The Honda GX670U is a 670 cc, (41.0 cu·in) natural aspirated V-twin four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Honda Motor Company for general-purpose applications.
A 77.0 mm (3.03 in) cylinder bore and 72.0 mm (2.83 in) piston stroke give the GX670U engine a total of 670 cc of displacement. The compression ratio rating is 8.3:1.
The Honda GX670 U/R engine produced 20.8 PS (15.3 kW; 20.5 HP) at 3,600 rpm of maximum output power and 46.0 N·m (4.7 kg·m, 33.9 ft·lb) at 2,500 rpm of peak torque.
The Honda GX670U features:
- Overhead valve (OHV) design
- Transistorized magneto ignition system
- Horizontal type carburetor with butterfly valve
- Centrifugal governor
- Forced lubrication system
- Forced air cooling system
- Electric starter
General information
| Engine Specifications | |
| Engine model | GX670 U/R |
| Engine type | 4-stroke, OHV, V-twin |
| Displacement | 670 cm3, (40.89 cu·in) |
| Max. horsepower | 20.8 PS (15.3 kW; 20.5 HP) at 3,600 rpm |
| Max. torque | 46.0 N·m (4.7 kg·m, 33.9 ft·lb) at 2,500 rpm |
| Cooling system | Forced air |
| Air cleaner | Dual-element type |
| Lubricating system | Forced lubrication |
| Ignition system | Transistorized magneto ignition |
| Fuel system | Horizontal type carburetor with butterfly valve |
| Fuel consumption | 7.4L (1.96 US gal, 1.63 Imp gal)/hr |
| Fuel tank capacity | – |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Starting system | Electric starter |
| Stoping system | Ignition primary circuit ground |
| Governor | Centrifugal governor |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
| Dimensions (L x W X H) | – |
| Dry weight | 43.5 kg (95.9 lbs) |
Cylinder Block and Head
| Cylinder block | |
| Compression ratio: | 8.3:1 |
| Cylinder bore: | 77.0 mm (3.03 in) |
| Piston stroke: | 72.0 mm (2.83 in) |
| Cylinder internal diameter (standard): | 77.000 mm (3.0315 in) |
| Piston skirt outer diameter (standard): | 76.985 mm (3.0309 in) |
| Number of piston rings (compression / oil): | 2/1 |
| Crankshaft center distance: | 36 mm (1.415 in) |
| Cylinder head | |
| Valve arrangement: | OHV, gear driven |
| Valves: | 2,(4 valves in total) |
Tightening torque specs
| Tightening torque specs | |
| Connecting rod bolt | 12 Nm; 1.2 kg·m; 9 ft·lb |
| Cylinder head bolt | 34 Nm; 3.5 kg·m; 25 ft·lb |
| Socket bolt | 27 Nm; 2.7 kg·m; 20 ft·lb |
| Flywheel nut | 196 Nm; 20.0 kg·m; 145 ft·lb |
| Pivot bolt | 24 Nm; 2.4 kg·m; 17 ft·lb |
| Pivot adjusting nut | 10 Nm; 1.0 kg·m; 7 ft·lb |
| Cylinder head cover bolt | 9 Nm; 0.9 kg·m; 6.5 ft·lb |
| Oil level switch joint nut | 10 Nm; 1.0 kg·m; 7 ft·lb |
| Oil drain bolt | 39 Nm; 4.0 kg·m; 29 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) | 22 Nm; 2.2 kg·m; 16 ft·lb |
| Bolt, nut (10 mm) | 34 Nm; 3.5 kg·m; 25 ft·lb |
| Bolt, nut (12 mm) | 54 Nm; 5.5 kg·m; 40 ft·lb |
Service Data
| Engine | |
| Maximum speed: | 3,850±150 rpm rpm |
| Idle speed: | 1,450±150 rpm rpm |
| Cylinder compression: | 6.0-8.0 kg/cm2 (85-114 psi) at 500 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 lubrication |
| Oil type: | Honda 4-stroke or an equivalent (SJ or later) |
| Recommended oil: | SAE 10W-30 |
| Oil capacity: | With oil filter replacement:: 1.4 L (1.48 US. qt, 1.23 Imp. qt.) Without oil filter replacement:: 1.1 L (1.16 US. qt, 0.97 Imp. qt.) |
| Fuel system | |
| Type: | Horizontal type carburetor with butterfly valve |
| Ignition system | |
| Type: | Transistorized magneto ignition |
| Spark plug: | NGK ZGR5A DENSO J16CR-U |
| Spark plug gap: | 0.7-0.8 mm (0.0276-0.0315 in) |
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