The Subaru-Robin EX40D is a 404 cc (24.65 cu·in) single-cylinder air-cooled 4-stroke internal combustion small gasoline engine manufactured by Industrial Products division of Subaru Corporation for general-purpose applications.
The Subaru-Robin EX40D engine has an OHС (overhead camshaft) design; high compression ratio for better fuel efficiency; horizontal draft, float type carburetor; recoil starter or electric starter as option and transistorized magneto ignition system.
An 89.0 mm (3.5 in) cylinder bore and 65.0 mm (2.56 in) piston stroke give the motor a total 404 cc (24.65 cu-in) of displacement. Compression ratio rating is 8.3:1. The engine produced 14.0 PS (10.3 kW; 13.8 HP) at 3,600 rpm of maximum horsepower and 8.6 PS (6.3 kW; 8.4 HP) at 3,000 rpm or 9.5 PS (7.0 kW; 9.4 HP) at 3,600 rpm of continuous output power. Peak torque is 27.0 Nm (2.75 kg·m; 19.93 ft·lb) at 2,400 rpm.
General information
| Engine Specifications | |
| Model | EX40D |
| Type | 4-stroke, OHC, single cylinder |
| Displacement | 404 cm 3 (24.65 cu-in) |
| Max. horsepower | 14.0 PS (10.3 kW; 13.8 HP) at 3,600 rpm |
| Max. torque (crank PTO) | 27.0 Nm (2.75 kg·m; 19.93 ft·lb) at 2,400 rpm |
| Carburetor | Horizontal draft, float type carburetor |
| Cooling system | Forced-air |
| Ignition system | Transistorized magneto ignition |
| Lubricating system | Splash |
| Starting system | Recoil or electric starter |
| Stoping system | Ignition primary circuit ground |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 7.0 L (1.85 US. gal. 1.54 Imp. gal.) |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
Cylinder Block and Head
The EX40D has cast iron cylinder sleeve, ball bearing supported forged steel crankshaft, improved piston design. The piston has single compression rings and a single oil ring.
| Cylinder block | ||
| Bore x Stroke | 89.0 mm x 65.0 mm (3.5 x 2.56 in) | |
| Sleeve internal diameter | 89.000-89.022 mm (3.5039-3.5048 in) | |
| Piston skirt outer diameter | 88.980-89.000 mm (3.5031-3.5039 in) | |
| Number of piston rings (compression / oil): | 1 / 1 | |
| Ring side clearance | Top | 0.050-0.080 mm (0.002-0.0031 in) |
| 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) |
| Oil | 0.15-0.55 mm (0.0059-0.0217 in) | |
| Connecting rod small end ID | 21.010-21.023 mm (0.8272-0.8277 in) | |
| Connecting rod big end ID | 38.000-38.016 mm (1.4961-1.4967 in) | |
| Piston pin outer diameter | 20.992-21.000 mm (0.8265-0.8268 in) | |
| Crankshaft crankpin outer diameter | 37.956-37.970 mm (1.4943-1.4949 in) | |
| Crankshaft main journal diameter | 34.986-34.997 mm (1.3774-1.3778 in)/td> | |
| Cylinder Head | ||
| Warpage (limit) | 0.10 mm (0.004 in) | |
| Valve Arrangement: | OHC | |
| Valves: | 2 | |
| Stem outer diameter (standard): | INTAKE | 5.970-5.985 mm (0.235-0.2356 in) |
| EXHAUST | 5.970-5.985 mm (0.235-0.2356 in) | |
| Valve spring free length: | 36.5 mm (1.437 in) | |
| Camshaft lobe height: | INTAKE | 35.658-35.758 mm (1.4039-1.4078 in) |
| EXHAUST | 39.408-39.508 mm (1.5515-1.5554 in) | |
Tightening torque specs
| Tightening torque specs | |
| 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 Information
| Engine | |
| Cylinder compression | 4.5 kg/cm2 |
| 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 | |
| Oil type | 4-stroke or an equivalent (SE or SF) |
| 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 | |
| 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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