1Ph, 3W		Uu00; 60 Hz
100/200 VAC	1	1Ph, 3W		Uu08; 60 Hz
110	Single (L0-L1)	Factory two-pole circuit breaker		50 Hz; not reconnectable
110	Single (L0-L2)	Factory two-pole circuit breaker		50 Hz; not reconnectable
110 VAC	1	1Ph, 2W		Uu05; 50 Hz
110 VAC	1	1Ph, 3W		Uu05; 50 Hz
110 volt	1	L0-L1		50 Hz; 3-wire configuration; 8.5/12RES not reconnectable
110 volt	1	L0-L2		50 Hz; 3-wire configuration; 8.5/12RES not reconnectable
110/190 VAC	3	Wye		Uu17; 50 Hz
110/220 VAC	1	1Ph, 3W		Uu07; 50 Hz
110/220 VAC	1	Dogleg		Uu07; 50 Hz
110/220 VAC	3	Delta		Uu15; 50 Hz
115 VAC	1	1Ph, 2W		Uu05; 50 Hz
115/200 VAC	3	Wye		Uu23; 50 Hz
115/230 VAC	1	1Ph, 3W		Uu02; 50 Hz
115/230 VAC	1	Dogleg		Uu06; 50 Hz
115/230 VAC	3	Delta		Uu14; 50 Hz
12		Engine starting battery	Positive (+) and negative (--)	12-volt engine electrical system, negative ground. Positive lead to starter solenoid; negative lead to ground terminal on or near starter motor.
120	Single (L0-L1)	Factory two-pole circuit breaker; 4 stator leads	1, 2, 3, 4 (output); 11, 44, 55, 66 (sensing/supply)	60 Hz, 110/220 and 120/240 V, 3-wire configuration; not reconnectable
120	Single (L0-L2)	Factory two-pole circuit breaker		60 Hz; not reconnectable
120 VAC		Utility Power terminals on field-connection terminal block		Utility power circuit must be backed up by the generator set
120 VAC	1	1Ph, 2W		Uu00; 60 Hz
120 VAC	1	1Ph, 3W		Uu00; 60 Hz
120 volt	1	L0-L1		60 Hz; 3-wire configuration; 8.5/12RES not reconnectable
120 volt	1	L0-L2		60 Hz; 3-wire configuration; 8.5/12RES not reconnectable

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 Kohler CH20 4-Cycle?

The Kohler CH20 4-Cycle has a displacement of 0.624 liters with 2 cylinders.

Which generators use the Kohler CH20 4-Cycle engine?

The Kohler CH20 4-Cycle powers 1 generator set(s), including Kohler 8.5RES.

How often should you change the oil in the Kohler CH20 4-Cycle?

The Kohler CH20 4-Cycle oil change interval is every 100 hours.

What is a common problem with the Kohler CH20 4-Cycle engine?

A commonly reported issue on generators using the Kohler CH20 4-Cycle is: Undervoltage shutdown. Cause: Shutdown occurs if the voltage falls below 80% of the nominal system voltage for more than 10 seconds.. Fix: Reduce the load and restart the generator set. Contact an authorized distributor/dealer for service if problem continues..