Honda G50

Honda G50 engineThe Honda G50 is a 187 cc 11.4 cu-in) single-cylinder air-coolled 4-stroke internal combustion small gasoline engine manufactured by Honda Motor Company or general-purpose applications.

The Honda G50 engine has a slide valve (L-head) design and camshaft driven by a single row chain driven by the crankshaft. It has a recoil starter, horizontal carburetor with butterfly valve and high voltage ignition.

Cylinder bore and piston stroke are 69.0 mm (2.7 in) and 50.0 mm (2.0 in), respectively. Compression ratio rating is 6.5:1 for G50K1 and 6.9:1 for G50K2

The G50 produced 3.8 PS (2.8 kW) at 3600 rpm of continuous rated horsepower and 5.0 PS (3.67 kW) at 4000 rpm of maximum horsepower. The Honda G50 produced 9.0 Nm (0.85 kg·m) at 3600 rpm of torque.

General information

Engine Specifications
Type4-stroke, side valve type (L-head), single cylinder
Displacement187 cm 3 (11.4 cu-in)
Max. horsepower5.0 PS (3.67 kW) at 4000 rpm
Max. torque9.0 Nm (0.92 kg·m) at 3600 rpm
CarburetorHorizontal, butterfly valve
Cooling systemForced-air
Ignition systemHigh voltage ignition
Lubricating systemSplash system
Starting systemRecoil starter
Stoping systemGround switch
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacityG50 – 6.0 L (1.6 US gal. 1.3 Imp. gal.)
G50K1 – 3.4 L (0.9 US gal. 0.7 Imp. gal.)
G50K2 – 4.0 L (1.1 US gal. 0.9 Imp. gal.)
Fuel consumption300 g/HPh (0.67 lb/HPh)
PTO shaft rotationCounterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio:G50K1 – 6.5:1
G50K2 – 6.9:1
Bore x Stroke69 x 50 mm (2.7 in x 2.0 in in)
Sleeve internal diameter69.00 mm (2.71 in)
Piston skirt outer diameter68.97-68.99 mm (2.5492-2.5558 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop/second/oil0.02-0.06 mm (0.008-0.024 in)
Ring end gapTop/second/oil0.2-0.4 mm (0.008-0.016 in)
Connecting rod small end ID18.01-18.03 mm (0.708-0.711 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:Side valve type (L-head)
Stem outer diameter (standard):INTAKE6.970 mm (0.274 in)
EXHAUST6.925 mm (0.272 in)
Guide internal diameterINTAKE / EXHAUST7.000 mm (0.276 in)
Spring free length27.9 mm (1.1 in)
Camshaft journal diameter:11.966-11.984 mm (0.4711-0.4718 in)
Cylinder compressionG50K1 – 7.0 kg/cm2 at 750 rpm
G50K2 – 6.0 kg/cm2 at 1000 rpm
Adjust timing ignition
Ignition timing20° B.T.D.C. (Fixed)
Adjust valve clearance
Intake valve0.07 mm (0.003 in)
Exhaust valve0.07 mm (0.003 in)
Oil system
Oil typeHonda 4-stroke
Recommended oil10W-40
Oil capacity0.6 l (0.6 US gal. 0.5 Imp. gal.)
Ignition system
Spark plug G50 – NGK: B-6H
G50K1 – NGK: B-6HS
G50K2 – NGK: B-6HS, BR-6HS
Spark plug gap0.6-0.7 mm (0.024-0.028 in)

Tightening torque specs

Tightening torque specs
Cylinder head (8×1.25 mm)20-24 Nm; 2.0-2.4 kg·m; 14.5-17.4 ft·lb
Flywheel (14×1.25 mm)80-90 Nm; 8.0-9.0 kg·m; 57.9-65.1 ft·lb
Fuel tank (6×1.0 mm)10-12 Nm; 1.0-1.2 kg·m; 7.2-8.7 ft·lb
Fuel tank (8×1.25 mm)24-28 Nm; 2.4-2.8 kg·m; 17.4-20.3 ft·lb
Muffler (6×1.0 mm)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Starter pulley (6×1.0 mm)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Fuel cock (6×1.0 mm)10-12 Nm; 1.0-1.2 kg·m; 7.2-8.7 ft·lb
PTO (8×1.25 mm)20-24 Nm; 2.0-2.4 kg·m; 14.5-17.4 ft·lb
Carburetor (6×1.0 mm)10-12 Nm; 1.0-1.2 kg·m; 7.2-8.7 ft·lb
5×0.8 mm screw, bolt, nut3.5-6.5 Nm; 0.35-0.65 kg·m; 2.5-4.7 ft·lb
6×1.0 mm bolt8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
8×1.25 mm bolt20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb
10×1.25 mm bolt40-50 Nm; 4.0-5.0 kg·m; 28.9-36.2 ft·lb
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    • Managed to repaor mine with a bike tube repairkit… works since 8 yrs. But also interested in a new one

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