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
Model G50
Type 4-stroke, side valve type (L-head), single cylinder
Displacement 187 cm 3 (11.4 cu-in)
Max. horsepower 5.0 PS (3.67 kW) at 4000 rpm
Max. torque 9.0 Nm (0.92 kg·m) at 3600 rpm
Carburetor Horizontal, butterfly valve
Cooling system Forced-air
Ignition system High voltage ignition
Lubricating system Splash system
Starting system Recoil starter
Stoping system Ground switch
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity G50 – 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 consumption 300 g/HPh (0.67 lb/HPh)
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio: G50K1 – 6.5:1
G50K2 – 6.9:1
Bore x Stroke 69 x 50 mm (2.7 in x 2.0 in in)
Sleeve internal diameter 69.00 mm (2.71 in)
Piston skirt outer diameter 68.97-68.99 mm (2.5492-2.5558 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top/second/oil 0.02-0.06 mm (0.008-0.024 in)
Ring end gap Top/second/oil 0.2-0.4 mm (0.008-0.016 in)
Connecting rod small end ID 18.01-18.03 mm (0.708-0.711 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: Side valve type (L-head)
Valves: 2
Stem outer diameter (standard): INTAKE 6.970 mm (0.274 in)
EXHAUST 6.925 mm (0.272 in)
Guide internal diameter INTAKE / EXHAUST 7.000 mm (0.276 in)
Spring free length 27.9 mm (1.1 in)
Camshaft journal diameter: 11.966-11.984 mm (0.4711-0.4718 in)
Cylinder compression G50K1 – 7.0 kg/cm2 at 750 rpm
G50K2 – 6.0 kg/cm2 at 1000 rpm
Adjust timing ignition
Ignition timing 20° B.T.D.C. (Fixed)
Adjust valve clearance
Intake valve 0.07 mm (0.003 in)
Exhaust valve 0.07 mm (0.003 in)
Oil system
Oil type Honda 4-stroke
Recommended oil 10W-40
Oil capacity 0.6 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 gap 0.6-0.7 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, nut 3.5-6.5 Nm; 0.35-0.65 kg·m; 2.5-4.7 ft·lb
6×1.0 mm bolt 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
8×1.25 mm bolt 20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb
10×1.25 mm bolt 40-50 Nm; 4.0-5.0 kg·m; 28.9-36.2 ft·lb
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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    • Managed to repaor mine with a bike tube repairkit… works since 8 yrs. But also interested in a new one

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