Honda GX100

Honda GX100 engineThe Honda GX100 is a 98 cc (6.0 cu-in) single-cylinder air-cooled 4-stroke internal combustion small gasoline engine manufactured by Honda Motor Company for general-purpose applications, such as commercial lawn and garden equipment, construction and industrial equipment, agricultural equipment and water pumps.

This engine has an OHC design for increased efficiency and optimal power transfer; high compression ratio for better fuel efficiency; horizontal type carburetor with butterfly valve; sophisticated air intake system; large capacity, multi-chamber exhaust system, heavy-duty recoil starter and transistorized magneto ignition system.

A 56.0 mm (2.2 in) cylinder bore and 40.0 mm (1.60 in) piston stroke give the Honda GX100 engine a total of 98 cc of displacement. Compression ratio rating is 8.5:1. It produced 2.2 kW (3.0 PS) of horsepower at 3,600 rpm and 5.7 N·m (0.59 kg·m, 4.2 ft·lb) of torque at 3,600 rpm.

General information

Engine Specifications
Model GX100
Type 4-stroke, OHC, single cylinder
Displacement 98 cm 3 (6.0 cu-in)
Max. horsepower 3.0 PS (2.2 kW) at 3,600 rpm
Max. torque (crank PTO) 5.7 N·m (0.59 kg·m, 4.2 ft·lb) at 3,600 rpm
Carburetor Horizontal type, butterfly valve
Cooling system Forced-air
Ignition system Transistorized magneto ignition
Lubricating system Splash
Starting system Recoil starter
Stoping system Ignition primary circuit ground
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity 1.2 L (0.32 US Gal, 0.26 Imp Gal.)
Fuel consumption 240 g/PSh
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

The Honda GX100 has cast iron cylinder sleeve, ball bearing supported forged steel crankshaft, improved piston design. The piston has two compression rings and one oil ring. Precision camshaft design offers precise valve timing and optimal valve overlap for better fuel efficiency.

Cylinder block
Compression ratio: 8.5:1
Bore x Stroke 56 X 40 mm (2.2 x 1.6 in)
Sleeve internal diameter 56.00 mm (2.2047 in)
Piston skirt outer diameter 55.965-55.985 mm (2.2033-2.2041 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top 0.015-0.050 mm (0.0006-0.0020 in)
Second/oil 0.015-0.050 mm (0.0006-0.0020 in)
Ring end gap Top 0.15-0.30 mm (0.006-0.012 in)
Second 0.30-0.45 mm (0.012-0.018 in)
Connecting rod small end ID 13.005-13.020 mm (0.5120-0.5126 in)
Crankshaft crank pin outer diameter 23.970-23.980 mm (0.9437-0.9441 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHC
Valves: 2
Stem outer diameter (standard): INTAKE 3.970-3.985 mm (0.1563-0.1569 in)
EXHAUST 3.935-3.950 mm (0.1549-0.1555 in)
Cam height: INTAKE 36.483 mm (1.4363 in)
EXHAUST 36.483 mm (1.4363 in)
Valve spring free length: 25.8 mm (1.02 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt 5 Nm; 0.5 kg·m; 3.6 ft·lb
Oil dran plug bolt 18 Nm; 1.8 kg·m; 13 ft·lb
Valve adjusting lock nut 7.5 Nm; 0.75 kg·m; 5.4 ft·lb
Flywheel nut 42 Nm; 4.3 kg·m; 31 ft·lb
Governor arm nut 10 Nm; 1.0 kg·m; 7 ft·lb
Stopper plate screw 1 Nm; 0.1 kg·m; 0.7 ft·lb
Spark plug 11.8 Nm; 1.2 kg·m; 8.7 ft·lb

Service Information

Maximum speed 4000 ± 200 rpm
Idle speed 1550 ± 150 rpm
Cylinder compression 5.0 kg/cm2 (71 psi) at 700 rpm
Valve clearance
Intake valve 0.15 ± 0.04 mm (0.006 ± 0.002 in)
Exhaust valve 0.20 ± 0.04 mm (0.008 ± 0.002 in)
Oil system
Oil type Honda 4-stroke or an equivalent (SE or SF)
Recommended oil SAE 10W-30
Oil capacity 0.4 L (0.42 US. qt, 0.35 Imp. qt.)
Main jet #60
Pilot jet #35
Float height 12 mm (0.47 in)
Pilot screw opening 2-3/8 turns out
Ignition system
Spark plug NGK: CR5HSB
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
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