Honda G100

Honda G100 2.0 HPThe Honda G100 is a 76 cc (4.6 4-stroke, single-cylinder, air-coolled internal combustion small gasoline engine manufactured by Honda Motor Company since 1980.

The Honda G100 engine has a slide valve (L-head) design and camshaft driven by a single row chain driven by the crankshaft. The engine has a recoil starter, horizontal carburetor with butterfly valve and flywheel magneto or CDI ignition system.

The G100 engine a compression ratio rating is 6.5:1, cylinder bore and piston stroke are 46.0 mm (1.81 in) and 46.0 mm (1.81 in), respectively.

The Honda G100 produced 2.0 HP (1.5 kW) or 2.2 HP (1.6 kW) at 4200 rpm of maximum horsepower and 3.3 Nm (0.33 kg·m, 2.4 ft·lb) or 3.5 Nm (0.35 kg·m, 2.5 ft·lb) of maximum torque, depending on the engine application.

There are three versions of G100 engine:

  • Honda G100, with 76 cc of displacement and 2.0 HP or 2.2 HP of horsepower
  • Honda G100 K1, with 83 cc of displacement and 2.2 HP
  • Honda G100 K2, with 98 cc of displacement and 2.5 HP of maximum output power

General information

Engine Specifications
Type4-stroke, side valve type (L-head), single cylinder
Displacement76 cm 3 (4.6 cu-in)
Max. horsepower2.0 HP (1.5 kW) or 2.2 HP (1.6 kW) at 4200 rpm
Max. torque3.3 Nm (0.33 kg·m, 2.4 ft·lb) or 3.5 Nm (0.35 kg·m, 2.5 ft·lb)
CarburetorHorizontal, butterfly valve
Cooling systemForced-air
Ignition systemFlywheel magneto
Lubricating systemSplash system
Starting systemRecoil starter
Stoping systemGround of primary circuit
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity1.4 L
Fuel consumption320 g/HPh
PTO shaft rotationCounterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio:6.5:1
Bore x Stroke46 x 46 mm (1.81 in x 1.81 in in)
Sleeve internal diameter46.00 mm (1.811 in)
Piston skirt outer diameter45.980 mm (1.810 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop0.025-0.055 mm (0.0009-0.0022 in)
Second/oil0.010-0.040 mm (0.0004-0.0016 in)
Ring end gapTop/second0.15-0.35 mm (0.006-0.014 in)
Oil0.15-0.35 mm (0.006-0.014 in)
Connecting rod small end ID10.0 mm (0.393 in)
Connecting rod big end ID18.0 mm (0.708 in)
Crankpin outer diameter17.973 mm (0.7076 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:Side valve type (L-head)
Stem outer diameter (standard):INTAKE5.490 mm (0.2161 in)
EXHAUST5.445 mm (0.2143 in)
Guide internal diameterINTAKE / EXHAUST5.5 mm (0.2165 in)
Spring free length27.1 mm (1.066 in)
Cam height:INTAKE18.10-18.40 mm (0.713-0.724 in)
EXHAUST18.10-18.40 mm (0.713-0.724 in)

Maintenance data

Idle speed1400 ± 110 rpm
Cylinder compression6.5 kg/cm2 (637 kPa) at 800 rpm
Adjust timing ignition
Ignition timing20° B.T.D.C. (Fixed)
Adjust valve clearance
Intake valve0.08-0.16 mm (0.0031-0.0063 in)
Exhaust valve0.08-0.16 mm (0.0031-0.0063 in)
Oil system
Oil typeHonda 4-stroke “SE”
Recommended oil10W-40
Oil capacity0.45 L
Main jet#55
Pilot screw1-3/8
Float height6.7-9.7 mm (0.26-0.28 in)
Ignition system
Spark plug NGK: BM4A, BMR4A
Spark plug gap0.6-0.7 mm (0.024-0.028 in)
Primary winding ignition coil resistance0.49 Ω±10%
Secondary winding ignition coil resistance4.0 kΩ±10%

Tightening torque specs

Tightening torque specs
Carburetor4-6 Nm; 0.4-0.6 kg·m; 2.9-4.3 ft·lb
Flywheel45-55 Nm; 4.5-5.5 kg·m; 32.5-40 ft·lb
Governor arm8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Cylinder head8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Crankcase cover8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Connecting rod4-6 Nm; 0.4-0.6 kg·m; 2.9-4.3 ft·lb
5 mm bolts, nuts4-7 Nm; 0.4-0.7 kg·m; 2.9-5.1 ft·lb
6 mm bolts, nuts8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
8 mm bolts, nuts20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb
10 mm bolts, nuts35-40 Nm; 3.5-4.0 kg·m; 25-29 ft·lb
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