Honda G42

The Honda G42 is a 171 cc (10.4 cu-in) single-cylinder, air-cooled, four-stroke cycle, internal combustion small gasoline engine manufactured by Honda Motor Company since 1972 for general-purpose applications.

The Honda G42 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.

The G42 engine a compression ratio rating is 6.4:1, cylinder bore and piston stroke are 66.0 mm (2.6 in) and 50.0 mm (2.0 in), respectively.

The G42 produced 3.3 PS (2.42 KW; 3.2 HP) at 3,400 rpm of continuous rated horsepower, 4.5 PS (3.31 KW; 4.4 HP) at 4,000 rpm of maximum horsepower and 8.3 Nm (0.85 kg·m; 6.13 lbf·ft) at 3,600 rpm of peak torque.

General information

Engine Specifications
Model	G42
Type	4-stroke, sidevalve type (L-head), single cylinder
Displacement	171 cm 3 (10.4 cu-in)
Max. horsepower	4.5 PS (3.31 KW; 4.4 HP) at 4,000 rpm
Max. torque	8.3 Nm (0.85 kg·m; 6.13 lbf·ft) at 3,600 rpm
Carburetor	Horizontal, butterfly valve
Cooling system	Forced-air
Ignition system	High voltage ignition
Lubricating system	Splash type
Starting system	Recoil starter
Stoping system	Ground switch
Fuel used	Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity	G42: 3.4 liters (0.9 US gal, 0.7 Imp. gal) G42K1: 4.0 liters (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)

Dimensions and Weight

	G42 K1
Length, mm (in)	425 (16.7)
Width, mm (in)	325 (12.8)
Height, mm (in)	430 (16.9)
Dry weight, kg (lb)	19.0 (41.9)

Cylinder Block and Head

Cylinder block
Compression ratio:		6.4:1
Bore x Stroke		66 x 50 mm (2.6 in x 2.0 in in)
Sleeve internal diameter		66.00 mm (2.59 in)
Piston skirt outer diameter		65.97-65.99 mm (2.59-2.60 in)
Number of piston rings (compression / oil):		2 / 1
Piston ring side clearance (Top):		0.030-0.070 mm (0.001-0.003 in)
Piston ring side clearance (Second):		0.030-0.070 mm (0.001-0.003 in)
Piston ring side clearance (Oil):		0.030-0.070 mm (0.001-0.003 in)
Piston ring end gap (Top):		0.200-0.400 mm (0.008-0.016 in)
Piston ring end gap (Second):		0.200-0.400 mm (0.008-0.016 in)
Piston ring end gap (Oil):		0.200-0.400 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
Valve stem outer diameter (INTAKE):		6.970 mm (0.274 in)
Valve stem outer diameter (EXHAUST):		6.925 mm (0.272 in)
Valve guide inner diameter (INTAKE):		7.000 mm (0.276 in)
Valve guide inner diameter (EXHAUST):		7.000 mm (0.276 in)
Spring free length		27.9 mm (1.1 in)
Camshaft journal diameter:		11.953-11.968 mm (0.470-0.471 in)

Maintenance data

Engine
Cylinder compression	6.0 kg/cm2 at 1,000 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 liters (0.63 US.qts, 0.53 Imp. qts)
Ignition system
Spark plug	G42: NGK B-6HS G42K1: 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
Others
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