Honda GX100

Honda GX100The Honda GX100 is a 98 cc (5.98 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Honda Motor Company for general-purpose applications.

A 56.0 mm (2.2 in) cylinder bore and 40.0 mm (1.57 in) piston stroke give the GX100 engine a total of 98 cc of displacement. The compression ratio rating is 8.5:1.

The Honda GX100 engine produced 3.0 PS (2.2 kW; 3.0 HP) at 3,600 rpm of maximum output power and 5.7 N·m (0.6 kg·m, 4.2 ft·lb) at 3,600 rpm of peak torque.

The Honda GX100 features:

  • Overhaed camshaft OHC design
  • Transistorized magneto ignition system
  • Horizontal type carburetor with butterfly valve
  • Centrifugal governor
  • Splash lubrication system
  • Forced air cooling system
  • Recoil starter

General information

Engine Specifications
Engine modelGX100
Engine type4-stroke, OHC, single-cylinder
Displacement98 cm3, (5.98 cu·in)
Max. horsepower3.0 PS (2.2 kW; 3.0 HP) at 3,600 rpm
Max. torque5.7 N·m (0.6 kg·m, 4.2 ft·lb) at 3,600 rpm
Cooling systemForced air
Air cleanerDual-element type
Lubricating systemSplash
Ignition systemTransistorized magneto ignition
Fuel systemHorizontal type carburetor with butterfly valve
Fuel consumption240 g/PSh
Fuel tank capacity1.2 L (0.32 US. gal. 0.26 Imp. gal.)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemRecoil starter
Stoping systemIgnition primary circuit ground
GovernorCentrifugal governor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)
Dry weight

Cylinder Block and Head

Cylinder block
Compression ratio:8.5:1
Cylinder bore:56.0 mm (2.2 in)
Piston stroke:40.0 mm (1.57 in)
Cylinder internal diameter (standard):56.000 mm (2.2047 in)
Piston skirt outer diameter (standard):55.965-55.985 mm (2.2033-2.2041 in)
Number of piston rings (compression / oil):2/1
Connecting rod small end diameter (standard):13.005-13.020 mm (0.512-0.5126 in)
Side clearance (Top):0.015-0.050 mm (0.0006-0.002 in)
Side clearance (Second):0.015-0.050 mm (0.0006-0.002 in)
Side clearance (Oil):0.015-0.050 mm (0.0006-0.002 in)
Ring end gap (Top):0.150-0.300 mm (0.0059-0.0118 in)
Ring end gap (Second):0.300-0.450 mm (0.0118-0.0177 in)
Crankpin journal diameter:23.970-23.980 mm (0.9437-0.9441 in)
Crankshaft center distance:20 mm (0.785 in)
Cylinder head
Valve arrangement:OHC
Valve steam diameter (INTAKE):3.970-3.985 mm (0.1563-0.1569 in)
Valve steam diameter (EXHAUST):3.935-3.950 mm (0.1549-0.1555 in)
Valve spring free length (INTAKE):25.800 mm (1.0157 in)
Valve spring free length (EXHAUST):25.800 mm (1.0157 in)
Camshaft lobe height (INTAKE):36.483 mm (1.4363 in)
Camshaft lobe height (EXHAUST):36.483 mm (1.4363 in)

Tightening torque

Tightening torque specs
Connecting rod bolt5 Nm; 0.5 kg·m; 3.6 ft·lb
Oil dran plug bolt18 Nm; 1.8 kg·m; 13 ft·lb
Valve adjusting lock nut7.5 Nm; 0.75 kg·m; 5.4 ft·lb
Flywheel nut42 Nm; 4.3 kg·m; 31 ft·lb
Governor arm nut10 Nm; 1.0 kg·m; 7 ft·lb
Stopper plate screw1 Nm; 0.1 kg·m; 0.7 ft·lb
Spark plug11.8 Nm; 1.2 kg·m; 8.7 ft·lb

Service Data

Maximum speed:4,000 ± 200 rpm
Idle speed:1,550 ± 150 rpm
Cylinder compression:5.0 kg/cm2 (71 psi) at 700 rpm
Valve clearance
Intake valve0.15 ± 0.04 mm (0.006 ± 0.002 in)
Exhaust valve0.20 ± 0.04 mm (0.008 ± 0.002 in)
Oil system
Lubrication system:Splash
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.)
Fuel system
Type:Horizontal type carburetor with butterfly valve
Main jet:#60
Float height:12 mm mm (0.4724 in)
Pilot screw opening:2-3/8 turns out
Ignition system
Type:Transistorized magneto ignition
Spark plug gap:0.7-0.8 mm (0.0276-0.0315 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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