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Kohler CH18-25 Engine

The Kohler CH18-25 is a 2-cylinder engine. It powers generator sets from Kohler, including the CH18.

Also known as: Kohler CH18-25

Part of the Kohler CH18 engine family — 2 variants share parts & fitment.

Cylinders

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

Engine specifications

Cylinders	2

Generator sets powered by this engine

Kohler CH18

How to read your Kohler engine serial & model number →

Common problems

Will Not Start
Cause: Improper Fuel, Dirty Fuel Line/System, Grass Screen, Overloaded
Fix: Clean or replace fuel filter; clean air cleaner element and precleaner; ensure proper battery condition.
MIL comes on
Fix: If the MIL comes on, or the engine becomes hard to start, runs roughly, or stalls at low idle speed, initial checks should be made in the following areas: - Make sure the fuel tank is filled with clean, fresh gasoline.
Engine troubles that appear to be fuel system related
Fix: Check the following areas before adjusting the carburetor: - Make sure the fuel tank is filled with clean, fresh gasoline. - Make sure the fuel tank cap vent is not blocked and that it is operating properly. - If the fuel tank is equipped with a shut-off valve, make sure it is open. - If the engine is equipped with an in-line fuel filter, make sure it is clean and unobstructed. Replace the filter if necessary. - Make sure fuel is reaching the carburetor. This includes checking the fuel lines and fuel pump for restrictions or faulty components, replace as necessary. - Make sure the air cleaner element is clean and all air cleaner element components are fastened securely.
Engine hard to start, runs roughly, or stalls at low idle speed
Fix: If after checking the items listed above, adjust or service the carburetor. There are no accessible mixture adjustment screws on the carburetor. The only setting which can be changed is the low idle speed. 1. Start the engine and run at half throttle for 5 to 10 minutes to warm up. The engine must be warm before making final settings (steps 2 and 3). 2. Low idle Speed Setting: Place the throttle control into the “idle” or “slow” position. Set the low idle speed to 7200 RPM (+ 75 RPM) by turning the low idle speed adjusting screw in or out. Check the speed using a tachometer. *NOTE: The actual low idle speed depends on the application - refer to equipment manufacturers recommendations. The standard low idle speed is 1200 RPM. 3. If proper operation is not restored after adjusting the low idle speed, carburetor servicing by an authorized Kohler Engine Service Dealer may be required.

Compiled from service & troubleshooting documentation across every generator set that uses the Kohler CH18-25.

Maintenance schedule

Item	Spec	Part #	Interval
Air filter	Service air cleaner element. Replace heavy-duty air cleaner element and check inner element.	—	500 hr
Fuel filter	EFI Engines: A special, high volume, high pressure filter with greater filtration capabilities and internal surface area is used. See Figure 15.	—
Oil filter	Change oil filter. Replace fuel filter (EFI engines).	—	200 hr
Battery	Battery Charging: WARNING: Explosive Gas! Batteries produce explosive hydrogen gas while being charged. To prevent a fire or explosion, charge batteries only in well ventilated areas. Keep sparks, open flames, and other sources of ignition away from the battery at all times. Keep batteries out of the reach of children. Remove all jewelry when servicing batteries.	—
Belt	Have Bendix starter drive serviced. Have solenoid shift starter disassembled and cleaned.	—	500 hr
Coolant	Check oil cooler fins, clean as necessary (if equipped).	—	250 hr
Oil	Change oil after every 100 hours of operation (more frequently under severe conditions). Refill with service class SG, SH, SJ or higher oil as specified in the “Viscosity Grades” table (Figure 3) on page 5.	—	100 hr
Spark plug	Check spark plug condition and gap.	—	250 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
Low-profile precleaner	Clean	25 hr	12 mo	Service/replace
Low-profile precleaner	Replace	25 hr	12 mo	Service/replace; or annually. Air Cleaner/Intake
Cooling shrouds	Clean	100 hr	12 mo	Remove cooling shrouds and clean cooling areas
Cooling shrouds and cooling areas	Clean	100 hr	12 mo	Remove cooling shrouds and clean cooling areas
Cooling shrouds/areas	Clean	100 hr	12 mo	Every 100 Hours or Annually; remove cooling shrouds and clean cooling areas
Engine oil	Change	100 hr	12 mo
Oil cooler fins	Check	100 hr	12 mo	Every 100 Hours or Annually (if equipped); clean as necessary
Oil cooler fins	Inspect	100 hr	12 mo	Check; clean as necessary (if equipped)
low-profile air cleaner element	Replace	100 hr	12 mo	Or annually
oil	Change	100 hr	12 mo	Or annually
Fuel filter	Replace	200 hr		Every 200 Hours
Oil filter	Change	200 hr		Every 200 Hours. Lubrication System
Heavy-duty air cleaner element	Replace	250 hr	12 mo	and check inner element
Heavy-duty air cleaner element / inner element	Replace	250 hr		Every 250 Hours; replace element and check inner element
heavy-duty air cleaner element and inner element	Replace	250 hr		Replace element and check inner element
Crankshaft spline	Lubricate	500 hr		Have a Kohler authorized dealer perform this service
Heavy-duty inner air cleaner element	Replace	500 hr	12 mo	Every 500 Hours
Spark plugs	Replace	500 hr	12 mo	and set gap. Electrical System

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
Angle	Maximum Angle of Operation	25	°	@ full oil level
Clearance	Camshaft End Play (w/shim)	0.076/0.127	mm	0.0030/0.0050 in.
Clearance	Camshaft Running Clearance	0.025/0.063	mm	0.0010/0.0025 in.
Clearance	Camshaft bore I.D. (max wear limit)	20.038 mm (0.7889 in.)	mm	max wear limit
Clearance	Camshaft bore I.D. (new)	20.000/20.025 mm (0.7874/0.7884 in.)	mm	new
Clearance	Camshaft end play (w/shim)	0.076/0.127 mm (0.0030/0.0050 in.)	mm
Clearance	Camshaft running clearance	0.025/0.063 mm (0.0010/0.0025 in.)	mm
Clearance	Connecting Rod-to-Crankpin Running Clearance	New: 0.030/0.055 mm (0.0012/0.0022 in.); Max Wear Limit: 0.070 mm (0.0028 in.)	mm (in.)
Clearance	Connecting Rod-to-Crankpin Running Clearance (Max. Wear Limit)	0.070	mm	0.0028 in.
Clearance	Connecting Rod-to-Crankpin Running Clearance (New)	0.030/0.055	mm	0.0012/0.0022 in.
Clearance	Connecting Rod-to-Crankpin Side Clearance	0.26/0.63	mm	0.0102/0.0248 in.
Clearance	Connecting rod-to-crankpin running clearance (max wear limit)	0.070 mm (0.0028 in.)	mm	max wear limit
Clearance	Connecting rod-to-crankpin running clearance (new)	0.030/0.055 mm (0.0012/0.0022 in.)	mm	new
Clearance	Connecting rod-to-crankpin running clearance, max wear limit	0.070	mm (0.0028 in.)	max wear limit
Clearance	Connecting rod-to-crankpin running clearance, new	0.030/0.055	mm (0.0012/0.0022 in.)	new
Clearance	Connecting rod-to-crankpin side clearance	0.26/0.63 mm (0.0102/0.0248 in.)	mm
Clearance	Crankshaft End Play (except CH25 below Serial No. 2403500008)	0.050/0.750	mm	0.0020/0.0295 in.
Clearance	Crankshaft End Play (free)	0.070/0.590	mm	0.0028/0.0230 in.
Clearance	Crankshaft End Play (w/thrust bearing components)	0.070/1.190	mm	0.0028/0.0468 in.
Clearance	Crankshaft end play (except CH25 engines below Serial No. 2403500008)	0.050/0.750 mm (0.0020/0.0295 in.)	mm
Clearance	Crankshaft end play (free)	0.070/0.590 mm (0.0028/0.0230 in.)	mm	free
Clearance	Crankshaft end play (thrust bearing models, for adjustment)	0.05/0.50 mm (0.0020/0.0197 in.)	mm
Clearance	Crankshaft end play (w/thrust bearing components)	0.070/0.270 mm (0.0028/0.0100 in.)	mm
Clearance	Cylinder Bore I.D.	New: 77.000/77.025 mm (3.0315/3.0325 in.); Max Wear Limit: 77.063 mm (3.0340 in.)	mm (in.)	77 mm bore
Clearance	Cylinder Bore I.D.	New: 80.000/80.025 mm (3.1496/3.1506 in.); Max Wear Limit: 80.065 mm (3.1522 in.)	mm (in.)	80 mm bore
Clearance	Cylinder Bore I.D.	New: 82.988/83.013 mm (3.2672/3.2682 in.); Max Wear Limit: 83.051 mm (3.2697 in.)	mm (in.)	83 mm bore
Clearance	Cylinder Head Max. Out-of-Flatness	0.076	mm	77 mm and 80 mm bores; 0.003 in.
Clearance	Cylinder Head Max. Out-of-Flatness	0.076 mm (0.003 in.) for 77 mm and 80 mm bores; 0.1 mm (0.004 in.) for 83 mm bore	mm (in.)
Clearance	Cylinder Head Max. Out-of-Flatness	0.1	mm	83 mm bore; 0.004 in.
Clearance	Cylinder bore I.D. (CH18/CH20/CH22/CH620-CH640, new)	77.000/77.025 mm (3.0315/3.0325 in.)	mm	new
Clearance	Cylinder bore I.D. (CH22/CH23/CH670-CH680, new)	80.000/80.025 mm (3.1496/3.1506 in.)	mm	new
Clearance	Cylinder bore I.D. (CH25/CH730/CH740/CH750, new)	82.988/83.013 mm (3.2672/3.2682 in.)	mm	new
Clearance	Cylinder head max out-of-flatness	0.076 mm (0.003 in.)	mm
Clearance	Exhaust Valve Guide I.D. Max. Wear Limit	7.159	mm	0.2819 in.
Clearance	Exhaust Valve Minimum Lift	8.07	mm	0.3177 in.
Clearance	Exhaust Valve Stem-to-Valve Guide Running Clearance	0.050/0.088	mm	0.0020/0.0035 in.
Clearance	Exhaust valve guide I.D. (max wear limit)	7.159 mm (0.2819 in.)	mm	max wear limit
Clearance	Exhaust valve minimum lift	8.07 mm (0.3177 in.)	mm
Clearance	Exhaust valve stem-to-guide running clearance	0.050/0.088	mm (0.0020/0.0035 in.)
Clearance	Exhaust valve stem-to-valve guide running clearance	0.050/0.088 mm (0.0020/0.0035 in.)	mm
Clearance	Governor cross shaft-to-crankcase running clearance, 6 mm shaft	0.013/0.075	mm (0.0005/0.0030 in.)	6 mm shaft
Clearance	Governor cross shaft-to-crankcase running clearance, 8 mm shaft	0.025/0.126	mm (0.0009/0.0049 in.)	8 mm shaft
Clearance	Hydraulic Valve Lifter to Crankcase Running Clearance	0.0241/0.0501	mm	0.0009/0.0020 in.
Clearance	Hydraulic valve lifter to crankcase running clearance	0.0241/0.0501 mm (0.0009/0.0020 in.)	mm
Clearance	Intake Valve Guide I.D. Max. Wear Limit	7.134	mm	0.2809 in.
Clearance	Intake Valve Minimum Lift	8.07	mm	0.3177 in.
Clearance	Intake Valve Stem-to-Valve Guide Running Clearance	0.038/0.076	mm	0.0015/0.0030 in.
Clearance	Intake valve guide I.D. (max wear limit)	7.134 mm (0.2809 in.)	mm	max wear limit
Clearance	Intake valve guide I.D. (new)	7.038/7.058 mm (0.2771/0.2779 in.)	mm	new
Clearance	Intake valve minimum lift	8.07 mm (0.3177 in.)	mm
Clearance	Intake valve stem-to-guide running clearance	0.038/0.076	mm (0.0015/0.0030 in.)
Clearance	Intake valve stem-to-valve guide running clearance	0.038/0.076 mm (0.0015/0.0030 in.)	mm
Clearance	Nominal Valve Seat Angle	45	°
Clearance	Nominal valve seat angle	45°	degrees
Clearance	Piston Thrust Face-to-Cylinder Bore Running Clearance (New, Style A)	0.039/0.082	mm	0.0015/0.0032 in.
Clearance	Piston pin O.D. (new)	16.995/17.000 mm (0.6691/0.6693 in.)	mm	new
Clearance	Piston-to-piston pin running clearance	0.006/0.017 mm (0.0002/0.0007 in.)	mm
Clearance	Spark plug gap	0.76 mm (0.030 in.)	mm
Clearance	Valve Guide Reamer Size (0.25 mm O.S.)	7.298	mm	0.2873 in.
Clearance	Valve Guide Reamer Size (Standard)	7.048	mm	0.2775 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	Capacity	Notes
Engine oil		API service class SJ or higher (including synthetic)		1.6 L	Kohler oils recommended. Select viscosity based on air temperature at time of operation (chart).
Engine oil	API service class SJ or higher (including synthetic)	API SJ or higher		1.6 L	Kohler oils recommended for best performance; select viscosity based on air temperature at time of operation (capacity is refill)
Engine oil	API service class SJ or higher; viscosity per temperature chart	API SJ or higher		1.6 L	Recommended Kohler oils; other high-quality detergent oils including synthetic acceptable.
Engine oil	Kohler oils; other high-quality detergent oils including synthetic	API service class SJ or higher		1.6 L	Select viscosity based on air temperature at time of operation: 5W-30, 10W-30, SAE 30
Engine oil	SAE 30 above 10°C (50°F); SAE 20 from -17.8°C (0°F) to 10°C (50°F); SAE 10 below -17.8°C (0°F)			0.47 L	Wet disc type clutch oil splash lubrication; use 0.47 L (1 pt.) of motor oil of proper viscosity.
Fuel	87 (R+M)/2 octane or higher; RON 90 octane minimum				Clean, fresh, unleaded gasoline. Up to 10% ethyl alcohol/90% unleaded acceptable; MTBE up to 15% by volume approved. Do not add oil. Do not use gasoline older than 30 days. E15, E20 and E85 are NOT approved.
Fuel	Clean, fresh, unleaded gasoline	Octane rating 87 (R+M)/2 or higher; RON 90 octane minimum			Gasoline up to 10% ethyl alcohol, 90% unleaded acceptable; MTBE and unleaded gasoline blend (max 15% MTBE by volume) approved; E15, E20 and E85 NOT approved; do not use gasoline older than 30 days
Fuel	Unleaded gasoline, 87 (R+M)/2 or higher; RON 90 octane minimum	Up to 10% ethyl alcohol; MTBE max 15% by volume			E15, E20 and E85 are NOT approved and should NOT be used; do not use gasoline older than 30 days.
Grease		Kohler 52 357 01-S (inertia drive) / 52 357 02-S (solenoid shift) starter drive lubricant; Kohler 25 357 12-S spline drive lubricant; Camshaft Lubricant Valspar ZZ613 (Kohler 25 357 14-S)			Lubricants/aids listed in Tools and Aids.
Other	SAE 30 above 10°C (50°F); SAE 20 -17.8°C (0°F) to 10°C (50°F); SAE 10 below -17.8°C (0°F)		-17°C to 10°C	0.47 L	Wet disc type clutch; oil splash type lubrication; use motor oil of proper viscosity
Other	SAE 30 above 10°C (50°F); SAE 20 from -17.8°C (0°F) to 10°C (50°F); SAE 10 below -17.8°C (0°F)		above -17°C	0.47 L	Wet disc type clutch oil (0.47 L / 1 pt.) motor oil of proper viscosity per chart
Other	SAE 30 above 10°C (50°F)	motor oil	above 10°C	0.47 L	Wet disc type clutch oil splash lubrication; use 0.47 L (1 pt.) of motor oil. SAE 20 for -17.8°C (0°F) to 10°C (50°F); SAE 10 for below -17.8°C (0°F).

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 Governed Idle Speed adjustment

Tools: Tachometer

Hold governor lever away from carburetor so throttle lever is against idle speed screw.
Start engine and warm up; adjust screw to approximately 1200 RPM.
Release governor lever and check throttle lever is in idle position.
Turn governed idle adjustment screw to obtain equipment manufacturer recommended idle speed (1500-1800 RPM).
Move throttle lever to wide-open/full throttle and set high speed screw to intended no-load RPM.

Adjust Low Idle Fuel adjustment

⚠ Do not attempt to remove limiter caps.

Place throttle control into idle or slow position; adjust low idle speed to 1200 RPM.
Turn low idle fuel adjusting needle out (counterclockwise) until engine speed decreases (rich); note position.
Turn needle in (clockwise); note position where speed decreases (lean).
Set adjusting needle midway between rich and lean settings.
Repeat for other low idle adjustment needle on two-barrel carburetor.
Recheck/adjust low idle speed to specified setting.

Adjust Low Idle Speed (RPM) adjustment

Tools: Tachometer

Place throttle control into idle or slow position.
Turn low idle speed adjusting screw in or out to obtain 1200 RPM (± 75 RPM).
Check speed using a tachometer.

Carburetor Low Idle Fuel Adjustment adjustment

⚠ Do not attempt to remove limiter caps.

Tools: tachometer

Place throttle control into idle or slow position; adjust low idle speed to 1200 RPM.
Turn low idle fuel adjusting needle out (counterclockwise) until engine speed decreases (rich); note position.
Turn needle in (clockwise) until engine speed decreases (lean); note position.
Set adjusting needle midway between rich and lean settings.
Repeat for other low idle adjustment needle on two-barrel carburetor.
Recheck/adjust low idle speed to specified setting.

Clutch Adjustment (wet disc type) adjustment

⚠ Do not attempt to pry or force spring lock away from ring.

Tools: large screwdriver

Release clutch and remove nameplate. Using a large screwdriver, turn adjusting ring clockwise, one notch at a time, until firm pressure is required to engage clutch.
After adjustment, engage clutch and check that rollers go over center to lock unit in engaged position and prevent releasing under load.
If trouble persists after readjustment, clutch reconditioning is indicated.

Determining Camshaft End Play adjustment

Tools: camshaft end play checking tool, feeler gauge

Install shim removed during disassembly onto camshaft.
Position camshaft end play checking tool on camshaft.
Apply pressure on checking tool (pushing camshaft toward crankshaft). Use a feeler gauge to measure camshaft end play between shim spacer and checking tool. End play should be 0.076/0.127 mm (0.003/0.
If end play is not within range, remove checking tool and replace shim as necessary.
Reinstall end play checking tool and recheck end play.

Digital Linear Actuator (DLA) Adjustment adjustment

Tools: Torque wrench

DLA must be in fully retracted position during assembly.
Loosen DLA mounting plate screws located on top of actuator plate.
With throttle linkage centered in U-Clip or secured with retaining clip at end of DLA shaft, slide DLA bracket assembly back until throttle plate is fully open.
Torque mounting plate screws to 2.5 N·m (22 in. lb.).

Governed Idle Speed Adjustment adjustment

Tools: tachometer, pliers

Hold governor lever away from carburetor so throttle lever is against idle speed adjustment screw. Start engine and warm up, then adjust screw to approximately 1200 RPM using a tachometer.
Release governor lever and check throttle lever is in idle position. Turn governed idle adjustment screw to obtain equipment manufacturer's recommended idle speed (1500-1800 RPM).
Move throttle lever to wide-open/full throttle and hold. Turn high speed screw to obtain intended high speed no-load RPM.

Governor Initial Adjustment adjustment

⚠ Do not tamper with governor setting. Overspeed is hazardous and could cause personal injury.

Tools: Torque wrench

Make sure throttle linkage is connected to governor arm and throttle lever on carburetor.
Loosen nut holding governor lever to cross shaft.
Move governor lever toward carburetor as far as it will go (wide open throttle) and hold in this position.
Insert a long thin rod or tool into hole on cross shaft and rotate shaft counterclockwise (viewed from end) as far as it will turn, then torque nut to 6.8 N·m (60 in. lb.).

Governor Sensitivity Adjustment adjustment

To increase sensitivity, move spring closer to governor cross shaft.
To decrease sensitivity, move spring away from governor cross shaft.

High Speed (RPM) Adjustment adjustment

Tools: Tachometer

With engine running, move throttle control to fast.
Turn inner adjustment screw outward to decrease, or inward to increase RPM speed.

Ignition Module Air Gap Adjustment adjustment

⚠ Do not attempt to set the gap with a business card or folded microfiche card. Use the feeler gauge specified.

Tools: Feeler gauge 0.30 mm (0.012 in.), Torque wrench

Turn flywheel magnet away from module position.
Attach module to mounting legs, pull it away from flywheel, and tighten screws temporarily.
Rotate flywheel so magnet is centered under module.
Position a 0.30 mm (0.012 in.) feeler gauge between magnet and all three legs of module.
Loosen mounting screws, allow magnet to pull module down against feeler gauge, and retighten mounting screws.
Rotate flywheel to remove feeler gauge, position magnet back under module, and recheck gap minimum 0.28 mm (0.011 in.) under each leg. Torque screws to 4.0 N·m (35 in. lb.).

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

Parts cataloged across the Kohler CH18 family

Part #	Description	Category
25 083 01-S	Outer Element, Heavy-Duty Air Cleaner	Air filter
25 083 04-S	Inner Element, Heavy-Duty Air Cleaner	Air filter
KO3226	Electric Starter Service Kit	Battery
25 755 20-S	Cleanout Kit (Black)	Cleanout kit
24 083 02-4	Oil Cooler, CH25	Oil cooler
24 083 05-4	Oil Cooler, CH26	Oil cooler
24 083 03-4	Paper Element, Heavy-Duty Air Cleaner	Paper element

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Aftermarket parts that fit this engine

4585301 FridayParts $32.35 4585309 FridayParts $24.00

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.

Common questions

Which generators use the Kohler CH18-25 engine?

The Kohler CH18-25 powers 1 generator set(s), including Kohler CH18.

How often should you change the oil in the Kohler CH18-25?

The Kohler CH18-25 oil change interval is every 100 hours.

What is a common problem with the Kohler CH18-25 engine?

A commonly reported issue on generators using the Kohler CH18-25 is: Will Not Start. Cause: Improper Fuel, Dirty Fuel Line/System, Grass Screen, Overloaded. Fix: Clean or replace fuel filter; clean air cleaner element and precleaner; ensure proper battery condition..