The 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
| Engine | |
| 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.) |
| Carburetor | |
| 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 NIPPONDENSO: W20EP-U, W20EPR-U |
| 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) |
Author:
Very educated