The Honda G400 is a 406 cc (24.8 cu.in.) single-cylinder, air-cooled, four0-stroke, internal combustion small gasoline engine manufactured by Honda Motor Company since 1978 for general-purpose applications.
The Honda G400 engine has a slide valve (L-head) design and camshaft driven by a single row chain driven by the crankshaft. The engine has an electric or recoil starter, horizontal carburetor with butterfly valve and transistorized magneto or contact point breaker (CDI) ignition system.
Cylinder bore and piston stroke are 86.0 mm (3.4 in) and 70.0 mm (2.8 in), respectively. Compression ratio is 6.5:1 for G400 and 6.8:1 for G400K1.
The Honda G400 produced 10.1 PS (7.45 KW; 10.0 HP) at 3,600 rpm of maximum horsepower and 22.5 Nm (2.3 kg·m; 16.61 lbf·ft) at 3,600 rpm of peak torque. The dry weight of the Honda G400 with electric starter engine was 33 kg (72.7 lbs.).
General information
| Engine Specifications | |
| Model | G400 |
| Type | 4-stroke, side valve type (L-head), single cylinder |
| Displacement | 406 cm 3 (24.8 cu-in) |
| Max. horsepower | 10.1 PS (7.45 KW; 10.0 HP) at 3,600 rpm |
| Max. torque | 22.5 Nm (2.3 kg·m; 16.61 lbf·ft) at 3,600 rpm |
| Carburetor | Horizontal, butterfly valve |
| Cooling system | Forced-air |
| Ignition system | Transistorized magneto or CDI |
| Lubricating system | Splash type |
| Starting system | Recoil or electric starter |
| Stoping system | Ground switch |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 6.0 liters (6.3 US.qts, 5.3 Imp. qts) |
| Fuel consumption | 270 g/HPh |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: |
G400 – 6.5:1 G400K1 – 6.8:1 |
|
| Bore x Stroke | 86 X 70 mm (3.4 x 2.8 in) | |
| Sleeve internal diameter | 86.00-86.02 mm (3.3858-3.3866 in) | |
| Piston skirt outer diameter | 85.97-86.00 mm (3.385-3.386 in) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Piston ring side clearance (Top): | 0.020-0.060 mm (0.0008-0.0024 in) | |
| Piston ring side clearance (Second): | 0.010-0.050 mm (0.0004-0.0020 in) | |
| Piston ring side clearance (Oil): | 0.010-0.050 mm (0.0004-0.0020 in) | |
| Piston ring end gap (Top): | 0.200-0.400 mm (0.008-0.016 in) | |
| Piston ring end gap (Second): | 0.200-0.400 mm (0.008-0.016 in) | |
| Piston ring end gap (Oil): | 0.200-0.400 mm (0.008-0.016 in) | |
| Ring width (Top): | 1.970-1.990 mm (0.0776-0.783 in) | |
| Ring width (Second): | 1.970-1.990 mm (0.0776-0.783 in) | |
| Ring width (Oil): | 3.970-3.990 mm (0.1563-0.1571 in) | |
| Connecting rod small end ID | 19.005-19.020 mm (0.7482-07488 in) | |
| Crankshaft crankpin outer diameter | 36.943-36.959 mm (1.4544-1.1551 in) | |
| Cylinder Head | ||
| Warpage (limit) | 0.10 mm (0.004 in) | |
| Valve Arrangement: | Side valve type | |
| Valves: | 2 | |
| Valve stem outer diameter (INTAKE): | 6.955-6.970 mm (0.2738-0.2744 in) | |
| Valve stem outer diameter (EXHAUST): | 6.910-6.925 mm (0.2720-0.2726 in) | |
| Valve guide inner diameter (INTAKE): | 7.000-7.015 mm (0.2756-0.2762 in) | |
| Valve guide inner diameter (EXHAUST): | 7.000-7.015 mm (0.2756-0.2762 in) | |
| Spring free length | 42.7 mm (1.6811 in) | |
| Camshaft cam height (INTAKE): | 38.460-38.720 mm (1.5142-1.5244 in) | |
| Camshaft cam height (EXHAUST): | 38.490-38.750 mm (1.5154-1.5256 in) | |
Maintenance data
| Engine | |
| Idle speed | 1,400 ± 150 rpm |
| Cylinder compression | 5.3 kg/cm2 (75 psi) |
| Adjust timing ignition | |
| Ignition timing |
20° B.T.D.C. – for magneto ignition The CDI type does not require adjustment. |
| Adjust valve clearance | |
| Intake valve | 0.05-0.11 ± 0.02 (0.0020-0.0043 in) |
| Exhaust valve | 0.09-0.15 ± 0.02 (0.0035-0.0059 in) |
| Oil system | |
| Oil type | Honda 4-stroke “SE” |
| Recommended oil | 10W-40 |
| Oil capacity | 1.2 liters (1.3 US.qts, 1.1 Imp. qts) |
| Carburetor | |
| Main jet | #102 |
| Float height | 8.6 mm (0.34 in) |
| Ignition system | |
| 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 0.9-0.10 mm (0.035-0.039 in), for CDI ignition |
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 plug | 15-25 Nm; 1.5-2.5 kg·m; 11-18 ft·lb |
| Others | |
| 5 mm bolts, nuts | 4-7 Nm; 0.4-0.7 kg·m; 2.9-5.1 ft·lb |
| 6 mm bolts, nuts | 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb |
| 8 mm bolts, nuts | 20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb |
| 10 mm bolts, nuts | 35-40 Nm; 3.5-4.0 kg·m; 25-29 ft·lb |
bestelnummer distributieketting voor motor G 400 motoculteur
i’m in need of an exciter coil for the g400 or g300 if anyone has some parts laying around. apparently this has been discontinued for some time.
Hello,
can you give me the spacing of the platinum screws for the Honda G400 engine SVP?
Can this engine really run on Unleaded?
I have one form the 80’s and was under the impression in required leadded fuel.
Cheers
From owners manual: “Use any automotive gasoline”, but in the manual, for the G100 (the same G-series) we can see: “Unleaded gasoline (or regular grade)”.
THERE IS A SPARE PART OF HONDA G400 HERE?
Maybe
Does the 10 horse Honda engine from a generator have a tapered or keyed shaft?
1 inch with a keyway.
Hi can I convert this engine to start electronicly and where can I get the kit and a video maybe to show me how it is done. Thanks Bill
i need a new carb for my g400, what carb can i replace with please?
What was the G400 normally used for? I’m just wondering if it would be possible to apply it to a generator? Any idea what this engine is most suitable for?
Yes, this engine was used for Honda generators, which ones you can see here https://www.wersis.net/honda/g400.html