Honda GX120T1

Honda GX120T1The Honda GX120 T1 is a 118 cc (7.2 cu-in) single-cylinder inclined by 25° air-cooled 4-stroke internal combustion small gasoline engine manufactured by Honda Motor Company for general-purpose applications, such as commercial lawn and garden equipment, tillers and cultivators, generators, construction and industrial equipment, agricultural equipment and water pumps.

The Honda GX120 T1 engine has an OHV (overhead valve) design; high compression ratio for better fuel efficiency; horizontal type carburetor with butterfly valve; heavy-duty recoil or electric starter and transistorized magneto ignition system.

The cylinder bore is 60.0 mm (2.4 in) and the piston stroke is 42.0 mm (1.7 in), compression ratio rating is 7.5:1 or 8.5:1. The engine produced 2.9 kW (4.0 HP) of horsepower at 4,000 rpm.

Maximum torque:

  • Crank P.T.O.: 7.5 N·m (0.75 kg·m, 5.4 ft·lb) at 2,500 rpm.
  • With 1/2 reduction: 15 N·m (1.5 kg·m, 11 ft·lb) at 1,250 rpm.
  • With 1/6 reduction: 45 N·m (4.5 kg·m, 33 ft·lb) at 420 rpm.

General information

Engine Specifications
Model GX120 T1
Type 4-stroke, OHV, single cylinder inclined by 25°
Displacement 118 cm 3 (7.2 cu-in)
Max. horsepower 4.0 HP (2.9 kW) at 4,000 rpm
Max. torque (crank PTO) 7.5 N·m (0.75 kg·m, 5.4 ft·lb) at 2,500 rpm
Carburetor Horizontal type, butterfly valve
Cooling system Forced-air
Ignition system Transistorized magneto ignition
Lubricating system Splash
Starting system Recoil starter
Stoping system Ignition primary circuit ground
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel tank capacity 2.5 L (0.66 US Gal, 0.55 Imp Gal.)
Fuel consumption 230 g/PSh
PTO shaft rotation Counterclockwise (from PTO shaft side)

Cylinder Block and Head

The Honda GX120 has cast iron cylinder sleeve, ball bearing supported forged steel crankshaft, improved piston design. The piston has two compression rings and one oil ring. Precision camshaft design offers precise valve timing and optimal valve overlap for better fuel efficiency.

Cylinder block
Compression ratio: 7.5:1 or 8.5:1
Bore x Stroke 60 X 42 mm (2.4 x 1.7 in)
Sleeve internal diameter 60.00 mm (2.36 in)
Piston skirt outer diameter 59.985 mm (2.3616 in)
Number of piston rings (compression / oil): 2 / 1
Ring side clearance Top 0.015-0.045 mm (0.0006-0.0018 in)
Second/Oil 0.015-0.045 mm (0.0006-0.0018 in)
Ring end gap Top/Second 0.20-0.40 mm (0.008-0.016 in)
Oil 0.15-0.35 mm (0.006-0.014 in)
Ring width Top/Second 1.5 mm (0.06 in)
Oil 2.5 mm (0.10 in)
Connecting rod small end ID 13.005 mm (0.5120 in)
Connecting rod big end ID 26.02 mm (1.024 in)
Piston pin outer diameter 13.0 mm (0.51 in)
Crankshaft crank pin outer diameter 25.98 mm (1.023 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 2
Stem outer diameter (standard): INTAKE 5.48 mm (0.216 in)
EXHAUST 5.44 mm (0.214 in)
Valve spring free length: 30.5 mm (1.20 in)
Camshaft outer diameter: 13.984 mm (0.5506 in)
Cam height: INTAKE 27.7 mm (1.09 in)
EXHAUST 27.75 mm (1.093 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt 12 Nm; 1.2 kg·m; 9 ft·lb
Cylinder head bolt 24 Nm; 2.4 kg·m; 17 ft·lb
Flywheel nut 75 Nm; 7.5 kg·m; 54 ft·lb
Rocker arm pivot lock nut 10 Nm; 1.0 kg·m; 7 ft·lb
Rocker arm pivot bolt 24 Nm; 2.4 kg·m; 17 ft·lb
Crankcase cover bolt 12 Nm; 1.2 kg·m; 9 ft·lb
Oil level switch joint nut 10 Nm; 1.0 kg·m; 7 ft·lb
Oil drain bolt 18 Nm; 1.8 kg·m; 13 ft·lb
Standard torque values
Bolt, nut (5 mm) 5.5 Nm; 0.55 kg·m; 4.0 ft·lb
Bolt, nut (6 mm) 10 Nm; 1.0 kg·m; 7 ft·lb
Bolt, nut (8 mm) 24 Nm; 2.4 kg·m; 17 ft·lb
Bolt, nut (10 mm) 37.5 Nm; 3.75 kg·m; 27 ft·lb
Bolt, nut (12 mm) 55 Nm; 5.5 kg·m; 40 ft·lb

Service Information

Maximum speed 3,900 ± 100 rpm
Idle speed 1,400 ± 150 rpm
Cylinder compression 6.0-8.5 kg/cm2 (85-121 psi) at 600 rpm
Valve clearance
Intake valve clearance 0.15±0.02 mm (0.006±0.001 in)
Exhaust valve clearance 0.20±0.02 mm (0.008±0.001 in)
Oil system
Oil type Honda 4-stroke or an equivalent (SE or SF)
Recommended oil SAE 10W-30
Oil capacity 0.6 L (0.63 US. qt, 0.53 Imp. qt.)
Main jet Externally vented carburetor bowl: #60
Internally vented carburetor bowl: #62
Float height 13.7 mm (0.54 in)
Pilot screw opening Externally vented carburetor bowl: 2 turns out
Internally vented carburetor bowl: 2-3/8 turns out
Ignition system
Ignition timing 25° B.T.D.C. (Fixed)
Spark plug NGK: BP6ES, BPR6ES
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance 0.8-1.0 Ω
Secondary ignition coil resistance 5.9-7.1 kΩ
Ignition coil air gap 0.4 ± 0.2 (0.016 ± 0.008)
Starter motor
Brush length 11.0 mm (0.43 in)
Mica depth 1.6 mm (0.06 in)
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