The Kohler CH641 is a 624 cc (38.0 cu·in) natural aspirated V-twin 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.
It has a 77.0 mm (3.03 in) cylinder bore and 67.0 mm (2.64 in) piston stroke. The compression ratio rating is 8.5:1.
The CH641 engine produced 20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm maximum horsepower, and 44.3 Nm (4.52 kg·m; 32.69 ft·lb) at 2,400 rpm of maximum torque.
The Kohler CH641 features:
- OHV design
- Hydraulic valve lifters
- Aluminum cylinder block
- Cast iron cylinder liners
- Hardened crank journals
- PTO side-load sleeve bearing
- Electronic 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 CH641 |
| Engine type | 4-stroke, OHV, V-twin |
| Displacement | 624 cm 3 (38.0 cu-in) |
| Max. horsepower | 20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm |
| Max. torque | 44.3 Nm (4.5 kg·m; 32.7 ft·lb) at 2,400 rpm |
| Cooling system | Forced air |
| Air cleaner | Replaceable, paper element |
| Lubricating system | Full pressure |
| Ignition system | Electronic ignition |
| 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) | 538 x 451 x 363 mm (21.2 x 17.7 x 14.3 in) |
| Dry weight | 41.0 kg (90.0 lbs) |
Cylinder Block and Head
| Cylinder block | |
| Compression ratio: | 8.5:1 |
| Cylinder bore: | 77.0 mm (3.03 in) |
| Piston stroke: | 67.0 mm (2.64 in) |
| Cylinder internal diameter (standard): | 77.000-77.025 mm (3.0315-3.0325 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Piston pin diameter: | 16.995-17.000 mm (0.6691-0.6693 in) |
| Thrust face outer diameter (standard): | 76.943-76.961 mm (3.0292-3.0299 in) |
| Side clearance (Top): | 0.040-0.080 mm (0.0016-0.0031 in) |
| Side clearance (Second): | 0.040-0.080 mm (0.0016-0.0031 in) |
| Side clearance (Oil): | 0.060-0.202 mm (0.0024-0.0080 in) |
| Ring end gap (Top): | 0.250-0.450 mm (0.0098-0.0177 in) |
| Ring end gap (Second): | 0.250-0.450 mm (0.0098-0.0177 in) |
| Number of main bearings: | 2 |
| Crankshaft main journal diameter: | 40.913-40.935 mm (1.6107-1.6116 in) |
| Crankpin journal diameter: | 35.955-35.973 mm (1.4155-1.4163 in) |
| Crankshaft center distance: | 33.5 mm (1.32 in) |
| Cylinder head | |
| Valve arrangement: | OHV, gear driven |
| Valves: | 2 (4 valves in total) |
| Valve head diameter (INTAKE): | 33.370-33.630 mm (1.3138-1.324 in) |
| Valve head diameter (EXHAUST): | 29.370-29.630 mm (1.1563-1.1665 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): | 8.07 mm (0.3177 in) |
| Valve lift minimal (EXHAUST): | 8.07 mm (0.3177 in) |
| Camshaft journal diameter : | 19.962-19.975 mm (0.7859-0.7864 in) |
Tightening torque specs
| Tightening torque specs | |
| Intake manifold mounting (torque in 2 increments) | Step 1: 7.4 Nm (0.75 kg·m; 5.5 ft·lb) Step 2: 9.9 Nm (1.00 kg·m; 7.3 ft·lb) |
| 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) |
| Carburetor mounting nut | 6.2-7.3 Nm (0.63-0.74 kg·m; 4.6-5.4 ft·lb) |
| Cylinder head | Nut (torque in 2 increments): Step 1: 16.9 Nm (1.72 kg·m; 12.5 ft·lb) Step 2: 35.5 Nm (3.62 kg·m; 26.2 ft·lb) Bolt (torque in 2 increments) Step 1: 22.6 Nm (2.31 kg·m; 16.7 ft·lb) Step 2: 41.8 Nm (4.26 kg·m; 30.8 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) |
| Governor lever nut | 6.8 Nm (0.69 kg·m; 5.02 ft·lb) |
| Muffler retaining nuts | 24.4 Nm (2.5 kg·m; 18.0 ft·lb) |
| Spark plug | 27 Nm (2.75 kg·m; 20.0 ft·lb) |
| Oil drain plug | 13.6 Nm (1.4 kg·m; 10.0 ft·lb) |
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: | Electronic ignition system |
| Spark plug: | Champion RC12YC |
| Spark plug gap: | 0.76 mm (0.030 in) |
| Ignition coil air gap | 0.280-0.330 mm (0.011-0.013 in) |
References
1. Kohler Command CH18-CH25, CH620-CH730, CH740, CH750 service manual. Kohler Co. 2022.
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