The Kohler RH255 is a 196 cc (12.0 cu·in) single-cylinder air-cooled four-stroke internal combustion gasoline engine from SH/3000/Courage series, manufactured by Kohler Co., for general-purpose applications.
The Kohler RH255 engine has an OHV (overhead valve) design, aluminum block with cast iron cylinder liners. This engine is equipped with one-barrel carburetor with fixed main jet, dependable magneto breakerless ignition system and mechanical governor.
Cylinder bore and piston stroke are 68.0 mm (2.7 in) and 54.0 mm (2.1 in), respectively. Compression ratio rating is 8.5:1.
The RH255 engine produced 5.7 PS (4.2 KW; 5.5 HP) at 3,600 rpm of horsepower and 14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm of torque.
The breakdown of the engine code is as follows:
- RH – RH series
- 2 – Slanted cylinder
- 55 – Output power 5.5 HP
General information
| Engine Specifications | |
| Model | Kohler RH255 |
| Type | 4-stroke, OHV, single cylinder |
| Displacement | 196 cm 3 (12.0 cu-in) |
| Max. horsepower | 5.7 PS (4.2 KW; 5.5 HP) at 3,600 rpm |
| Max. torque (crank PTO) | 14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm |
| Fuel system | One-barrel carburetor with fixed main jet |
| Cooling system | Forced-air |
| Ignition system | Dependable magneto breakerless |
| Lubricating system | Splash type |
| Starting system | Recoil/12V electric (optional) starter |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 2.0 liters (2.10 US.qts, 1.75 Imp. qts) |
| Dimensions (L x W x H) | 310x329x325 mm (12.2×12.8×12.8 in) |
| Weight | 16.0 kg (35.3 lbs) |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: | 8.5:1 | |
| Bore x Stroke | 68.0 X 54.0 mm (2.7 x 2.1 in) | |
| Sleeve internal diameter | 68.015-68.030 mm (2.6770-2.6780 in) | |
| Piston skirt outer diameter | 67.965-67.985 mm (2.6758-2.6766 in) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Ring side clearance | Top | 0.030-0.070 mm (0.0012-0.0028 in) |
| Second | 0.020-0.060 mm (0.0008-0.0024 in) | |
| Oil | 0.040-0.200 mm (0.0016-0.0079 in) | |
| Ring end gap | Top | 0.147-0.344 mm (0.0058-0.0136 in) |
| Second | 0.347-0.594 mm (0.0137-0.0234 in) | |
| Connecting rod small end ID | 18.010-18.015 mm (0.7090-0.7092 in) | |
| Connecting rod big end ID | 30.021-30.026 mm (1.1819-1.1821 in) | |
| Piston pin outer diameter | 17.992-17.995 mm (0.7083-0.7084 in) | |
| Main bearing journal outer diameter: | 24.975-24.989 mm (0.9833-0.9838 in) | |
| Connecting rod journal outer diameter: | 29.975-29.985 mm (1.1801-1.1805 in) | |
| Cylinder Head | ||
| Valve Arrangement: | OHV | |
| Valves: | 2 | |
| Valve head diameter: | INTAKE | 25.000 mm (0.9842 in) |
| EXHAUST | 24.000 mm (0.9449 in) | |
| Stem outer diameter (standard): | INTAKE | 5.500 mm (0.2165 in) |
| EXHAUST | 5.500 mm (0.2165 in) | |
| Valve length (standard): | INTAKE | 64.000 mm (2.5197 in) |
| EXHAUST | 62.000 mm (2.4409 in) | |
Tightening torque specs
| Tightening torque specs | |
| Cylinder head (torque in 2 increments) |
Step 1: 12.0 Nm (1.2 kgf·m; 8.9 ft·lb) Step 2: 24.0 Nm (2.4 kgf·m; 17.7 ft·lb) |
| Connecting rod | 12.0 Nm (1.2 kgf·m; 8.9 ft·lb) |
| Flywheel | 74.0 Nm (7.5 kgf·m; 54.6 ft·lb) |
| Oil drain plug | 18.0 Nm; (1.8 kg·m; 13.3 ft·lb) |
| Spark plug | 27.0 Nm (2.8 kgf·m; 19.9 ft·lb) |
Service Information
| Engine | |
| Idle speed | 2,000 ± 150 rpm |
| Valve clearance | |
| Intake valve clearance | 0.100 mm (0.0040 in) |
| Exhaust valve clearance | 0.150 mm (0.0060 in) |
| Oil system | |
| Oil type | API SJ or higher |
| Recommended oil | SAE 10W-30 |
| Oil capacity | 0.6 L (0.63 US. qt, 0.53 Imp. qt.) |
| Ignition system | |
| Spark plug | Champion: RC12YC |
| Spark plug gap | 0.76 mm (0.030 in) |
| Ignition module air gap | 0.254 mm (0.0100 in) |
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