The Robin-Subaru EX21D is a 0.2 L (211 cc, 12.88 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by the Industrial Products division of Subaru Corporation for general-purpose applications.
The Subaru EX21D engine has a single-cylinder, heavy-duty chain-driven overhead camshaft (OHC) system, a sophisticated mechanical compression release system, and a heavy-duty recoil starter. This engine used a horizontal draft, float type carburetor, transistorized magneto ignition system, splash type lubricating system, and forced-air cooling system. The EX21D is equipped with a 3.6 L (0.95 US. gal. 0.79 Imp. gal.) fuel tank.
The Subaru EX21D engine produced 7.0 PS (5.1 kW; 6.9 HP) at 4,000 rpm of maximum output power and 13.9 N·m (1.4 kg·m, 10.2 ft·lb) at 2,500 rpm of peak torque.
General information
| Engine Specifications | |
| Engine model | Robin-Subaru EX21D |
| Engine type | 4-stroke, OHC, single-cylinder |
| Displacement | 211 cm3, (12.88 cu·in) |
| Max. horsepower | 7.0 PS (5.1 kW; 6.9 HP) at 4,000 rpm |
| Max. torque | 13.9 N·m (1.4 kg·m, 10.2 ft·lb) at 2,500 rpm |
| Cooling system | Forced air |
| Lubricating system | Splash type |
| Ignition system | Transistorized magneto ignition |
| Fuel system | Horizontal draft, float type carburetor |
| Fuel tank capacity | 3.6 L (0.95 US. gal. 0.79 Imp. gal.) |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Starting system | Recoil or electric starter (option) |
| Stoping system | Ignition primary circuit ground |
| Governor | Centrifugal govervor |
| Charging capacity | 12-1A, 3A, 16.7A (option) |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Dimensions (L x W X H) | 311 x 366 x 336 mm (12.2 x 14.4 x 13.2 in) |
| Dry weight | 16.0 kg (35.3 lbs) |
Cylinder Block and Head
It has a 67.0 mm (2.64 in) cylinder bore and 60.0 mm (2.36 in) piston stroke. Compression ratio rating is 8.5:1. The engine uses cast iron cylinder liner and large ball bearings on both ends of crankshaft for maximum stability under demanding loads. The piston is equipped with single oil and two compression rings.
| Cylinder block | |
| Compression ratio: | 8.5:1 |
| Cylinder bore: | 67.0 mm (2.64 in) |
| Piston stroke: | 60.0 mm (2.36 in) |
| Cylinder internal diameter (standard): | 67.000-67.019 mm (2.6378-2.6385 in) |
| Piston skirt outer diameter (standard): | 66.960-67.000 mm (2.6362-2.6378 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Connecting rod big end diameter (standard): | 30.000-30.016 mm (1.1811-1.1817 in) |
| Connecting rod small end diameter (standard): | 16.010-16.021 mm (0.6303-0.6307 in) |
| Piston pin diameter: | 15.992-16.000 mm (0.6296-0.6299 in) |
| Side clearance (Top): | 0.035-0.080 mm (0.0014-0.0031 in) |
| Side clearance (Second): | 0.035-0.080 mm (0.0014-0.0031 in) |
| Side clearance (Oil): | 0.010-0.065 mm (0.0004-0.0026 in) |
| Ring end gap (Top): | 0.15-0.30 mm (0.0059-0.0118 in) |
| Ring end gap (Second): | 0.20-0.40 mm (0.0079-0.0157 in) |
| Ring end gap (Oil): | 0.05-0.25 mm (0.002-0.0098 in) |
| Crankshaft main journal diameter №1: | 27.988-24.997 mm (1.1019-0.9841 in) |
| Crankshaft main journal diameter №2: | 24.988-24.997 mm (0.9838-0.9841 in) |
| Crankpin journal diameter: | 29.967-29.980 mm (1.1798-1.1803 in) |
| Crankshaft center distance: | 30 mm (1.18 in) |
| Cylinder head | |
| Valve arrangement: | OHC |
| Valves: | 2 |
| Valve steam diameter (INTAKE): | 5.440-5.455 mm (0.2142-0.2148 in) |
| Valve steam diameter (EXHAUST): | 5.425-5.445 mm (0.2136-0.2144 in) |
| Valve spring free length (INTAKE): | 27.4 mm (1.0787 in) |
| Valve spring free length (EXHAUST): | 27.4 mm (1.0787 in) |
| Camshaft lobe height (INTAKE): | 29.028-29.128 mm (1.1428-1.1468 in) |
| Camshaft lobe height (EXHAUST): | 29.028-29.128 mm (1.1428-1.1468 in) |
Tightening torque
| Tightening torque settings | |
| Cylinder head M8 × 68 flange bolt (Re-use): | 25-27 Nm; 2.5-2.7 kg·m; 18.1-19.5 ft·lb |
| Cylinder head M8 × 68 flange bolt (New): | 28-30 Nm; 2.8-3.0 kg·m; 20.3-21.7 ft·lb |
| Cylinder head M8 × 35 flange bolt: | 17-19 Nm; 1.7-1.9 kg·m; 12.3-13.7 ft·lb |
| Connecting rod bolt: | 13-15 Nm; 1.3-1.5 kg·m; 9.4-10.8 ft·lb |
| Main bearing cover bolts: | 22-24 Nm; 2.2-2.4 kg·m; 16.2-17.7 ft·lb |
| Flywheel nut: | 59-64 Nm; 5.9-6.4 kg·m; 42.7-46.3 ft·lb |
Service Data
The 4-stroke engine oil, API service classification SE oil with a viscosity of SAE 10W-30 or 10W-40 is recommended for the EX21D, refilling oil capacity is 0.6 L (0.63 US. qt, 0.53 Imp. qt.). Recommended spark plug are NGK: BR-6HS or CHAMPION RL86C with 0.6-0.7 mm (0.0236-0.0276 in) spark plug gap.
The valve clearance is 0.12-0.15 mm (0.0047-0.0059 in) for intake valves and 0.12-0.15 mm (0.0047-0.0059 in) for exhaust valves. Standard cylinder compression is 3.5 kg/cm2 at 500 rpm.
| Cylinder compression: | 3.5 kg/cm2 at 500 rpm |
| Valve clearance | |
| Intake valve clearance: | 0.12-0.15 mm (0.0047-0.0059 in) |
| Exhaust valve clearance: | 0.12-0.15 mm (0.0047-0.0059 in) |
| Oil system | |
| Lubrication system: | Splash type |
| Oil consupumtion: | 5-10 ml/h |
| Oil type: | 4-stroke engine oil, API service classification SE |
| Recommended oil: | SAE 10W-30 or 10W-40 |
| Oil capacity: | 0.6 L (0.63 US. qt, 0.53 Imp. qt.) |
| Fuel system | |
| Type: | Horizontal draft, float type carburetor |
| Ignition system | |
| Type: | Transistorized magneto ignition |
| Spark plug: | NGK: BR-6HS; CHAMPION: RL86C |
| Spark plug gap: | 0.6-0.7 mm (0.0236-0.0276 in) |
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