Honda G42

Honda G42 engineThe Honda G42 is a 171 cc single-cylinder air-coolled 4-stroke 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) at 3400 rpm of continuous rated horsepower and 4.5 PS (3.31 kW) at 4000 rpm of maximum horsepower.

General information

Engine Specifications
Type4-stroke, side valve type (L-head), single cylinder
Displacement171 cm 3 (10.4 cu-in)
Max. horsepower4.5 PS (3.31 kW) at 4000 rpm
Max. torque8.3 Nm (0.85 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 capacityG42 – 3.4 L (0.9 US gal. 0.7 Imp. gal.)
G42K1 – 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)

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 Stroke66 x 50 mm (2.6 in x 2.0 in in)
Sleeve internal diameter66.00 mm (2.59 in)
Piston skirt outer diameter65.97-65.99 mm (2.59-2.60 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop/second/oil0.03-0.07 mm (0.001-0.003 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:11.953-11.968 mm (0.470-0.471 in)

Maintenance data

Cylinder compression6.0 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 G42 – NGK: B-6HS
G42K1 – 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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