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Honda G42 Engine

The Honda G42 is a 4-stroke L-head single cylinder horizontal shaft air-cooled gasoline engine from G-series. A 10.4 cu. in (171 cc) engine has a cylinder bore of 2.59" (66 mm), piston stroke of 1.97" (50 mm), and rated power of 4.4 Hp (3.3 kW) at 4000 rpm. The compression ratio rating is 6.4:1. The Honda G42 engine is equipped with a splash type lubrication, horizontal carburetor with butterfly valve, forced-air cooling system, and high voltage ignition system. The operating weight is 42 lbs (19 kg).

General Technical Data

Engine Specifications

Engine Model ................. Honda G42
Engine Type ................. 4-cycle L-head 1-cylinder air-cooled small gasoline
Number of Cylinders ................. Single
Displacement, cu.in (cc) ................. 10.4 (171)
Cylinder Bore, in (mm) ................. 2.59 (66.0)
Piston Stroke, in (mm) ................. 1.97 (50.0)
Rated Engine Power, hp (kW) ................. 4.4 (3.3)
Rated Engine Speed, rpm ................. 4000
Maximum Torque, Nm (ft-lbs) ................. 8.3 (6.1)
Torque Speed, rpm ................. 3600
Compression Ratio ................. 6.4:1
Lubrication System ................. Splash type
Cooling System ................. Forced air
Air Cleaner Type ................. Semi-dry
Ignition System ................. High voltage ignition
Starting System ................. Recoil starter
Electrical System Rating, Volts .................. 12

Fuel System

Fuel System Type ................. Carburetor
Carburetor Type ................. Horizontal with butterfly valve
Governor Type ................. Centrifugal
Fuel Consumption, g/HPh ................. 300
Fuel Type ................. Gasoline (86 or higher)
Fuel Tank Capacity, qts (L) ................. 3.6 (3.4)

Dimensions and Weight

Overall Length, in (mm) ................. 16.7 (425)
Overall Width, in (mm) ................. 12.8 (325)
Overall Height, in (mm) ................. 16.9 (430)
Net Weight, lbs (kg) ................. 41.9 (19.0)

Maintenance Data

Engine Oil

Engine Oil Type (Summer) ................. SAE 10W-40
Engine Oil Type (Winter) ................. SAE 10W
API Service Classifications ................. SE or higher
Oil Capacity, qts (L) ................. 0.65 (0.60)

Ignition System

Spark Plug Type ................. NGK BR6HS, B6HS
Spark Plug Gap, in (mm) ................. 0.0236-0.0276 (0.60-0.70)
Ignition Timing, deg ................. 20 BTDC
Spark Plug Torque, Nm (ft-lbs) ................. 20 (14.7)

Service Specifications

Cylinder Block

Cylinder Compression, psi (kPa) ................. 85 (585)
Cylinder Bore Inside Diameter (Std), in (mm) ................. 2.59 (66.00)
Cylinder Bore Inside Diameter (Wear Limit), in (mm) ................. 2.593 (66.10)
Connecting Rod Small End I.D, in (mm) .................. 0.708-0.711 (18.01-18.03)
Piston Skirt Outside Diameter, in (mm) ................. 2.59-2.60 (65.97-65.99)
Top Ring Side Clearance, in (mm) .................. 0.001-0.003 (0.030-0.070)
Middle Ring Side Clearance, in (mm) .................. 0.001-0.003 (0.030-0.070)
Oil Ring Side Clearance, in (mm) .................. 0.001-0.003 (0.030-0.070)
Top Ring End Gap, in (mm) .................. 0.008-0.016 (0.20-0.40)
Middle Ring End Gap, in (mm) .................. 0.008-0.016 (0.20-0.40)
Oil Ring End Gap, in (mm) .................. 0.008-0.016 (0.20-0.40)

Cylinder Head and Valves

Cylinder Head (Max Out of Flatness), in (mm) ................. 0.004 (0.10)
Intake Valve Clearance, in (mm) ................. 0.003-0.006 (0.076-0.152)
Exhaust Valve Clearance, in (mm) ................. 0.003-0.006 (0.076-0.152)
Intake Valve Stem Outside Diameter (Std), in (mm) ................. 0.274 (6.97)
Intake Valve Stem Outside Diameter (Wear Limit), in (mm) ................. 0.272 (6.91)
Exhaust Valve Stem Outside Diameter (Std), in (mm) ................. 0.273 (6.925)
Exhaust Valve Stem Outside Diameter (Wear Limit), in (mm) ................. 0.271 (6.89)
Intake Valve Guide Inside Diameter, in (mm) ................. 0.276 (7.00)
Exhaust Valve Guide Inside Diameter, in (mm) ................. 0.276 (7.00)
Intake Valve Stem to Valve Guide Clearance, in (mm) .................. 0.0012-0.0023 (0.030-0.060)
Exhaust Valve Stem to Valve Guide Clearance, in (mm) .................. 0.0030-0.0041 (0.075-0.105)
Intake Valve Spring Free Length, in (mm) ................. 1.098 (27.9)
Exhaust Valve Spring Free Length, in (mm) ................. 1.098 (27.9)
Intake Valve Seat Width, in (mm) ................. 0.028 (0.70)
Exhaust Valve Seat Width, in (mm) ................. 0.028 (0.70)
Camshaft Journal Outside Diameter, in (mm) ................. 0.470-0.471 (11.953-11.968)

Tightening Torque Specs

Connecting Rod Bolt, Nm (ft-lb) ................. 9-11 (6.5-8.0)
Cylinder Head Bolt, Nm (ft-lb) ................. 20-24 (14.5-17.4)
Flywheel Nut, Nm (ft-lb) ................. 80-90 (57.9-65.1)
Carburetor Mounting Bolt, Nm (ft-lb) ................. 10-12 (7.2-8.7)
Starter Pulley, Nm (ft-lb) ................. 8-12 (5.8-8.7)
Fuel Cock Bolt, Nm (ft-lb) ................. 10-12 (7.2-8.7)
Muffler Mounting Nut, Nm (ft-lb) ................. 8-12 (5.8-8.7)
Fuel Tank Bolt, Nm (ft-lb) ................. 10-12 (7.2-8.7)
Spark Plug, Nm (ft-lbs) ................. 20 (14.7)

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