Subaru-Robin EX40D

Subaru-Robin EX40DThe 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
Type4-stroke, OHC, single cylinder
Displacement404 cm 3 (24.65 cu-in)
Max. horsepower14.0 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
CarburetorHorizontal draft, float type carburetor
Cooling systemForced-air
Ignition systemTransistorized magneto ignition
Lubricating systemSplash
Starting systemRecoil or electric starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity7.0 L (1.85 US. gal. 1.54 Imp. gal.)
PTO shaft rotationCounterclockwise (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 Stroke89.0 mm x 65.0 mm (3.5 x 2.56 in)
Sleeve internal diameter89.000-89.022 mm (3.5039-3.5048 in)
Piston skirt outer diameter88.980-89.000 mm (3.5031-3.5039 in)
Number of piston rings (compression / oil):1 / 1
Ring side clearanceTop0.050-0.080 mm (0.002-0.0031 in)
Oil0.030-0.125 mm (0.0012-0.0049 in)
Ring end gapTop0.10-0.25 mm (0.0039-0.0098 in)
Oil0.15-0.55 mm (0.0059-0.0217 in)
Connecting rod small end ID21.010-21.023 mm (0.8272-0.8277 in)
Connecting rod big end ID38.000-38.016 mm (1.4961-1.4967 in)
Piston pin outer diameter20.992-21.000 mm (0.8265-0.8268 in)
Crankshaft crankpin outer diameter37.956-37.970 mm (1.4943-1.4949 in)
Crankshaft main journal diameter34.986-34.997 mm (1.3774-1.3778 in)/td>
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHC
Stem outer diameter (standard):INTAKE5.970-5.985 mm (0.235-0.2356 in)
EXHAUST5.970-5.985 mm (0.235-0.2356 in)
Valve spring free length:36.5 mm (1.437 in)
Camshaft lobe height:INTAKE35.658-35.758 mm (1.4039-1.4078 in)
EXHAUST39.408-39.508 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 bolt17-19 Nm; 1.7-1.9 kg·m; 12.3-13.7 ft·lb
Connecting rod bolt22-27 Nm; 2.2-2.7 kg·m; 16.3-19.9 ft·lb
Main bearing cover bolts22-24 Nm; 2.2-2.4 kg·m; 16.2-17.7 ft·lb
Flywheel nut100-120 Nm; 10.0-12.0 kg·m; 72.3-86.8 ft·lb

Service Information

Cylinder compression4.5 kg/cm2
Valve clearance
Intake valve clearance0.12-0.15 mm (0.0047-0.0059 in)
Exhaust valve clearance0.12-0.15 mm (0.0047-0.0059 in)
Oil system
Oil type4-stroke or an equivalent (SE or SF)
Recommended oilSAE 10W-30
Oil capacity1.2 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 gap0.6-0.7 mm (0.0236-0.0276 in)
Spark plug torque:25 N·m (2.5 kg·m, 18.4 ft·lb)
Ignition coil air gap0.3-0.5 mm (0.0118-0.0118 in)
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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