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 |
We try to use official documentation and verify the published data, but errors may occur. In addition, specifications of machinery and equipment may vary depending on markets and modifications. We do not recommend the use of this data for spare parts or repairs. Use official service manuals or parts catalogs for your product.
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