The Robin-Subaru EX40D is a 0.4 L (404 cc, 24.65 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 EX40D engine has a single-cylinder, heavy-duty chain-driven overhead camshaft (OHC) system, a sophisticated mechanical compression release system, and a recoil or electric starter. This engine used a horizontal draft, float type carburetor, transistorized magneto ignition system, splash type lubricating system, and forced-air cooling system. The EX40D is equipped with a 7.0 L (1.85 US. gal. 1.54 Imp. gal.) fuel tank.
The EX40D engine produced 12.0 PS (8.8 kW; 11.8 HP) at 3,600 rpm of maximum net power and 14.0 PS (10.3 kW; 13.8 HP) at 3,600 rpm of maximum gross power. Peak torque is 27.0 Nm (2.75 kg·m; 19.93 ft·lb) at 2,400 rpm.
General information
| Engine Specifications | |
| Engine model | Robin-Subaru EX40D |
| Engine type | 4-stroke, OHC, single-cylinder |
| Displacement | 404 cm3, (24.65 cu·in) |
| Max. horsepower | 12.0 PS (8.8 kW; 11.8 HP) at 3,600 rpm |
| Max. torque | 27.0 Nm (2.75 kg·m; 19.93 ft·lb) at 2,400 rpm |
| Cooling system | Forced air |
| Lubricating system | Splash type |
| Ignition system | Transistorized magneto ignition |
| Fuel system | Horizontal draft, float type carburetor |
| Fuel tank capacity | 7.0 L (1.85 US. gal. 1.54 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) | 389 x 450 x 447 mm (15.3 x 17.7 x 17.6 in) |
| Dry weight | 33.0 kg (72.8 lbs) |
Cylinder Block and Head
Cylinder bore and piston stroke are 89.0 mm (3.5 in) and 65.0 mm (2.56 in), respectively. Compression ratio rating is 8.3:1. 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 single compression rings.
| Cylinder block | |
| Compression ratio: | 8.3:1 |
| Cylinder bore: | 89.0 mm (3.5 in) |
| Piston stroke: | 65.0 mm (2.56 in) |
| Cylinder internal diameter (standard): | 89.000-89.022 mm (3.5039-3.5048 in) |
| Piston skirt outer diameter (standard): | 88.980-89.000 mm (3.5031-3.5039 in) |
| Number of piston rings (compression / oil): | 1/1 |
| Connecting rod big end diameter (standard): | 38.000-38.016 mm (1.4961-1.4967 in) |
| Connecting rod small end diameter (standard): | 21.010-21.023 mm (0.8272-0.8277 in) |
| Piston pin diameter: | 20.992-21.000 mm (0.8265-0.8268 in) |
| Side clearance (Top): | 0.050-0.080 mm (0.002-0.0031 in) |
| Side clearance (Oil): | 0.030-0.125 mm (0.0012-0.0049 in) |
| Ring end gap (Top): | 0.10-0.25 mm (0.0039-0.0098 in) |
| Ring end gap (Oil): | 0.15-0.55 mm (0.0059-0.0217 in) |
| Crankshaft main journal diameter: | 34.986-34.997 mm (1.3774-1.3778 in) |
| Crankpin journal diameter: | 37.956-37.970 mm (1.4943-1.4949 in) |
| Crankshaft center distance: | 32.5 mm (1.28 in) |
| Cylinder head | |
| Valve arrangement: | OHC, chain driven |
| Valves: | 2 |
| Valve steam diameter (INTAKE): | 5.970-5.985 mm (0.235-0.2356 in) |
| Valve steam diameter (EXHAUST): | 5.970-5.985 mm (0.235-0.2356 in) |
| Valve spring free length (INTAKE): | 36.5 mm (1.437 in) |
| Valve spring free length (EXHAUST): | 36.5 mm (1.437 in) |
| Camshaft lobe height (INTAKE): | 35.658-35.758 mm (1.4039-1.4078 in) |
| Camshaft lobe height (EXHAUST): | 39.408-39.508 mm (1.5515-1.5554 in) |
Tightening torque
| Tightening torque settings | |
| Cylinder head M10 × 75 flange bolt (Re-use): | 29-31 Nm; 2.9-3.1 kg·m; 21.0-22.4 ft·lb |
| Cylinder head M10 × 75 flange bolt (New): | 37-39 Nm; 3.7-3.9 kg·m; 26.7-28.2 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: | 22-27 Nm; 2.2-2.7 kg·m; 16.3-19.9 ft·lb |
| Main bearing cover bolts: | 22-24 Nm; 2.2-2.4 kg·m; 16.2-17.7 ft·lb |
| Flywheel nut: | 100-120 Nm; 10.0-12.0 kg·m; 72.3-86.8 ft·lb |
Service Data
The 4-stroke engine oil, API service classification SE oil with a viscosity of SAE 10W-30 is recommended for the EX40D, refilling oil capacity is 1.2 L (1.27 US. qt, 1.06 Imp. qt.). Recommended spark plug is NGK BR-6HS 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 4.5 kg/cm2 at 500 rpm.
| Cylinder compression | |
| Cylinder compression: | 4.5 kg/cm2 at 500 rpm |
| Valve clearance | |
| Intake valve clearance (COLD): | 0.12-0.15 mm (0.0047-0.0059 in) |
| Exhaust valve clearance (COLD): | 0.12-0.15 mm (0.0047-0.0059 in) |
| Oil system | |
| Lubrication system: | Splash type |
| Oil consupumtion: | 7-11 ml/h |
| Oil type: | 4-stroke engine oil, API service classification SE |
| Recommended oil: | SAE 10W-30 |
| Oil capacity: | 1.2 L (1.27 US. qt, 1.06 Imp. qt.) |
| Fuel system | |
| Type: | Horizontal draft, float type carburetor |
| Main jet: | URETHANE: 113; DUAL: 110 |
| Slow jet: | URETHANE: 49; DUAL: 51 |
| Ignition system | |
| Type: | Transistorized magneto ignition |
| Spark plug: | NGK BR-6HS |
| Spark plug gap: | 0.6-0.7 mm (0.0236-0.0276 in) |
| Spark plug torque: | 25 N·m (2.5 kg·m, 18.4 ft·lb) |
| Ignition coil air gap | 0.3-0.5 mm (0.0118-0.0118 in) |
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