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
Type4-stroke, OHC, single cylinder
Displacement98 cm 3 (6.0 cu-in)
Max. horsepower3.0 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
CarburetorHorizontal type, butterfly valve
Cooling systemForced-air
Ignition systemTransistorized magneto ignition
Lubricating systemSplash
Starting systemRecoil starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity1.2 L (0.32 US Gal, 0.26 Imp Gal.)
Fuel consumption240 g/PSh
PTO shaft rotationCounterclockwise (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 Stroke56 X 40 mm (2.2 x 1.6 in)
Sleeve internal diameter56.00 mm (2.2047 in)
Piston skirt outer diameter55.965-55.985 mm (2.2033-2.2041 in)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop0.015-0.050 mm (0.0006-0.0020 in)
Second/oil0.015-0.050 mm (0.0006-0.0020 in)
Ring end gapTop0.15-0.30 mm (0.006-0.012 in)
Second0.30-0.45 mm (0.012-0.018 in)
Connecting rod small end ID13.005-13.020 mm (0.5120-0.5126 in)
Crankshaft crank pin outer diameter23.970-23.980 mm (0.9437-0.9441 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHC
Stem outer diameter (standard):INTAKE3.970-3.985 mm (0.1563-0.1569 in)
EXHAUST3.935-3.950 mm (0.1549-0.1555 in)
Cam height:INTAKE36.483 mm (1.4363 in)
EXHAUST36.483 mm (1.4363 in)
Valve spring free length:25.8 mm (1.02 in)

Tightening torque specs

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 Information

Maximum speed4000 ± 200 rpm
Idle speed1550 ± 150 rpm
Cylinder compression5.0 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
Oil typeHonda 4-stroke or an equivalent (SE or SF)
Recommended oilSAE 10W-30
Oil capacity0.4 L (0.42 US. qt, 0.35 Imp. qt.)
Main jet#60
Pilot jet#35
Float height12 mm (0.47 in)
Pilot screw opening2-3/8 turns out
Ignition system
Spark plugNGK: CR5HSB
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
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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