Kohler CH640

Kohler CH640The Kohler CH640 is a 624 cc, (38.0 cu·in) or 674 cc, (41.0 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 for the 624 cc version or an 80.0 mm (3.15 in) cylinder bore and 67.0 mm (2.64 in) piston stroke for the 674 cc version. The compression ratio rating is 8.5:1.

The CH640 engine produced 20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm maximum horsepower and 48.4 Nm (4.94 kg·m; 35.72 ft·lb) at 2,400 rpm of maximum torque.

The Kohler CH640 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 modelCommand PRO CH640
Engine type4-stroke, OHV, V-twin
Displacement 624 cm 3 (38.0 cu-in)
674 cm 3 (41.0 cu-in)
Max. horsepower20.8 PS (15.3 KW; 20.5 HP) at 3,600 rpm
Max. torque48.4 Nm (4.94 kg·m; 35.72 ft·lb) at 2,400 rpm
Cooling systemForced air
Air cleanerReplaceable, paper element
Lubricating systemFull pressure
Ignition systemElectronic ignition
Fuel systemCarburetor with fixed main jet (Nikki or Keihin)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemElectric starter
GovernorMechanical centrifugal governor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)355 x 451 x 483 mm (14.0 x 17.7 x 19.0 in)
Dry weight41.0 kg (90.0 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio:8.5:1
Cylinder bore: 624 cc: 77.0 mm (3.03 in)
674 cc: 80.0 mm (3.15 in)
Piston stroke:67.0 mm (2.64 in)
Cylinder internal diameter (standard): 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
Piston pin diameter:16.995-17.000 mm (0.6691-0.6693 in)
624 cc
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)
674 cc
Piston style A
Thrust face outer diameter (standard):79.943-79.961 mm (3.1473-3.1480 in)
Side clearance (Top):0.030-0.076 mm (0.0012-0.0030 in)
Side clearance (Second):0.030-0.076 mm (0.0012-0.0030 in)
Side clearance (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)
Ring end gap (Second):0.180-0.460 mm (0.0071-0.0181 in)
Piston style B
Thrust face outer diameter (standard):79.966 mm (3.1483 in)
Side clearance (Top):0.030-0.070 mm (0.0010-0.0026 in)
Side clearance (Second):0.030-0.070 mm (0.0010-0.0026 in)
Side clearance (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)
Ring end gap (Second):1.400-1.679 mm (0.0551-0.0661 in)
Crankshaft
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 nut6.2-7.3 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)
Fan9.9 Nm (1.0 kg·m; 7.3 ft·lb)
Flywheel66.4 Nm (6.77 kg·m; 49.0 ft·lb)
Governor lever nut6.8 Nm (0.69 kg·m; 5.02 ft·lb)
Muffler retaining nuts24.4 Nm (2.5 kg·m; 18.0 ft·lb)
Spark plug27 Nm (2.75 kg·m; 20.0 ft·lb)
Oil drain plug13.6 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 gap0.280-0.330 mm (0.011-0.013 in)

References

1. Kohler Command CH18-CH25, CH620-CH730, CH740, CH750 service manual. Kohler Co. 2022.

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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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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