Honda G42

Honda G42 engineThe Honda G42 is a 171 cc, (10.44 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Honda Motor Company from 1972 for general-purpose applications.

The Honda G42 engine has a single-cylinder, slide valve (L-head) design, and camshaft driven by a single row chain driven by the crankshaft. It used a recoil starter, horizontal carburetor with butterfly valve, and high voltage ignition system. The engine is fitted with an oil bath-type air cleaner and a 3.4 L (0.9 US. gal. 0.75 Imp. gal.) fuel tank.

The G42 engine produced 3.3 PS (2.42 kW; 3.2 HP) at 3,400 rpm of continuous rated power, 4.5 PS (3.3 kW; 4.4 HP) at 4,000 rpm of maximum horsepower, and 8.3 N·m (0.8 kg·m, 6.1 ft·lb) at 3,600 rpm of peak torque.

General information

Engine Specifications
Engine modelG42
Engine type4-stroke, L-head, single-cylinder
Displacement171 cm3, (10.44 cu·in)
Max. horsepower4.5 PS (3.3 kW; 4.4 HP) at 4,000 rpm
Max. torque8.3 N·m (0.8 kg·m, 6.1 ft·lb) at 3,600 rpm
Cooling systemForced air
Air cleanerOil bath type
Lubricating systemSplash type
Ignition systemHigh-voltage ignition
Fuel systemHorizontal type carburetor with butterfly valve
Fuel consumption300 g/HPh
Fuel tank capacity G42 – 3.4 L (0.9 US gal. 0.7 Imp. gal.)
G42K1 – 4.0 L (1.1 US gal. 0.9 Imp. gal.)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemRecoil starter
Stoping systemIgnition primary circuit ground
GovernorCentrifugal govervor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)425 x 325 x 430 mm (16.7 x 12.8 x 16.9 in)
Dry weight19.0 kg (41.9 lbs)

Cylinder Block and Head

It has a 66.0 mm (2.6 in) cylinder bore and 50.0 mm (1.97 in) piston stroke. The compression ratio rating is 6.4:1.

Cylinder block
Compression ratio:6.4:1
Cylinder bore:66.0 mm (2.6 in)
Piston stroke:50.0 mm (1.97 in)
Cylinder internal diameter (standard):66.000 mm (2.5984 in)
Piston skirt outer diameter (standard):65.970-65.980 mm (2.5972-2.5976 in)
Number of piston rings (compression / oil):2/1
Connecting rod small end diameter (standard):18.010-18.030 mm (0.7091-0.7098 in)
Piston pin diameter:17.994-18.000 mm (0.7084-0.7087 in)
Side clearance (Top):0.030-0.070 mm (0.0012-0.0028 in)
Side clearance (Second):0.030-0.070 mm (0.0012-0.0028 in)
Side clearance (Oil):0.030-0.070 mm (0.0012-0.0028 in)
Ring end gap (Top):0.200-0.400 mm (0.0079-0.0157 in)
Ring end gap (Second):0.200-0.400 mm (0.0079-0.0157 in)
Ring end gap (Oil):0.200-0.400 mm (0.0079-0.0157 in)
Cylinder head
Valve arrangement:L-head
Valve steam diameter (INTAKE):6.970 mm (0.2744 in)
Valve steam diameter (EXHAUST):6.925 mm (0.2726 in)
Valve spring free length (INTAKE):27.9 mm (1.0984 in)
Valve spring free length (EXHAUST):27.9 mm (1.0984 in)
Camshaft lobe lift (INTAKE):5.8 mm (0.2283 in)
Camshaft lobe liift (EXHAUST):5.8 mm (0.2283 in)
Camshaft journal diameter:11.953-11.968 mm (0.4706-0.4712 in)

Service Data

The Honda 4-stroke or an equivalent oil with a viscosity of SAE 10W-30 or 10W-40 is recommended for the Honda G42 engine, refilling oil capacity is 0.6 L (0.63 US. qt, 0.53 Imp. qt.).

Compression pressure
Standard:0.6 kg/cm2
Valve clearance
Intake valve clearance:0.07 mm (0.0028 in)
Exhaust valve clearance:0.07 mm (0.0028 in)
Oil system
Lubrication system:Splash type
Oil type:SAE 10W-30 or 10W-40
Recommended oil:Honda 4-stroke or an equivalent
Oil capacity:0.6 L (0.63 US. qt, 0.53 Imp. qt.)
Fuel system
Type:Horizontal type carburetor with butterfly valve
Ignition system
Type:High-voltage ignition
Ignition type:20° B.T.D.C.
Spark plug: G42 – NGK: B-6HS
G42K1 – NGK: B-6HS, BR-6HS
Spark plug gap:0.6-0.7 mm (0.0236-0.0276 in)


Manufacturer or BrandModels
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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