Honda G400

Honda G400 engineThe Honda G400 is a 406 cc, (24.8 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.

This engine produced 10.1 PS (7.4 kW; 10.0 HP) at 3,600 rpm of horsepower and 23 N·m (2.3 kg·m, 17 ft·lb) of torque for crankshaft PTO type and 44 N·m (4.5 kg·m, 32.5 ft·lb) for camshaft PTO type engine. It has an 86.0 mm (3.39 in) cylinder bore and 70.0 mm (2.76 in) piston stroke. The compression ratio rating is 6.5:1 for the G400 engine or 6.8:1 for the G400K1 engine.

The Honda G400 features:

  • Sidevalve (L-head) design
  • Flywheel magneto or CDI ignition system
  • Horizontal carburetor with butterfly valve
  • Centrifugal govervor
  • Splash type lubrication system
  • Forced air cooling system
  • Recoil starter

General information

Engine Specifications
Engine modelG400
Engine type4-stroke, L-head, single-cylinder
Displacement406 cm3, (24.8 cu·in)
Max. horsepower10.1 PS (7.4 kW; 10.0 HP) at 3,600 rpm
Max. torque Crankshaft PTO: 23 N·m (2.3 kg·m, 17 ft·lb)
Camshaft PTO: 44 N·m (4.5 kg·m, 32.5 ft·lb)
Cooling systemForced air
Air cleanerSemi-dry, dry or oil-bath type
Lubricating systemSplash type
Ignition systemFlywheel magneto ignition or CDI ignition
Fuel systemHorizontal carburetor with butterfly valve
Fuel consumption370 g/kWh
Fuel tank capacity6.0 L (1.59 US. gal. 1.32 Imp. gal.)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemRecoil starter
Stoping systemIgnition primary circuit ground
GovernorCentrifugal govervor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)390 x 430 x 500 mm (15.4 x 16.9 x 19.7 in)

Cylinder Block and Head

Cylinder block
Compression ratio:6.5:1 or 6.8:1 (K1)
Cylinder bore:86.0 mm (3.39 in)
Piston stroke:70.0 mm (2.76 in)
Cylinder internal diameter (standard):86.000-86.020 mm (3.3858-3.3866 in)
Piston skirt outer diameter (standard):85.970-86.000 mm (3.3846-3.3858 in)
Number of piston rings (compression / oil):2/1
Connecting rod small end diameter (standard):19.005-19.020 mm (0.7482-0.7488 in)
Piston pin diameter:19.000 mm (0.748 in)
Side clearance (Top):0.020-0.060 mm (0.0008-0.0024 in)
Side clearance (Second):0.010-0.050 mm (0.0004-0.002 in)
Side clearance (Oil):0.010-0.050 mm (0.0004-0.002 in)
Ring end gap (Top):0.200-0.400 mm (0.0079-0.0157 in)
Ring end gap (Second):0.200-0.400 mm (0.0079-0.0157 in)
Ring end gap (Oil):0.200-0.400 mm (0.0079-0.0157 in)
Ring width (Top):1.970-1.990 mm (0.0776-0.0783 in)
Ring width (Second):1.970-1.990 mm (0.0776-0.0783 in)
Ring width (Oil):3.970-3.990 mm (0.1563-0.1571 in)
Crankpin journal diameter:36.943-36.959 mm (1.4544-1.4551 in)
Crankshaft center distance:35.0 mm (1.38 in)
Cylinder head
Valve arrangement:L-head
Valve steam diameter (INTAKE):6.955-6.970 mm (0.2738-0.2744 in)
Valve steam diameter (EXHAUST):6.910-6.925 mm (0.272-0.2726 in)
Valve spring free length (INTAKE):42.7 mm (1.6811 in)
Valve spring free length (EXHAUST):42.7 mm (1.6811 in)
Camshaft lobe height (INTAKE):38.46-38.72 mm (1.5142-1.5244 in)
Camshaft lobe height (EXHAUST):38.49-38.75 mm (1.5154-1.5256 in)

Tightening torque specs

Tightening torque specs
Fuel valve (12 mm)12-15 Nm; 1.2-1.5 kg·m; 8.7-10.8 ft·lb
Flywheel (16 mm)110-120 Nm; 11.0-12.0 kg·m; 80-87 ft·lb
Cylinder head Serial № before 129741: 43-47 Nm; 4.3-4.7 kg·m; 31-34 ft·lb
Serial № after 129742: 32-38 Nm; 3.2-3.8 kg·m; 23-27 ft·lb
Tappet cover (6 mm)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Crankcase cover (8 mm)20-24 Nm; 2.0-2.4 kg·m; 15-17 ft·lb
Connecting rod Serial № before 1085859: 21.6-26.4 Nm; 2.16-2.64 kg·m; 16-19 ft·lb
Serial № after 1085860: 24-28 Nm; 2.4-2.8 kg·m; 17-20 ft·lb
Fuel tank (8 mm)20-28 Nm; 2.0-2.8 kg·m; 15-20 ft·lb
Oil drain plug15-25 Nm; 1.5-2.5 kg·m; 11-18 ft·lb
5 mm bolts, nuts4-7 Nm; 0.4-0.7 kg·m; 2.9-5.1 ft·lb
6 mm bolts, nuts8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
8 mm bolts, nuts20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb
10 mm bolts, nuts35-40 Nm; 3.5-4.0 kg·m; 25-29 ft·lb

Service Data

The Honda 4-stroke “SE” oil with a viscosity of SAE 10W-40 is recommended for the G400, refilling oil capacity is 1.2 L (1.27 US. qt, 1.06 Imp. qt.). Recommended spark plug is NGK: B4H, BR4HS for the magneto ignition system, and NGK: BP4HS-10, BPR4HS-10 for CDI ignition system.

The valve clearance is 0.08-0.16 mm (0.0031-0.0063 in) for intake valves and 0.11-0.19 mm (0.0043-0.0075 in) for exhaust valves. Standard cylinder compression is 5.3 kg/cm2 (75 PSI) at 800 rpm.

Idle speed:1,400&plsmn;150 rpm rpm
Cylinder compression:5.3 kg/cm2 (75 PSI) at 800 rpm
Valve clearance
Intake valve clearance:0.08-0.16 mm (0.0031-0.0063 in)
Exhaust valve clearance:0.11-0.19 mm (0.0043-0.0075 in)
Oil system
Lubrication system:Splash type
Oil type:SAE 10W-40
Recommended oil:Honda 4-stroke “SE”
Oil capacity:1.2 L (1.27 US. qt, 1.06 Imp. qt.)
Fuel system
Type:Horizontal carburetor with butterfly valve
Main jet:#102
Float height:8.6 mm (0.3386 in)
Pilot screw opening:2 turns out
Ignition system
Type:Flywheel magneto ignition or CDI ignition
Ignition timing: 20° B.T.D.C. – for magneto ignition
The CDI type does not require adjustment.
Spark plug:NGK: B4H, BR4HS for magneto ignition
NGK: BP4HS-10, BPR4HS-10 for CDI ignition
Spark plug gap: 0.6-0.7 mm (0.024-0.028 in), for magneto ignition system
0.9-0.10 mm (0.035-0.039 in), for CDI ignition system


Manufacturer or BrandModels
HondaE3500, E4500, EB3800, EB4000, EMS4000, EMS4500, ES4500, ET4500
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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