Kohler K91

Kohler K91The Kohler K91 is a 145 cc, (8.85 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Kohler Co for general-purpose applications.

It has a 60.33 mm (2.38 in) cylinder bore and 50.80 mm (2 in) piston stroke. The K91 engine produced 4.1 PS (3 kW; 4.0 HP) at 4,000 rpm of maximum horsepower.

The Kohler K91 features:

  • L-head (side valve) design
  • Magneto ignition system, battery ignition system or breakerless ignition system ignition system*
  • Carburetor (Kohler or Walbro – fixed main jet or adjustable main jet)*
  • Centrifugal governor
  • Splash type lubrication system
  • Forced air cooling system
  • Recoil or electric starter

*-depending on modification

General information

Engine Specifications
Engine model K91
Engine type 4-stroke, L-head, single-cylinder
Displacement 145 cm3, (8.85 cu·in)
Max. horsepower 4.1 PS (3.0 kW; 4.0 HP) at 4,000 rpm
Max. torque
Cooling system Forced air
Air cleaner Paper air cleaner (oiled foam precleaner)
Lubricating system Splash type
Ignition system Magneto ignition system, battery ignition system, breakerless ignition system
Fuel system Carburetor (Kohler or Walbro – fixed main jet or adjustable main jet)
Fuel consumption
Fuel tank capacity
Fuel used Unleaded gasoline (octane number 86 or higher)
Starting system Recoil or electric starter
Governor Centrifugal governor
PTO shaft rotation Counterclockwise (from PTO shaft side)
Dimensions (L x W X H)
Dry weight 19.5 kg (43 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio:
Cylinder bore: 60.33 mm (2.38 in)
Piston stroke: 50.80 mm (2 in)
Cylinder internal diameter (standard): 60.312-60.337 mm (2.3745-2.3755 in)
Piston skirt outer diameter (standard): 60.172-60.223 mm (2.369-2.371 in)
Number of piston rings (compression / oil): 2/1
Connecting rod small end diameter (standard): 14.300 mm (0.563 in)
Piston pin diameter: 14.282-14.287 mm (0.5623-0.5625 in)
Ring end gap (Top): 0.177-0.432 mm (0.007-0.017 in)
Ring end gap (Second): 0.177-0.432 mm (0.007-0.017 in)
Crankshaft center distance: 25.4 mm (1 in)
Cylinder head
Valve arrangement: L-head (side valve)
Valves: 2
Valve head diameter (INTAKE): 24.866-25.120 mm (0.979-0.989 in)
Valve head diameter (EXHAUST): 20.498-20.752 mm (0.807-0.817 in)
Valve steam diameter (INTAKE): 6.299-6.312 mm (0.248-0.2485 in)
Valve steam diameter (EXHAUST): 6.248-6.261 mm (0.246-0.2465 in)

Tightening torque specs

Tightening torque specs
Cylinder head bolt 23 Nm; 2.3 kg·m; 17 ft·lb
Flywheel Nut: 55-68 Nm; 5.5-6.9 kg·m; 40-50 ft·lb
Screw: 28 Nm; 2.9 kg·m; 21 ft·lb
Spark plug 25-30 Nm; 2.55-3.06 kg·m; 18-22 ft·lb

Service Data

Engine
Maximum speed: 4,000 rpm
Valve clearance
Intake valve clearance: 0.13-0.23 mm (0.0051-0.0091 in)
Exhaust valve clearance: 0.28-0.38 mm (0.011-0.015 in)
Oil system
Lubrication system: Splash type
Oil type: API: SF or SG
Recommended oil: Summer: SAE 30W
Winter: SAE 5W-20, 5W-30
Oil capacity: 0.7 L (0.74 US. qt, 0.62 Imp. qt.)
Fuel system
Type: Carburetor (Kohler or Walbro – fixed main jet or adjustable main jet)
Ignition system
Type: Magneto ignition system, battery ignition system, breakerless ignition system
Spark plug: Champion RJ8C
Spark plug gap: 0.65 mm (0.0256 in)

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