Honda GX31

Honda GX31 engineThe Honda GX31 is a 31 cc (1.9 cu-in) single-cylinder, air-cooled, four-stroke cycle, internal combustion ultra-small gasoline motor manufactured by Honda Motor Company since 1997. In 2002 the GX31 engine were replaced with the Honda GX25.

This engine is a suitable power source for handheld applications like brush-cutters and non-handheld applications like concrete screeds, tillers, and pumps.

The Honda GX35 engine has an OHV design with valve rocker arms and camshaft driven by a maintenance-free, low-noise timing belt, makes the engine more compact and light.

It has a recoil starter, diaphragm type carburetor, and transistorized magneto ignition. Bore is 39.0 mm (1.5 in) and stroke is 26.0 mm (1.0 in). The GX31 produced 1.52 PS (1.5 HP, 1.12 kW) at 7,000 rpm and 1.64 Nm (0.17 kg·m; 1.21 lbf·ft) at 6,500 rpm.

General information

Engine Specifications
Type4-stroke, OHV, single-cylinder
Displacement31 cm 3 (1.9 cu-in)
Max. horsepower1.52 PS (1.5 HP, 1.12 kW) at 7,000 rpm
Max. torque1.64 Nm (0.17 kg·m; 1.21 lbf·ft) at 6,500 rpm
CarburetorDiaphragm type
Cooling systemForced-air
Ignition systemTransistorized magneto ignition
Lubricating systemPumping spray
Starting systemRecoil starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity0.65 liters (0.69 US.qts, 0.57 Imp. qts)
Fuel consumption340 g/kWh (250 g/HPh, 0.55 lb/HPh)
PTO shaft rotationCounterclockwise (from PTO shaft side)

Dimensions and Weight

Length, mm (in)210 (8.3)
Width, mm (in)251 (9.9)
Height, mm (in)250 (9.84)
Dry weight, kg (lb)3.4 (7.5)

Cylinder Block and Head

Cylinder block
Compression ratio:8.0:1
Bore x Stroke39.0 X 26.0 mm (1.5 x 1.0 in)
Sleeve internal diameter39.00 mm (1.535 in)
Piston skirt outer diameter38.99 mm (1.535 in)
Piston ring end gap (Top):0.10-0.25 mm (0.004-0.010 in)
Piston ring end gap (Second):0.10-0.25 mm (0.004-0.010 in)
Ring width (Top):0.98 mm (0.039 in)
Ring width (Second):0.98 mm (0.039 in)
Piston ring end gap (Oil):0.015-0.050 mm (0.006-0.0020 in)
Cylinder Head
Warpage (max)0.2 mm (0.01 in)
Valve Arrangement:OHV
Valve stem outer diameter (INTAKE):3.985 mm (0.1569 in)
Valve stem outer diameter (EXHAUST):3.950 mm (0.1555 in)
Valve guide outer diameter4.000 mm (0.1575 in)
Camshaft cam height (INTAKE):22.79 mm (0.897 in)
Camshaft cam height (EXHAUST):22.79 mm (0.897 in)
Camshaft outer diameter:5.020 mm (0.1976 in)

Maintenance data

Idle speed3,100 ± 200 rpm
Cylinder compression2.9-5.9 kg/cm2 (0.3-0.6 MPa, 41-84 psi) at 1,200 rpm
Valve clearance
Intake valve0.12 ± 0.02 (0.005 ± 0.001)
Exhaust valve0.15 ± 0.02 (0.006 ± 0.001)
Main jet#40
Oil system
Oil typeHonda 4-stroke or an equivalent (SG, SF)
Recommended oilSAE 10W-30
Oil capacity0.10 liters (0.11 US.qts, 0.09 Imp. qts)
Ignition system
Ignition timing27 ° B.T.D.C (Fixed)
Spark plugNGK: C5HSB, CR5HSB
Spark plug gap0.6-0.7 mm (0.024-0.028 in)
Primary ignition coil resistance0.7-0.9 Ω
Secondary ignition coil resistance3.6-5.5 kΩ
Ignition coil air gap0.35-0.50 mm (0.014-0.020 in)

Tightening torque specs

Tightening torque specs
Flywheel nut (M8)15 Nm; 1.5 kg·m; 11 ft·lb
Crankcase bolt (M5 5×55 mm)7 Nm; 0.75 kg·m; 5.1 ft·lb
Crankcase bolt (M5 5×18 mm)5 Nm; 0.55 kg·m; 3.6 ft·lb
Camshaft cover bolt (M4)3 Nm; 0.35 kg·m; 2.2 ft·lb
Recoil starter pulley (M8)8 Nm; 0.8 kg·m; 5.8 ft·lb
Clutch bolt (M8)15 Nm; 1.55 kg·m; 11 ft·lb
Cylinder head cover bolt (M5)4 Nm; 0.4 kg·m; 2.9 ft·lb
Standard torque values
Bolt, nut (5 mm)5.5 Nm; 0.55 kg·m; 4.0 ft·lb
Screw (3 mm)1 Nm; 0.1 kg·m; 0.7 ft·lb
Screw (6 mm)9 Nm; 0.9 kg·m; 6.5 ft·lb
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.

ATTENTION! Dear visitors, this site is not a trading platform, an official dealer or a spare parts supplier, so we do not have any price lists or spare parts catalogs. We are an information portal and provide the technical specifications of gasoline and diesel engines.

We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.


  1. Looking for a small engine GX31, Could you help me with that. That is going on a Concrete creed.

  2. I LIVE IN SLIDELL,. LA. I would like to buy a Carbreator form my GX-31 Tiller.
    Do you have a local address?

  3. I have a GX31,I bought It in year 2004.I have Been using it since now and it is very good and perfect. It is the best. From Brasil…

  4. I repair Honda products. The GX-31 is far superior to the GX-25. The GX-31 was certainly more expensive to manufacture. It is crucial to keep the oil level full and changed frequently. The Walbro Carburetor will need the Metering and fuel pump diaphram replaced for not start or poor running conditions. I have 2 Tillers with the engine myself.

Leave a Reply

Your email address will not be published.