The Honda GX390 RT2/T2/UT2 is a 0.4 L (389 cc, 23.74 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Honda Motor Company for general-purpose applications.
An 88.0 mm (3.46 in) cylinder bore and 64.0 mm (2.52 in) piston stroke give the GX390 RT2/T2/UT2 engine a total of 389 cc of displacement. The compression ratio rating is 8.2:1.
The Honda GX390 RT2/T2/UT2 engine produced 11.8 PS (8.7 kW; 11.7 HP) at 3,600 rpm of net power and or 9.5 PS (7.0 kW; 9.4 HP) at 3,600 rpm of continuous rated power and 26.5 N·m (2.7 kg·m, 19.5 ft·lb) at 2,500 rpm of peak torque.
The Honda GX390 RT2/T2/UT2 features:
- Overhead valve (OHV) design
- C.D.I.(Capacitor Discharge Ignition) type magneto ignition system
- Horizontal type carburetor with butterfly valve
- Centrifugal governor
- Forced splash lubrication system
- Forced air cooling system
- Recoil or recoil and starter motor
General information
| Engine Specifications | |
| Engine model | GX390 RT2/T2/UT2 |
| Engine type | 4-stroke, OHV, single-cylinder |
| Displacement | 389 cm3, (23.74 cu·in) |
| Max. horsepower | 11.8 PS (8.7 kW; 11.7 HP) at 3,600 rpm |
| Max. torque | 26.5 N·m (2.7 kg·m, 19.5 ft·lb) at 2,500 rpm |
| Cooling system | Forced air |
| Air cleaner | Dual element type, Cyclone type, Low profile type |
| Lubricating system | Forced splash |
| Ignition system | C.D.I.(Capacitor Discharge Ignition) type magneto ignition |
| Fuel system | Horizontal type carburetor with butterfly valve |
| Fuel consumption | 3.5 Liters (0.92 US gal, 0.77 Imp gal)/h |
| Fuel tank capacity | 6.1 L (1.61 US. gal. 1.34 Imp. gal.) |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Starting system | Recoil or recoil and starter motor |
| Stoping system | Ignition primary circuit open |
| Governor | Centrifugal governor |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Dimensions (L x W X H) | 407 x 485 x 449 mm (16 x 19.1 x 17.7 in) |
| Dry weight | 31.5 kg (69.4 lbs) |
Cylinder Block and Head
| Cylinder block | |
| Compression ratio: | 8.2:1 |
| Cylinder bore: | 88.0 mm (3.46 in) |
| Piston stroke: | 64.0 mm (2.52 in) |
| Cylinder internal diameter (standard): | 88.000-88.017 mm (3.4646-3.4652 in) |
| Piston skirt outer diameter (standard): | 87.975-87.985 mm (3.4636-3.464 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Connecting rod big end diameter (standard): | 36.025-36.039 mm (1.4183-1.4189 in) |
| Connecting rod small end diameter (standard): | 20.005-20.020 mm (0.7876-0.7882 in) |
| Piston pin diameter: | 19.994-20.000 mm (0.7872-0.7874 in) |
| Side clearance (Top): | 0.015-0.060 mm (0.0006-0.0024 in) |
| Side clearance (Second): | 0.030-0.060 mm (0.0012-0.0024 in) |
| Ring end gap (Top): | 0.200-0.350 mm (0.0079-0.0138 in) |
| Ring end gap (Second): | 0.350-0.500 mm (0.0138-0.0197 in) |
| Ring end gap (Oil): | 0.200-0.700 mm (0.0079-0.0276 in) |
| Ring width (Top): | 1.160-1.190 mm (0.0457-0.0469 in) |
| Ring width (Second): | 1.160-1.175 mm (0.0457-0.0463 in) |
| Crankpin journal diameter: | 35.975-35.985 mm (1.4163-1.4167 in) |
| Crankshaft center distance: | 32 mm (1.26 in) |
| Cylinder head | |
| Valve arrangement: | OHV, gear driven |
| Valves: | 2 |
| Valve steam diameter (INTAKE): | 6.575-6.590 mm (0.2589-0.2594 in) |
| Valve steam diameter (EXHAUST): | 6.535-6.550 mm (0.2573-0.2579 in) |
| Valve spring free length (INTAKE): | 39.0 mm (1.5354 in) |
| Valve spring free length (EXHAUST): | 39.0 mm (1.5354 in) |
| Camshaft lobe height (INTAKE): | 32.498-32.698 mm (1.2794-1.2873 in) |
| Camshaft lobe height (EXHAUST): | 31.985-32.185 mm (1.2592-1.2671 in) |
| Camshaft journal diameter : | 15.966-15.984 mm (0.6286-0.6293 in) |
Tightening torque
| Tightening torque specs | |
| Connecting rod bolt (M8x1.25 Special) | 14 Nm; 1.4 kg·m; 10 ft·lb |
| Cylinder head bolt (M10x1.25) | 35 Nm; 3.5 kg·m; 25 ft·lb |
| Flywheel nut (M16x1.5 Special) | 115 Nm; 11.5 kg·m; 83 ft·lb |
| Rocker arm pivot lock nut (M6x0.5) | 10 Nm; 1.0 kg·m; 7 ft·lb |
| Rocker arm pivot bolt (M8x1.25 Special) | 24 Nm; 2.4 kg·m; 17 ft·lb |
| Crankcase cover bolt (M8x1.25) | 24 Nm; 2.4 kg·m; 17 ft·lb |
| Oil level switch joint nut (M10x1.25) | 10 Nm; 1.0 kg·m; 7 ft·lb |
| Fuel filter joint nut (M10x1.25) | 2 Nm; 0.2 kg·m; 1.4 ft·lb |
| Muffler mounting nut (M8x1.25) | 24 Nm; 2.4 kg·m; 17 ft·lb |
| Air cleaner wing nut (M6x1.0) | 9 Nm; 0.9 kg·m; 6.5 ft·lb |
| Oil drain bolt (M12x1.5) | 23 Nm; 2.3 kg·m; 17 ft·lb |
| Fuel tank bolt (M8x1.25) | 24 Nm; 2.4 kg·m; 17 ft·lb |
| Air cleaner mounting nut (M6x1.0) | 10 Nm; 1.0 kg·m; 7 ft·lb |
| Fuel strainer cup (M24x1.0) | 4 Nm; 0.4 kg·m; 2.9 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 Data
| Engine | |
| Maximum speed: | 3,700-4,000 rpm |
| Idle speed: | 1,250-1,550 rpm |
| Cylinder compression: | 0.51-0.69 MPa (5.2-7.0 kgf/cm2, 74-100 psi) / 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 | |
| Lubrication system: | Forced splash |
| Oil type: | Honda 4-stroke or an equivalent (SE or later) |
| Recommended oil: | SAE 10W-30 |
| Oil capacity: | 1.1 L (1.16 US. qt, 0.97 Imp. qt.) |
| Fuel system | |
| Type: | Horizontal type carburetor with butterfly valve |
| Main jet | BE85C B: #100 BE85L A: #95 BE85Q A: #92 BE85Q A: #102 BE89F B: #108 BE89R A: #102 BE89U A: #108 BE94B A: #100 BE94A A: #115 |
| Float height | 13.2 mm (0.52 in) |
| Pilot screw opening | BE85C B: 1 – 3/4 turns out BE85L A: 2 turns out BE85Q A: 1 – 7/8 turns out BE85Q A: 2 – 1/4 turns out BE89F B: 2 – 1/4 turns out BE89R A: 2 – 1/4 turns out BE89U A: 2 – 1/4 turns out BE94B A: 1 – 3/4 turns out BE94A A: 2 – 1/4 turns out |
| Ignition system | |
| Type: | C.D.I.(Capacitor Discharge Ignition) type magneto ignition |
| Ignition timing: | B.T.D.C. 10° / 1,400 rpm |
| Spark plug: | NGK: BPR6ES DENSO: W20EPR-U |
| Spark plug gap: | 0.7-0.8 mm (0.0276-0.0315 in) |
| Spark plug torque: | 18 N·m (1.8 kg·m, 13.3 ft·lb) |
| Ignition coil air gap | 0.2-0.6 mm (0.0079-0.0236 in) |
Applications
| Manufacturer or Brand | Models |
| Generators | |
| Honda | EB5000X, EB6500X |
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