Kohler K91

Kohler K91The Kohler K91 is a 145 cc (8.86 cu·in) single-cylinder air-cooled four-stroke internal combustion gasoline engine from K-series, manufactured by Kohler Co.

The Kohler K91 engine has an L-head (side valve) design and horizontal PTO-shaft. This engine can be equipped with Kohler or Walbro carburetor and magneto, battery or breakerless ignition systems. The K91 engine used paper air cleaner (oiled foam precleaner was available as an option).

The cylinder bore is 60.33 mm (2.38 in) and the piston stroke is 50.80 mm (2 in). This engine produced 4.1 PS (3.0 kW; 4.0 HP) at 4,000 rpm of horsepower.

The breakdown of the engine code is as follows:

  • K – K-series
  • 9 – Approximate daisplacement (cu·in)
  • 1 – Single cylinder
  • Suffix (engine is available with the following options):
    S – Electric starter;
    T – Retractable starter;
    ST – Electric and retractable starter;
    EP – Electric plant;
    A – Special oil pan;
    C – Clutch model;
    G – Generator applications;
    P – Pump model;
    Q – Quled model;
    R – Reduction gear;

General information

Engine Specifications
Model K91
Type 4-stroke, L-head, single cylinder
Displacement 145 cm 3 (8.86 cu-in)
Max. horsepower 4.1 PS (3.0 kW; 4.0 HP) at 4,000 rpm
Max. torque (crank PTO)
Fuel system Carburetor (Kohler or Walbro, fixed main jet or adjustable main jet)
Cooling system Forced-air
Ignition system Magneto or battery or breakerless ignition system
Lubricating system Splash type
Starting system Recoil or electric starter
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity

Cylinder Block and Head

Cylinder block
Compression ratio:
Bore x Stroke 60.33 X 50.80 mm (2.375 x 2.000 in)
Sleeve internal diameter 60.312-60.337 mm (2.3745-2.3755 in)
Piston skirt outer diameter 60.172-60.223 mm (2.369-2.371 in)
Number of piston rings (compression / oil): 2 / 1
Ring end gap Top 0.177-0.432 mm (0.007-0.017 in)
Second 0.177-0.432 mm (0.007-0.017 in)
Connecting rod small end ID 14.300 mm (0.563 in)
Piston pin outer diameter 14.282-14.287 mm (0.5623-0.5625 in)
Cylinder Head
Valve Arrangement: L-head (sidevalve)
Valves: 2
Valve head diameter: INTAKE 24.866-25.120 mm (0.979-0.989 in)
EXHAUST 20.498-20.752 mm (0.807-0.817 in)
Stem outer diameter (standard): INTAKE 6.299-6.312 mm (0.248-0.2485 in)
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 Information

Max 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
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.)
Ignition system
Spark plug Champion: RJ8C
Spark plug gap 0.65 mm (0.0256 in)
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We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.

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