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
Type4-stroke, L-head, single cylinder
Displacement145 cm 3 (8.86 cu-in)
Max. horsepower4.1 PS (3.0 kW; 4.0 HP) at 4,000 rpm
Max. torque (crank PTO)
Fuel systemCarburetor (Kohler or Walbro, fixed main jet or adjustable main jet)
Cooling systemForced-air
Ignition systemMagneto or battery or breakerless ignition system
Lubricating systemSplash type
Starting systemRecoil or electric starter
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity

Cylinder Block and Head

Cylinder block
Compression ratio:
Bore x Stroke60.33 X 50.80 mm (2.375 x 2.000 in)
Sleeve internal diameter60.312-60.337 mm (2.3745-2.3755 in)
Piston skirt outer diameter60.172-60.223 mm (2.369-2.371 in)
Number of piston rings (compression / oil):2 / 1
Ring end gapTop0.177-0.432 mm (0.007-0.017 in)
Second0.177-0.432 mm (0.007-0.017 in)
Connecting rod small end ID14.300 mm (0.563 in)
Piston pin outer diameter14.282-14.287 mm (0.5623-0.5625 in)
Cylinder Head
Valve Arrangement:L-head (sidevalve)
Valve head diameter:INTAKE24.866-25.120 mm (0.979-0.989 in)
EXHAUST20.498-20.752 mm (0.807-0.817 in)
Stem outer diameter (standard):INTAKE6.299-6.312 mm (0.248-0.2485 in)
EXHAUST6.248-6.261 mm (0.246-0.2465 in)

Tightening torque specs

Tightening torque specs
Cylinder head bolt23 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 plug25-30 Nm; 2.55-3.06 kg·m; 18-22 ft·lb

Service Information

Max speed4,000 rpm
Valve clearance
Intake valve clearance0.13-0.23 mm (0.0051-0.0091 in)
Exhaust valve clearance0.28-0.38 mm (0.011-0.015 in)
Oil system
Oil typeAPI SF or SG
Recommended oil Summer: SAE 30W
Winter: SAE 5W-20, 5W-30
Oil capacity0.7 L (0.74 US. qt, 0.62 Imp. qt.)
Ignition system
Spark plugChampion: RJ8C
Spark plug gap0.65 mm (0.0256 in)
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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