Subaru-Robin EX40D

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)