The Kohler CH640 is a 624 cc, (38.0 cu·in) for early version or 674 cc, (41.0 cu·in) for later version V-twin air-cooled four-stroke internal combustion gasoline engine from the Command PRO series, manufactured by Kohler Co.
The Kohler CH640 engine has an OHV (overhead valve) design, an aluminum block with cast iron cylinder liners, a horizontal PTO-shaft, pressurized lubrication system. This engine is equipped with a carburetor (Nikki or Keihin) with a fixed main jet and one of these ignition systems: CDI/MDI, ASAM/DSAM, DSAI (Digital Spark Advance Ignition).
The cylinder bore and the piston stroke are 77.0 mm (3.03 in) and 67.0 mm (2.64 in), respectively for the CH640 engine with 624 cc of displacement, and 80.0 mm (3.15 in) and 67.0 mm (2.64 in), respectively for 674 cc engine. Compression ratio rating is 8.5:1.
The Kohler CH640 engine produced 20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm of horsepower and 48.4 Nm (4.94 kg·m; 35.72 ft·lb) at 2,400 rpm of torque.
The breakdown of the engine code is as follows:
- C – Command series
- H – Horizontal PTO shaft
- 640 – Numerical designation
General information
| Engine Specifications | |
| Model | Command PRO CH640 |
| Type | 4-stroke, OHV, V-twin |
| Displacement |
624 cm 3 (38.0 cu-in) 674 cm 3 (41.0 cu-in) |
| Max. horsepower | 20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm |
| Max. torque | 48.4 Nm (4.94 kg·m; 35.72 ft·lb) at 2,400 rpm |
| Fuel system | Carburetor with a fixed main jet (Nikki or Keihin) |
| Cooling system | Forced-air |
| Ignition system | CDI/MDI, ASAM/DSAM, DSAI (Digital Spark Advance Ignition) |
| Lubricating system | Pressurized lubrication |
| Starting system | Electric starter |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Dimensions (L x W X H) | 355 x 451 x 483 mm (14.0 x 17.7 x 19.0 in) |
| Dry weight | 41.0 kg (90.0 lbs) |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: | 8.5:1 | |
| Bore x Stroke |
624 cc: 77.0 mm X 67.0 mm (3.03 x 2.64 in) 674 cc: 80.0 mm X 67.0 mm (3.15 x 2.64 in) |
|
| Sleeve internal diameter |
624 cc: 77.000-77.025 mm (3.0315-3.0325 in) 674 cc: 80.000-80.025 mm (3.1496-3.1506 in) |
|
| Number of piston rings (compression / oil): | 2 / 1 | |
| 624 cc | ||
| Thrust face outer diameter | 76.943-76.961 mm (3.0292-3.0299 in) | |
| Piston pin outer diameter | 16.995-17.000 mm (0.6691-0.6693 in) | |
| Ring-to-groove side clearance: | Top | 0.040-0.080 mm (0.0016-0.0031 in) |
| Second | 0.040-0.080 mm (0.0016-0.0031 in) | |
| 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) |
| Second | 0.250-0.450 mm (0.0098-0.0177 in) | |
| 674 cc | ||
| Piston style A | ||
| Thrust face outer diameter | 79.943-79.961 mm (3.1473-3.1480 in) | |
| Piston pin outer diameter | 16.995-17.000 mm (0.6691-0.6693 in) | |
| Ring-to-groove side clearance: | Top | 0.030-0.076 mm (0.0012-0.0030 in) |
| Second | 0.030-0.076 mm (0.0012-0.0030 in) | |
| Oil | 0.046-0.196 mm (0.0018-0.0077 in) | |
| Ring end gap: | Top | 0.180-0.460 mm (0.0071-0.0181 in) |
| Second | 0.180-0.460 mm (0.0071-0.0181 in) | |
| Piston style B | ||
| Thrust face outer diameter | 79.966 mm (3.1483 in) | |
| Piston pin outer diameter | 16.995-17.000 mm (0.6691-0.6693 in) | |
| Ring-to-groove side clearance: | Top | 0.030-0.070 mm (0.001-0.0026 in) |
| Second | 0.030-0.070 mm (0.001-0.0026 in) | |
| Oil | 0.060-0.190 mm (0.0022-0.0073 in) | |
| Ring end gap: | Top | 0.100-0.279 mm (0.0039-0.0110 in) |
| Second | 1.400-1.679 mm (0.0551-0.0661 in) | |
| 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) | |
| Cylinder Head | ||
| Valve Arrangement: | OHV, gear drive | |
| Valves: | 4 (2 per cylinder) | |
| Valve head diameter: | INTAKE | 33.370-33.630 mm (1.3138-1.324 in) |
| EXHAUST | 29.370-29.630 mm (1.1563-1.1665 in) | |
| Stem outer diameter: | INTAKE | 6.982-7.000 mm (0.2749-0.2756 in) |
| EXHAUST | 6.970-6.988 mm (0.2744-0.2751 in) | |
Tightening torque specs
| Tightening torque specs | |
| 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) |
| Flywheel | 66.4 Nm (6.77 kg·m; 49 ft·lb) |
| Spark plug | 27 Nm (2.75 kg·m; 20.0 ft·lb) |
Service Information
| Oil system | |
| 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) |
| Ignition system | |
| Spark plug | Champion RC12YC |
| Spark plug gap | 0.76 mm (0.030 in) |
| Ignition module air gap | 0.280-0.330 mm (0.011-0.013 in) |
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