Honda G100

Honda G100 2.0 HPThe Honda G100 is a 76 cc (4.6 cu.in.) 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
Model G100
Type 4-stroke, side valve type (L-head), single cylinder
Displacement 76 cm 3 (4.6 cu-in)
Max. horsepower 2.0 HP (1.5 kW) or 2.2 HP (1.6 kW) at 4200 rpm
Max. torque 3.3 Nm (0.33 kg·m, 2.4 ft·lb) or 3.5 Nm (0.35 kg·m, 2.5 ft·lb)
Carburetor Horizontal, butterfly valve
Cooling system Forced-air
Ignition system Flywheel magneto
Lubricating system Splash system
Starting system Recoil starter
Stoping system Ground of primary circuit
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity 1.4 L
Fuel consumption 320 g/HPh
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio: 6.5:1
Bore x Stroke 46 x 46 mm (1.81 in x 1.81 in in)
Sleeve internal diameter 46.00 mm (1.811 in)
Piston skirt outer diameter 45.980 mm (1.810 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top 0.025-0.055 mm (0.0009-0.0022 in)
Second/oil 0.010-0.040 mm (0.0004-0.0016 in)
Ring end gap Top/second 0.15-0.35 mm (0.006-0.014 in)
Oil 0.15-0.35 mm (0.006-0.014 in)
Connecting rod small end ID 10.0 mm (0.393 in)
Connecting rod big end ID 18.0 mm (0.708 in)
Crankpin outer diameter 17.973 mm (0.7076 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: Side valve type (L-head)
Valves: 2
Stem outer diameter (standard): INTAKE 5.490 mm (0.2161 in)
EXHAUST 5.445 mm (0.2143 in)
Guide internal diameter INTAKE / EXHAUST 5.5 mm (0.2165 in)
Spring free length 27.1 mm (1.066 in)
Cam height: INTAKE 18.10-18.40 mm (0.713-0.724 in)
EXHAUST 18.10-18.40 mm (0.713-0.724 in)

Maintenance data

Engine
Idle speed 1400 ± 110 rpm
Cylinder compression 6.5 kg/cm2 (637 kPa) at 800 rpm
Adjust timing ignition
Ignition timing 20° B.T.D.C. (Fixed)
Adjust valve clearance
Intake valve 0.08-0.16 mm (0.0031-0.0063 in)
Exhaust valve 0.08-0.16 mm (0.0031-0.0063 in)
Oil system
Oil type Honda 4-stroke “SE”
Recommended oil 10W-40
Oil capacity 0.45 L
Carburetor
Main jet #55
Pilot screw 1-3/8
Float height 6.7-9.7 mm (0.26-0.28 in)
Ignition system
Spark plug NGK: BM4A, BMR4A
NIPPON DENSO: W14M-U, W14MR-U
Spark plug gap 0.6-0.7 mm (0.024-0.028 in)
Primary winding ignition coil resistance 0.49 Ω±10%
Secondary winding ignition coil resistance 4.0 kΩ±10%

Tightening torque specs

Tightening torque specs
Carburetor 4-6 Nm; 0.4-0.6 kg·m; 2.9-4.3 ft·lb
Flywheel 45-55 Nm; 4.5-5.5 kg·m; 32.5-40 ft·lb
Governor arm 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Cylinder head 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Crankcase cover 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Connecting rod 4-6 Nm; 0.4-0.6 kg·m; 2.9-4.3 ft·lb
Others
5 mm bolts, nuts 4-7 Nm; 0.4-0.7 kg·m; 2.9-5.1 ft·lb
6 mm bolts, nuts 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
8 mm bolts, nuts 20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb
10 mm bolts, nuts 35-40 Nm; 3.5-4.0 kg·m; 25-29 ft·lb
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