The Honda GX390 K1/T1/UT1 is a 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, such as construction equipment, tillers, generators, welders, pumps and other industrial applications.
The Honda GX390 K1 engine has a single cylinder inclined by 25°, overhead valve (OHV) design, horizontal type carburetor with butterfly valve, transistorized magneto ignition system, mechanical splash type lubricating system and forced-air cooling system. The GX390 K1 engine could be equipped with dual element type, oil-bath type or a cyclone-type air cleaner. The GX390K1 is equipped with 6.5 L (1.72 US. gal. 1.43 Imp. gal.) fuel tank.
The Honda GX390 K1 engine produced 13.6 PS (10.0 kW; 13.0 HP) at 3,600 rpm of maximum output power and 27.0 N·m (2.8 kg·m, 19.9 ft·lb) at 2,500 rpm of peak torque.
General information
| Engine Specifications | |
| Engine model | GX390 K1/T1/UT1 |
| Engine type | 4-stroke, OHV, single-cylinder |
| Displacement | 389 cm3, (23.74 cu·in) |
| Max. horsepower | 13.6 PS (10.0 kW; 13.0 HP) at 3,600 rpm |
| Max. torque | 27.0 N·m (2.8 kg·m, 19.9 ft·lb) at 2,500 rpm |
| Cooling system | Forced air |
| Air cleaner | Dual element type Oil-bath type Cyclone type |
| Lubricating system | Splash type |
| Ignition system | Transistorized magneto ignition |
| Fuel system | Horizontal type carburetor with butterfly valve |
| Fuel consumption | 313 g/kWh |
| Fuel tank capacity | 6.5 L (1.72 US. gal. 1.43 Imp. gal.) |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Starting system | Recoil or electric starter |
| Stoping system | Ignition primary circuit ground |
| Governor | Centrifugal govervor |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Dimensions (L x W X H) | 380 x 450 x 443 mm (15 x 17.7 x 17.4 in) |
| Dry weight | 31.0 kg (68.3 lbs) |
Cylinder Block and Head
The cylinder bore is 88.0 mm (3.46 in) and the piston stroke is 64.0 mm (2.52 in). Compression ratio rating is 8.0:1. The Honda GX390 K1 engine has a cast iron cylinder sleeve, ball bearing supported the crankshaft and heavy duty balancer shaft. The piston has two compression rings and a single oil ring.
| Cylinder block | |
| Compression ratio: | 8.0:1 |
| Cylinder bore: | 88.0 mm (3.46 in) |
| Piston stroke: | 64.0 mm (2.52 in) |
| Cylinder internal diameter (standard): | 88.000 mm (3.4646 in) |
| Piston skirt outer diameter (standard): | 87.985 mm (3.464 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Connecting rod big end diameter (standard): | 36.025 mm (1.4183 in) |
| Connecting rod small end diameter (standard): | 20.005 mm (0.7876 in) |
| Piston pin diameter: | 20.000 mm (0.7874 in) |
| Side clearance (Top): | 0.030-0.060 mm (0.0012-0.0024 in) |
| Side clearance (Second): | 0.030-0.060 mm (0.0012-0.0024 in) |
| Ring end gap (Top): | 0.20-0.40 mm (0.0079-0.0157 in) |
| Ring end gap (Second): | 0.20-0.40 mm (0.0079-0.0157 in) |
| Ring end gap (Oil): | 0.20-0.70 mm (0.0079-0.0276 in) |
| Ring width (Top): | 2.0 mm (0.0787 in) |
| Ring width (Second): | 2.0 mm (0.0787 in) |
| Crankpin journal diameter: | 35.985 mm (1.4167 in) |
| Crankshaft center distance: | 32 mm (1.26 in) |
| Cylinder head | |
| Valve arrangement: | OHV, gear driven |
| Valves:: | 2 |
| Valve steam diameter (INTAKE): | 6.59 mm (0.2594 in) |
| Valve steam diameter (EXHAUST): | 6.55 mm (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): | 32.40-32.80 mm (1.2756-1.2913 in) |
| Camshaft lobe height (EXHAUST): | 31.89-32.29 mm (1.2555-1.2713 in) |
| Camshaft journal diameter : | 15.984 mm (0.6293 in) |
Tightening torque
| Tightening torque settings | |
| Connecting rod bolt: | 14 Nm; 1.4 kg·m; 10 ft·lb; |
| Cylinder head bolt: | 35 Nm; 3.5 kg·m; 25 ft·lb; |
| Flywheel nut: | 115 Nm; 11.5 kg·m; 83 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; |
| Oil drain bolt: | 23 Nm; 2.3 kg·m; 17 ft·lb |
Service Data
The Honda 4-stroke or an equivalent (SE or later) oil with a viscosity of SAE 10W-30 is recommended for the GX390 K1, refilling oil capacity is 1.1 L (1.16 US. qt, 0.97 Imp. qt.). Recommended spark plug is NGK: BP6ES, BPR6ES; DENSO: W20EP-U, W20EPR-U with 0.7-0.8 mm (0.0276-0.0315 in) spark plug gap.
The valve clearance is 0.13-0.17 mm (0.0051-0.0067 in) for intake valves and 0.18-0.22 mm (0.0071-0.0087 in) for exhaust valves. Standard cylinder compression is 6.0-8.5 kg/cm2 (85-151 psi) at 600 rpm.
| Engine | |
| Maximum speed: | 3,850±150 rpm |
| Idle speed: | 1,400 ±150 rpm rpm |
| Cylinder compression: | 6.0-8.5 kg/cm2 (85-151 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 | |
| Lubrication system: | Splash type |
| 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: | Externally vented: #105 Internally vented: #115 |
| Float height: | 13.2 mm (0.5197 in) |
| Pilot screw opening: | Externally vented: 2-1/4 turns out Internally vented: 2-1/4 turns out |
| Ignition system | |
| Type: | Transistorized magneto ignition |
| Ignition timing: | B.T.D.C. 25° (Fixed) |
| Spark plug: | NGK: BP6ES, BPR6ES DENSO: W20EP-U, W20EPR-U |
| Spark plug gap: | 0.7-0.8 mm (0.0276-0.0315 in) |
| Ignition coil air gap | 0.2-0.4 mm (0.008-0.016 in) |
Applications
| Manufacturer or Brand | Models |
| Generators | |
| Honda | EB6500, EB6500X, EB6500SX, EB7000i, EC5000, EC6000, ECT6500, ECT7000, ECT7000P |
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