The Kohler RH255 is a 196 cc (12.0 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine from the 2000/RH series with a horizontal shaft, manufactured by Kohler Co for general-purpose applications.
The cylinder bore and the piston stroke are 68.0 mm (2.70 in) and 54.0 mm (2.1 in), respectively. Compression ratio rating is 8.5:1.
The Kohler RH255 engine produced 5.7 PS (4.2 KW; 5.5 HP) at 3,600 rpm of maximum horsepower and 14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm of peak torque.
The Kohler RH255 features:
- OHV design
- Aluminum cylinder block
- Cast iron cylinder liners
- Dependable magneto breakerless ignition system
- One-barrel carburetor with fixed main jet
- Automatic compression release
- Mechanical centrifugal governor
- High-inertia flywheel
- Splash type lubrication system
- Forced air cooling system
- Recoil or electric (optional) starter
General information
| Engine Specifications | |
| Engine model | RH255 |
| Engine 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 | 14.2 Nm (1.45 kg·m; 10.5 ft·lb) at 3,000 rpm |
| Cooling system | Forced air |
| Air cleaner | Replaceable, dual type |
| Lubricating system | Splash type |
| Ignition system | Dependable magneto breakerless ignition system |
| Fuel system | One-barrel carburetor with fixed main jet |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 2.0 liters (2.10 US.qts, 1.75 Imp. qts) |
| Starting system | Recoil or electric starter |
| Governor | Mechanical centrifugal governor |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Dimensions (L x W X H) | 310x329x325 mm (12.2×12.8×12.8 in) |
| Dry weight | 16.0 kg (35.3 lbs) |
Cylinder Block and Head
| Cylinder block | |
| Compression ratio: | 8.5:1 |
| Cylinder bore: | 68.0 mm (2.7 in) |
| Piston stroke: | 54.0 mm (2.1 in) |
| Cylinder internal diameter (standard): | 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 |
| Piston pin diameter: | 17.992-17.995 mm (0.7083-0.7084 in) |
| Ring side clearance (Top): | 0.030-0.070 mm (0.0012-0.0028 in) |
| Ring side clearance (Second): | 0.020-0.060 mm (0.0008-0.0024 in) |
| Ring-to-groove side clearance (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) |
| Ring end gap (Second): | 0.347-0.594 mm (0.0137-0.0234 in) |
| Ring width (Top): | 1.470-1.490 mm (0.0579-0.0587 in) |
| Ring width (Second): | 1.470-1.490 mm (0.0579-0.0587 in) |
| Connecting rod small end inner diameter | 18.010-18.015 mm (0.7090-0.7092 in) |
| Connecting rod big end inner diameter | 30.021-30.026 mm (1.1819-1.1821 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, gear driven |
| Valves: | 2 |
| Valve head diameter (INTAKE): | 25.000 mm (0.9842 in) |
| Valve head diameter (EXHAUST): | 24.000 mm (0.9449 in) |
| Valve seat angle (INTAKE): | 89.5-90.0° |
| Valve seat angle (EXHAUST): | 89.5-90.0° |
| Valve face angle (INTAKE): | 90.0-90.5° |
| Valve face angle (EXHAUST): | 90.0-90.5° |
| Valve steam diameter (INTAKE): | 5.500 mm (0.2165 in) |
| Valve steam diameter (EXHAUST): | 5.500 mm (0.2165 in) |
| Valve length (INTAKE): | 64.000 mm (2.5197 in) |
| Valve length (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 Data
| Valve lash | |
| Intake valve lash | 0.100 mm (0.0040 in) |
| Exhaust valve lash | 0.150 mm (0.0060 in) |
| Oil system | |
| Lubrication system: | Splash type |
| Oil type: | API SJ or higher |
| Recommended oil: | SAE 10W-30, 10W-40 |
| Oil capacity: | 0.6 liters (0.7 US.qts, 0.58 Imp. qts) |
| Ignition system | |
| Type: | Dependable electronic magneto |
| Spark plug: | Champion RC12YC |
| Spark plug gap | 0.76 mm (0.030 in) |
| Spark plug torque: | 27.0 Nm (2.75 kg·m; 20.0 lb·ft) |
| Ignition coil air gap | 0.254 mm (0.0100 in) |
References
1. Kohler 2000, RH series: RH255, RH265 service manual. Kohler Co. 2021.
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