Subaru-Robin EX27D

Subaru-Robin EX27DThe Subaru-Robin EX27D is a 265 cc (16.17 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 EX27D 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.

A 75.0 mm (2.95 in) cylinder bore and 60.0 mm (2.36 in) piston stroke give the motor a total 265 cc (16.17 cu-in) of displacement. Compression ratio rating is 8.3:1. The engine produced 9.0 PS (6.6 kW; 8.9 HP) at 4,000 rpm of maximum horsepower and 6.0 PS (4.4 kW; 5.9 HP) at 3,000 rpm or 6.9 PS (5.1 kW; 6.8 HP) at 3,600 rpm of continuous output power. Maximum torque is 18.6 N·m (1.9 kg·m, 13.7 ft·lb) at 2,500 rpm.

General information

Engine Specifications
Model EX27D
Type 4-stroke, OHC, single cylinder
Displacement 265 cm 3 (16.17 cu-in)
Max. horsepower 9.0 PS (6.6 kW; 8.9 HP) at 4,000 rpm
Max. torque (crank PTO) 18.6 N·m (1.9 kg·m, 13.7 ft·lb) at 2,500 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 6.1 L (1.61 US. gal. 1.34 Imp. gal.)
Fuel consumption 367 g/kWH
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

The EX27D has cast iron cylinder sleeve, ball bearing supported forged steel crankshaft, improved piston design. The piston has two compression rings and one oil ring.

Cylinder block
Compression ratio: 8.3:1
Bore x Stroke 75.0 x 60.0 mm (2.95 x 2.36 in)
Sleeve internal diameter 75.000-75.019 mm (2.9528-2.9535 in)
Piston skirt outer diameter 74.980-75.000 mm (2.952-2.9528 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top 0.035-0.080 mm (0.0014-0.0031 in))
Second 0.035-0.080 mm (0.0014-0.0031 in)
Oil 0.010-0.065 mm (0.0004-0.0026 in)
Ring end gap Top 0.10-0.30 mm (0.0039-0.0118 in)
Second 0.20-0.40 mm (0.0079-0.0157 in)
Oil 0.10-0.30 mm (0.0039-0.0118 in)
Connecting rod small end ID 18.010-18.020 mm (0.7091-0.7094 in)
Connecting rod big end ID 34.500-34.516 mm (1.3583-1.3589 in)
Piston pin outer diameter 17.992-18.000 mm (0.7083-0.7087 in)
Crankshaft crankpin outer diameter 34.467-34.480 mm (1.357-1.3575 in)
Crankshaft main journal diameter 29.998-29.997 mm (1.181-1.181 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHC
Valves: 2
Stem outer diameter (standard): INTAKE 5.440-5.455 mm (0.2142-0.2148 in)
EXHAUST 5.425-5.445 mm (0.2136-0.2144 in)
Valve spring free length: 27.4 mm (1.0787 in)
Camshaft lobe height: INTAKE 29.028-29.128 mm (1.1428-1.1468 in)
EXHAUST 29.028-29.128 mm (1.1428-1.1468 in)

Tightening torque specs

Tightening torque specs
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 17-20 Nm; 1.7-2.0 kg·m; 12.3-14.5 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 Information

Cylinder compression 3.5 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 1.0 L (1.06 US. qt, 0.88 Imp. qt.)
Ignition system
Spark plug NGK: BR-6HS;
Spark plug gap 0.6-0.7 mm (0.0236-0.0276 in)
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  1. If fuel was left in it, it is likely the carburetor is clogged up. Google search how to clean a Honda carburetor for info on how to clean it. And stop using gasahol (gasoline/alcohol fuel blend) in it… only burn straight gas. I’d suggest putting in a bit of Marine Stabil in the gasoline as well.

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