Honda GXR120 T/RT

Honda GXR120 T/RTThe Honda GXR120 T/RT is a 121 cc, (7.4 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.

Cylinder bore and piston stroke are 60.0 mm (2.36 in) and 43.0 mm (1.69 in), respectively. Compression ratio rating is 8.5:1.

The Honda GXR120 T/RT engine produced 3.7 PS (2.7 kW; 3.6 HP) at 3,600 rpm of maximum output power and 7.5 N·m (0.8 kg·m, 5.5 ft·lb) at 2,500 rpm of peak torque.

The Honda GXR120 T/RT features:

  • OHC design
  • Transistorized magneto ignition system
  • Float type, Horizontal butterfly valve type or Diaphragm type
  • Centrifugal governor
  • Splash lubrication system
  • Forced air cooling system
  • Recoil starter

General information

Engine Specifications
Engine model GXR120 T/RT
Engine type 4-stroke, OHC, single-cylinder
Displacement 121 cm3, (7.38 cu·in)
Max. horsepower 3.7 PS (2.7 kW; 3.6 HP) at 3,600 rpm
Max. torque 7.5 N·m (0.8 kg·m, 5.5 ft·lb) at 2,500 rpm
Cooling system Forced air
Air cleaner GXR120T: Single type, Dual type
GXR120RT: Single type, Dual type, Elbow type
Lubricating system Splash
Ignition system Transistorized magneto ignition
Fuel system Float type, Horizontal butterfly valve type or Diaphragm type
Fuel consumption 1.0 L (0.26 US gal, 0.22 Imp gal)/h
Fuel tank capacity
Fuel used Unleaded gasoline (octane number 86 or higher)
Starting system Recoil starter
Stoping system Ignition primary circuit ground
Governor Mechanical centrifuga
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio: 8.5:1
Cylinder bore: 60.0 mm (2.36 in)
Piston stroke: 43.0 mm (1.69 in)
Cylinder internal diameter (standard): 60.000-60.015 mm (2.3622-2.3628 in)
Piston skirt outer diameter (standard): 59.971-59.985 mm (2.3611-2.3616 in)
Number of piston rings (compression / oil): 2/1
Connecting rod big end diameter (standard): 26.020-26.033 mm (1.0244-1.0249 in)
Connecting rod small end diameter (standard): 13.005-13.020 mm (0.512-0.5126 in)
Piston pin diameter: 12.994-13.000 mm (0.5116-0.5118 in)
Side clearance (Top): 0.015-0.054 mm (0.0006-0.0021 in)
Side clearance (Second): 0.030-0.069 mm (0.0012-0.0027 in)
Ring end gap (Top): 0.150-0.300 mm (0.0059-0.0118 in)
Ring end gap (Second): 0.400-0.550 mm (0.0157-0.0217 in)
Ring end gap (Oil): 0.200-0.700 mm (0.0079-0.0276 in)
Ring width (Top): 0.970-0.990 mm (0.0382-0.039 in)
Ring width (Second): 1.155-1.175 mm (0.0455-0.0463 in)
Crankpin journal diameter: 25.970-25.980 mm (1.0224-1.0228 in)
Crankshaft center distance: 21.5 mm (0.845 in)
Cylinder head
Valve arrangement: OHC, 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): 25.8 mm (1.0157 in)
Valve spring free length (EXHAUST): 25.8 mm (1.0157 in)
Camshaft lobe height (INTAKE): 36.483 mm (1.4363 in)
Camshaft lobe height (EXHAUST): 36.483 mm (1.4363 in)

Service Data

Engine
Maximum speed: 4,100 ± 100 rpm
Idle speed: 1,850 ± 150 rpm
Cylinder compression: 5.1 kg/cm2 (73 psi) at 700 rpm
Valve clearance
Intake valve clearance (COLD): 0.13-0.17 mm (0.0051-0.0067 in)
Exhaust valve clearance (COLD): 0.18-0.22 mm (0.0071-0.0087 in)
Oil system
Lubrication system: Splash
Oil type: Honda 4-stroke or an equivalent (SE or higher)
Recommended oil: SAE 10W-30
Oil capacity: 0.28 L (0.3 US. qt, 0.25 Imp. qt.)
Fuel system
Type: Float type, Horizontal butterfly valve type or Diaphragm type
Main jet: Float type
BF33S A: #60
BF33R A: #60
Floatless type
#48
Float height: 15.7 mm (0.6181 in)
Pilot screw opening: Float type
BF33S A: 3-1/2 turns out
BF33R A: 3-3/8 turns out
Floatless type
2-3/4 turns out
Ignition system
Type: Transistorized magneto ignition
Ignition timing: 25° B.T.D.C.
Spark plug: NGK: CR5HSB
DENSO: U16FSR-UB
Spark plug gap: 0.7-0.8 mm (0.0276-0.0315 in)
Ignition coil air gap 0.5-0.7 mm (0.0197-0.0276 in)

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