Kohler CH12.5/CH12.5S (12.5 HP) engine specs and service data

The Kohler CH12.5/CH12.5S is a 398 cc (24.3 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine from the Command PRO series with a horizontal shaft, manufactured by Kohler Co for general-purpose applications.

The cylinder bore and the piston stroke are 87.0 mm (3.43 in) and 67.0 mm (2.64 in), respectively. Compression ratio rating is 8.5:1.

The Kohler CH12.5 engine produced 12.7 PS (9.33 KW; 12.5 HP) at 3,600 rpm of horsepower and 27.8 Nm (2.8 kg·m; 20.5 ft·lb) at 2,500 rpm of torque..

The Kohler CH12.5 features:

OHV design
Hydraulic valve lifters
Aluminum cylinder block
Cast iron cylinder liners
Dependable electronic magneto ignition system
Carburetor with fixed main jet (Nikki or Keihin)
Mechanical centrifugal governor
Full pressure lubrication system
Forced air cooling system
Electric starter

General information

Engine Specifications
Engine model	Command PRO CH12.5/CH12.5S
Engine type	4-stroke, OHV, single-cylinder
Displacement	398 cm ³ (24.3 cu-in)
Max. horsepower	12.7 PS (9.33 KW; 12.5 HP) at 3,600 rpm
Max. torque	27.8 Nm (2.8 kg·m; 20.5 ft·lb) at 2,500 rpm
Cooling system	Forced air
Air cleaner	Replaceable, paper element
Lubricating system	Full pressure
Ignition system	Dependable electronic magneto
Fuel system	Carburetor with fixed main jet (Nikki or Keihin)
Fuel used	Unleaded gasoline (octane number 86 or higher)
Starting system	Electric starter
Governor	Mechanical centrifugal governor
PTO shaft rotation	Counterclockwise (from PTO shaft side)
Dimensions (L x W X H)	340 x 502 x 449 mm (13.41 x 19.8 x 17.7 in)
Dry weight	39.5 kg (87.1 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio:	8.5:1
Cylinder bore:	87.0 mm (3.43 in)
Piston stroke:	67.0 mm (2.64 in)
Cylinder internal diameter (standard):	87.000-87.025 mm (3.4252-3.4262 in)
Number of piston rings (compression / oil):	2/1
Piston pin diameter:	18.995-19.000 mm (0.7478-0.748 in)
Thrust face outer diameter (standard):	86.941-86.959 mm (3.4229-3.4236 in)
Ring-to-groove side clearance (Top):	0.040-0.105 mm (0.0016-0.0041 in)
Ring-to-groove side clearance (Second):	0.040-0.072 mm (0.0016-0.0028 in)
Ring-to-groove side clearance (Oil):	0.551-0.675 mm (0.0217-0.0266 in)
Ring end gap (Top):	0.300-0.500 mm (0.0120-0.0197 in)
Ring end gap (Second):	0.300-0.500 mm (0.0120-0.0197 in)
Number of main bearings:	2
Crankshaft main bearing journal diameter:	Flywheel end: 44.913-44.935 mm (1.7682-1.7691 in) Oil pan end: 41.915-41.935 mm (1.6502-1.6510 in)
Crankpin journal diameter:	38.958-30.970 mm (1.5338-1.2193 in)
Balance shaft bearing surface OD:	19.962-19.975 mm (0.7859-0.7864 in)
Cylinder head
Valve arrangement:	OHV, gear driven
Valves:	2
Valve head diameter (INTAKE):	35.370-35.630 mm (1.3925-1.4028 in)
Valve head diameter (EXHAUST):	31.370-31.630 mm (1.235-1.2453 in)
Valve seat angle (INTAKE):	89°
Valve seat angle (EXHAUST):	89°
Valve seat angle (INTAKE):	45°
Valve seat angle (EXHAUST):	45°
Valve steam diameter (INTAKE):	6.982-7.000 mm (0.2749-0.2756 in)
Valve steam diameter (EXHAUST):	6.970-6.988 mm (0.2744-0.2751 in)
Valve lift minimal (INTAKE):	8.96 mm (0.353 in)
Valve lift minimal (EXHAUST):	9.14 mm (0.360 in)
Camshaft journal diameter :	19.962-19.975 mm (0.7859-0.7864 in)

Tightening torque specs

Tightening torque specs
Connecting rod	8 mm straight shank: 22.7 Nm (2.32 kg·m; 16.75 ft·lb) 8 mm step-down: 14.7 Nm (1.5 kg·m; 10.85 ft·lb) 6 mm straight shank: 11.3 Nm (1.15 kg·m; 8.34 ft·lb)
Cylinder head (torque in 2 increments)	Step 1: 20.0 Nm (2.0 kg·m; 15.0 ft·lb) Step 2: 40.0 Nm (4.0 kg·m; 30.0 ft·lb)
Fan	9.9 Nm (1.0 kg·m; 7.3 ft·lb)
Flywheel	66.4 Nm (6.77 kg·m; 49.0 ft·lb)
Muﬄer retaining nuts	24.4 Nm (2.5 kg·m; 18.0 ft·lb)
Spark plug	38.0-43.4 Nm (3.9-4.4 kgf·m; 28.0-32.0 lb·ft)
Oil drain plug	7.3-9.0 Nm (0.7-0.9 kgf·m; 5.4-6.6 lb·ft)

Service Data

Engine
Maximum speed:	3600±50 rpm
Idle speed:	1200±75 rpm
Compression pressure
Standard:	1.1 MPa (160 psi)
Compression differential limit between cylinders:	15% and less
Oil system
Lubrication system:	Full pressure
Oil type:	API SG, SH, SJ, or higher
Recommended oil:	SAE 10W-30
Oil capacity:	W/o oil filter: 1.7 L (1.8 US. qt, 1.5 Imp. qt.) With oil filter: 1.9 L (2.0 US.qts, 1.7 Imp. qts)
Fuel system
Type:	Carburetor with fixed main jet (Nikki or Keihin)
Fuel pump:	Pulse type
Fuel filter:	In-line
Ignition system
Type:	Dependable electronic magneto
Spark plug:	Champion RC12YC or Platinum 3071
Spark plug gap	1.02 mm (0.040 in)
Ignition coil air gap	0.200-0.300 mm (0.0079-0.0118 in)

Applications

Manufacturer or Brand	Models
Lawn tractors
Cub Cadet	AGS 2130, HDS 2135

References

1. Kohler Command CH11-16 horizontal crankshaft service manual. Kohler Co. 1990.

Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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Kohler CH12.5