Honda GX620 U1/R1

Honda GX620 U1/R1The Honda GX620 U1/R1 is a 614 cc, (37.5 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.

Cylinder bore and piston stroke are 77.0 mm (3.03 in) and 66.0 mm (2.6 in), respectively. The compression ratio rating is 8.3:1.

The Honda GX620 U1/R1 engine produced 18.4 PS (13.5 kW; 18.1 HP) at 3,600 rpm of maximum output power and 40.6 N·m (4.1 kg·m, 29.9 ft·lb) at 2,500 rpm of peak torque.

The Honda GX620 U1/R1 features:

  • Overhead valve (OHV) design
  • Transistorized magneto ignition system
  • Horizontal type carburetor with butterfly valve
  • Centrifugal governor
  • Forced lubrication system
  • Forced air cooling system
  • Recoil or electric starter

General information

Engine Specifications
Engine model GX620 U1/R1
Engine type 4-stroke, OHV, V-twin
Displacement 614 cm3, (37.47 cu·in)
Max. horsepower 18.4 PS (13.5 kW; 18.0 HP) at 3,600 rpm
Max. torque 40.6 N·m (4.1 kg·m, 29.9 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 313 g/kWh
Fuel used Unleaded gasoline (octane number 86 or higher)
Starting system Recoil or 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) 388 x 457 x 452 mm (15.3 x 18 x 17.8 in)
Dry weight 42.0 kg (92.6 lbs)

Cylinder Block and Head

Cylinder block
Compression ratio: 8.3:1
Cylinder bore: 77.0 mm (3.03 in)
Piston stroke: 66.0 mm (2.6 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
Connecting rod small end diameter (standard): 18.005 mm (0.7089 in)
Piston pin diameter: 18.000 mm (0.7087 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 width (Top): 1.990 mm (0.0783 in)
Ring width (Second): 1.990 mm (0.0783 in)
Crankshaft main journal diameter: 38.000 mm (1.4961 in)
Crankpin journal diameter: 39.995 mm (1.5746 in)
Crankshaft center distance: 33.0 mm (1.3 in)
Cylinder head
Valve arrangement: OHV, gear driven
Valves: 2 ,(4 valves in total)
Valve steam diameter (INTAKE): 6.590 mm (0.2594 in)
Valve steam diameter (EXHAUST): 6.550 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): 29.865 mm (1.1758 in)
Camshaft lobe height (EXHAUST): 29.865 mm (1.1758 in)
Camshaft journal diameter : 16.985 mm (0.6687 in)

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
Idle speed: 1,400 ±150 rpm rpm
Cylinder compression: 6.0-8.0 kg/cm2 (85-121 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: Forced lubrication
Oil type: Honda 4-stroke or an equivalent (SG or SF)
Recommended oil: SAE 10W-30 or 10W-40
Oil capacity: 1.50 L (1.59 US. qt, 1.32 Imp. qt.)
Fuel system
Type: Horizontal type carburetor with butterfly valve
Ignition system
Type: Transistorized magneto ignition
Ignition timing: B.T.D.C. 20° (Fixed)
Spark plug: NGK: ZGR5A DENSO: J16CR-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)
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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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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