Honda GX670 U/R

Honda GX670 U/RThe 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:

  • 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 (COLD): 0.13-0.17 mm (0.0051-0.0067 in)
Exhaust valve clearance (COLD): 0.18-0.22 mm (0.0071-0.0087 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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