Subaru-Robin EX21D

Subaru-Robin EX21D engineThe Robin-Subaru EX21D is a 0.2 L (211 cc, 12.88 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 Subaru EX21D engine has a single-cylinder, heavy-duty chain-driven overhead camshaft (OHC) system, a sophisticated mechanical compression release system, and a heavy-duty recoil starter. This engine used a horizontal draft, float type carburetor, transistorized magneto ignition system, splash type lubricating system, and forced-air cooling system. The EX21D is equipped with a 3.6 L (0.95 US. gal. 0.79 Imp. gal.) fuel tank.

The Subaru EX21D engine produced 7.0 PS (5.1 kW; 6.9 HP) at 4,000 rpm of maximum output power and 13.9 N·m (1.4 kg·m, 10.2 ft·lb) at 2,500 rpm of peak torque.

General information

Engine Specifications
Engine modelRobin-Subaru EX21D
Engine type4-stroke, OHC, single-cylinder
Displacement211 cm3, (12.88 cu·in)
Max. horsepower7.0 PS (5.1 kW; 6.9 HP) at 4,000 rpm
Max. torque13.9 N·m (1.4 kg·m, 10.2 ft·lb) at 2,500 rpm
Cooling systemForced air
Lubricating systemSplash type
Ignition systemTransistorized magneto ignition
Fuel systemHorizontal draft, float type carburetor
Fuel tank capacity3.6 L (0.95 US. gal. 0.79 Imp. gal.)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemRecoil or electric starter (option)
Stoping systemIgnition primary circuit ground
GovernorCentrifugal govervor
Charging capacity12-1A, 3A, 16.7A (option)
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)311 x 366 x 336 mm (12.2 x 14.4 x 13.2 in)
Dry weight16.0 kg (35.3 lbs)

Cylinder Block and Head

It has a 67.0 mm (2.64 in) cylinder bore and 60.0 mm (2.36 in) piston stroke. Compression ratio rating is 8.5:1. 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 two compression rings.

Cylinder block
Compression ratio:8.5:1
Cylinder bore:67.0 mm (2.64 in)
Piston stroke:60.0 mm (2.36 in)
Cylinder internal diameter (standard):67.000-67.019 mm (2.6378-2.6385 in)
Piston skirt outer diameter (standard):66.960-67.000 mm (2.6362-2.6378 in)
Number of piston rings (compression / oil):2/1
Connecting rod big end diameter (standard):30.000-30.016 mm (1.1811-1.1817 in)
Connecting rod small end diameter (standard):16.010-16.021 mm (0.6303-0.6307 in)
Piston pin diameter:15.992-16.000 mm (0.6296-0.6299 in)
Side clearance (Top):0.035-0.080 mm (0.0014-0.0031 in)
Side clearance (Second):0.035-0.080 mm (0.0014-0.0031 in)
Side clearance (Oil):0.010-0.065 mm (0.0004-0.0026 in)
Ring end gap (Top):0.15-0.30 mm (0.0059-0.0118 in)
Ring end gap (Second):0.20-0.40 mm (0.0079-0.0157 in)
Ring end gap (Oil):0.05-0.25 mm (0.002-0.0098 in)
Crankshaft main journal diameter №1:27.988-24.997 mm (1.1019-0.9841 in)
Crankshaft main journal diameter №2:24.988-24.997 mm (0.9838-0.9841 in)
Crankpin journal diameter:29.967-29.980 mm (1.1798-1.1803 in)
Crankshaft center distance:30 mm (1.18 in)
Cylinder head
Valve arrangement:OHC
Valve steam diameter (INTAKE):5.440-5.455 mm (0.2142-0.2148 in)
Valve steam diameter (EXHAUST):5.425-5.445 mm (0.2136-0.2144 in)
Valve spring free length (INTAKE):27.4 mm (1.0787 in)
Valve spring free length (EXHAUST):27.4 mm (1.0787 in)
Camshaft lobe height (INTAKE):29.028-29.128 mm (1.1428-1.1468 in)
Camshaft lobe height (EXHAUST):29.028-29.128 mm (1.1428-1.1468 in)

Tightening torque

Tightening torque settings
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:13-15 Nm; 1.3-1.5 kg·m; 9.4-10.8 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 Data

The 4-stroke engine oil, API service classification SE oil with a viscosity of SAE 10W-30 or 10W-40 is recommended for the EX21D, refilling oil capacity is 0.6 L (0.63 US. qt, 0.53 Imp. qt.). Recommended spark plug are NGK: BR-6HS or CHAMPION RL86C 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 3.5 kg/cm2 at 500 rpm.

Cylinder compression:3.5 kg/cm2 at 500 rpm
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
Lubrication system:Splash type
Oil consupumtion:5-10 ml/h
Oil type:4-stroke engine oil, API service classification SE
Recommended oil:SAE 10W-30 or 10W-40
Oil capacity:0.6 L (0.63 US. qt, 0.53 Imp. qt.)
Fuel system
Type:Horizontal draft, float type carburetor
Ignition system
Type:Transistorized magneto ignition
Spark plug:NGK: BR-6HS;
Spark plug gap:0.6-0.7 mm (0.0236-0.0276 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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We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.

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