Honda GXH50

The Honda GXH50 is a 49 cc (2.99 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion gasoline engine with a horizontal shaft, manufactured by Honda Motor Company for general-purpose applications.

It has an 41.8 mm (1.65 in) cylinder bore and 36.0 mm (1.42 in) piston stroke. The compression ratio rating is 8.0:1.

The GXH50 engine produced 2.4 PS (1.8 kW; 2.4 HP) at 7,000 rpm of maximum horsepower and 3.04 N·m (0.3 kg·m, 2.2 ft·lb) at 4,500 rpm of maximum torque.

The Honda GXH50 features:

  • OHV design
  • Transistorized magneto ignition system
  • Float type carburetor
  • Centrifugal governor
  • Splash lubrication system
  • Forced air cooling system
  • Recoil starter

General information

Engine Specifications
Engine model GXH50
Engine type 4-stroke, OHV, single-cylinder
Displacement 49 cm3, (2.99 cu·in)
Max. horsepower 2.4 PS (1.8 kW; 2.4 HP) at 7,000 rpm
Max. torque 3.04 N·m (0.3 kg·m, 2.2 ft·lb) at 4,500 rpm
Cooling system Forced air
Air cleaner Semi-dry type
Lubricating system Splash
Ignition system Transistorized magneto ignition
Fuel system Float type carburetor
Fuel consumption 240 g/HPh
Fuel tank capacity 0.77 L (0.2 US. gal. 0.17 Imp. gal.)
1.2 L (0.32 US. gal, 0.26 Imp. gal.)
Starting system Recoil starter
Stoping system Ignition primary circuit ground
Governor Centrifugal governor
PTO shaft rotation Counterclockwise (from PTO shaft side)
Dimensions (L x W X H) 225 x 274 x 353 mm (8.9 x 10.8 x 13.9 in)
Dry weight 5.5 kg (12.1 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio: 8.0:1
Cylinder bore: 41.8 mm (1.65 in)
Piston stroke: 36.0 mm (1.42 in)
Cylinder internal diameter (standard): 41.800-41.815 mm (1.6457-1.6463 in)
Piston skirt outer diameter (standard): 41.770-41.790 mm (1.6445-1.6453 in)
Number of piston rings (compression / oil): 2/1
Connecting rod small end diameter (standard): 10.006-10.007 mm (0.3939-0.394 in)
Connecting rod center distance: 15.000-15.011 mm (0.5906-0.591 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)
Ring end gap (Top): 0.150-0.300 mm (0.0059-0.0118 in)
Ring end gap (Second): 0.150-0.300 mm (0.0059-0.0118 in)
Ring width (Top): 0.770-0.790 mm (0.0303-0.0311 in)
Ring width (Second): 0.970-0.990 mm (0.0382-0.039 in)
Crankpin journal diameter: 14.973-14.984 mm (0.5895-0.5899 in)
Cylinder head
Valve arrangement: OHV, gear driven
Valves: 2
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): 23.7 mm (0.9331 in)
Valve spring free length (EXHAUST): 23.7 mm (0.9331 in)
Camshaft lobe height (INTAKE): 27.972 mm (1.1013 in)
Camshaft lobe height (EXHAUST): 27.972 mm (1.1013 in)

Tightening torque specs

Tightening torque specs
Spark plug 12 Nm; 1.2 kg·m; 8.6 ft·lb
Connecting rod bolt 6 Nm; 0.6 kg·m; 4.3 ft·lb
Crankcase cover bolt 7.5 Nm; 0.75 kg·m; 5.4 ft·lb
Oil case bolt 7.5 Nm; 0.75 kg·m; 5.4 ft·lb
Flywheel nut 22 Nm; 2.2 kg·m; 16 ft·lb
Igniton coil bolt 6 Nm; 0.6 kg·m; 5 ft·lb
Carburetor drain screw 1.2 Nm; 0.12 kg·m; 0.9 ft·lb
Carburetor drain bolt 4.5 Nm; 0.45 kg·m; 3.3 ft·lb
Others
4 mm bolts, nuts 3.5 Nm; 0.35 kg·m; 2.5 ft·lb
5 mm bolts, nuts 5.5 Nm; 0.55 kg·m; 4.0 ft·lb
6 mm bolts, nuts 10 Nm; 1.0 kg·m; 7 ft·lb

Service Data

Engine
Maximum speed: 7,800 ± 150 rpm
Idle speed: 2,500 ± 20 rpm
Cylinder compression: 4.3 kg/cm2 (61 psi) at 1,000 rpm
Valve clearance
Intake valve clearance: 0.06-0.10 mm (0.0024-0.0039 in)
Exhaust valve clearance: 0.09-0.13 mm (0.0035-0.0051 in)
Oil system
Lubrication system: Splash
Oil type: Honda 4-stroke or an equivalent (SE or SF)
Recommended oil: SAE 10W-30
Oil capacity: 0.25 L (0.26 US. qt, 0.22 Imp. qt.)
Fuel system
Type: Float type carburetor
Main jet: #55
Float height: 12.0 mm (0.4724 in)
Pilot screw opening: 1-1/8 turns out
Ignition system
Type: Transistorized magneto ignition
Ignition timing: 30° B.T.D.C.
Spark plug: NGK: CR5HSB DENSO: U16FSR-UB
Spark plug gap: 0.6-0.7 mm (0.0236-0.0276 in)
Spark plug torque: 12 N·m (1.2 kg·m, 8.8 ft·lb)
Ignition coil air gap 0.3-0.5 mm (0.0118-0.0197 in)

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