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Engine Specifications |
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| Model | GX390K1 |
| Type | 4-stroke, OHV, single cylinder, inclined by 25° |
| Displacement | 389 cm 3 (23.7 cu·in) |
| Max. horsepower | 13.0 HP (10.0 kW) at 3,600 rpm |
| Max. torque (crank PTO) | 27 Nm (2.7 kg·m, 20.0 ft·lb) at 2,500 rpm |
| Carburetor | Horizontal type, butterfly valve |
| Cooling system | Forced-air |
| Ignition system | Transistorized magneto ignition |
| Lubricating system | Forced splash |
| Starting system | Recoil and Starter motor |
| Stoping system | Ignition primary circuit ground |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel consumption | 6.5 Liters (1.72 US gal, 1.43 Imp gal) / h |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Honda GX390K1 (Type S) | |
| Length, mm (in) | 380 (15.0) |
| Width, mm (in) | 450 (17.7) |
| Height, mm (in) | 443 (17.4) |
| Dry weight, kg (lb) | 31.0 (68.3) |
| Operating weight, kg (lb) |
37.0 (81.6) |
| Cylinder block | ||
| Compression ratio: | 8.0:1 | |
| Bore x Stroke | 88 X 64 mm (3.5 x 2.5 in) | |
| Sleeve internal diameter | 88.000 mm (3.465 in) | |
| Piston skirt outer diameter | 87.985 mm (3.4640 mm) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Ring side clearance | Top/second | 0.030 – 0.060 (0.0012 – 0.0024) |
| Ring end gap | Top | 0.20 – 0.40 mm (0.01 – 0.02 in) |
| Second | 0.20 – 0.40 mm (0.01 – 0.02 in) | |
| Oil (side rail) | 0.20 – 0.70 mm (0.01 – 0.03 in) | |
| Ring width | Top | 2.0 mm (0.08 in) |
| Second | 2.0 mm (0.08 in) | |
| Connecting rod small end I.D. | 20.005 mm (0.7876 in) | |
| Connecting rod big end I.D. | 36.025 mm (1.4183 in) | |
| Crankshaft outer diameter | 35.985 mm (1.4167 in) | |
| Cylinder Head | ||
| Warpage (limit) | 0.10 mm (0.004 in) | |
| Valve Arrangement: | OHV | |
| Valves: | 2 | |
| Stem outer diameter (standard): | INTAKE | 6.590 mm (0.2594 in) |
| EXHAUST | 6.550 mm (0.2579 in) | |
| Guide inner diameter: | INTAKE/EXHAUST | 6.60 mm (0.6260 in) |
| Cam height: | INTAKE | 32.40-32.80 mm (1.276-1.291 in) |
| EXHAUST | 31.89-32.29 mm (1.256-1.271 in) | |
| Camshaft outer diameter: | 15.984 mm (0.6293 in) | |
| 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 |
| Engine | |
| Maximum speed | 3850 ± 150 rpm |
| Idle speed | 1400 ± 150 rpm |
| Cylinder compression | 6.0-8.5 kg/cm2 (85-121 psi, 0.59 – 0.83 MPa) at 600 rpm |
| Valve clearance | |
| Intake valve | 0.15 ± 0.02 (0.006 ± 0.001) |
| Exhaust valve | 0.20 ± 0.02 (0.008 ± 0.001) |
| Carburetor | |
| Main jet | Externally vented carburetor bowl: #105 Internally vented carburetor bowl: #115 |
| Float height | 13.2 mm (0.52 in) |
| Pilot screw opening | Externally vented carburetor bowl: 2-1/2 Internally vented carburetor bowl: 3 |
| Oil system | |
| Oil type | Honda 4-stroke or an equivalent (SE or later) |
| Recommended oil | SAE 10W-30 |
| Oil capacity | 1.1 L (1.16 US gal, 0.97 lmp qt) |
| Ignition system | |
| 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 (0.028-0.031 in) |
| Air gap | 0.2-0.6 mm (0.01-0.02 in) |
| Starter motor | |
| Brush length | 7.0 mm (0.28 in) limit: 3.5 mm (0.14 in) |
| Mica depth | 1.0 mm (0.04 in) limit: 0.2 (0.01) |
