Honda GX620K1

Honda GX620 K1 engineThe Honda GX620 is a 614 cc (37.5 cu-in) V-twin cylinder air-cooled four-stroke internal combustion small gasoline engine with horizontal shaft manufactured by Honda Motor Company for general-purpose applications, such as concrete saws, pressure washers, chipper and shredders, trenchers, generators, vibratory rollers, ride-on cement trowels, lawn tractors.

The Honda GX620 K1 engine has an OHV (overhead valve) design with 90° V-twin cylinders; horizontal type carburetor with butterfly valve; heavy-duty recoil and electric starter, or only electric starter and transistorized magneto ignition system.

The 90° V-twin OHV format featuring an advanced combustion chamber design and superior intake and exhaust efficiency combines the ordinarily opposed elements of good fuel economy and high power output at the highest possible levels. An advanced breather design and three-piece oil ring improve oil circulation efficiency for lower oil consumption. The result is excellent reliability plus reduced running and maintenance costs.

The cylinder bore is 77.0 mm (3.0 in) and the piston stroke is 66.0 mm (2.6 in), compression ratio rating is 8.3:1. The GX620K1 engine produced 20 HP (14.9 kW) of horsepower at 3,600 rpm and 44.1 N·m (4.50 kg·m, 32.5 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Model GX620 K1
Type 4-stroke, OHV, 90° V-twin
Displacement 614 cm 3 (37.5 cu-in)
Max. horsepower 20 HP (14.9 kW HP) at 3,600 rpm
Max. torque (crank PTO) 44.1 N·m (4.50 kg·m, 32.5 ft·lb) at 2,500 rpm
Carburetor Horizontal type, butterfly valve
Cooling system Forced-air
Ignition system Transistorized magneto ignition
Lubricating system Forced lubrication
Starting system Recoil starter or Recoil and electric starter
Stoping system Ignition primary circuit ground
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel consumption 230 g/HPh
PTO shaft rotation Counterclockwise (from PTO shaft side)

Dimensions and Weight

Length, mm (in) 388 (15.3) 408 (16.1) 379 (15.0)
Width, mm (in) 457 (18.0)
Height, mm (in) 452 (17.8)
Dry weight, kg (lb) 42.0 (92.6)
Operating weight, kg (lb) 43.0 (94.8)

Cylinder Block and Head

Improved crankcase rigidity, extra-durable crankshaft, and optimized cam shape reduce mechanical noise and contribute to quieter, smoother continuous operation. The Honda GX620K1 equipped with high-strength sintered aluminum connecting rods to reduce weight in overlap areas and minimize vibration caused by the cylinder offset.

Cylinder block
Compression ratio: 8.3:1
Bore x Stroke 77 X 66 mm (3.0 x 2.6 in)
Sleeve internal diameter 77.00 mm (3.03 in)
Piston skirt outer diameter 76.985 mm (3.03 in)
Ring side clearance Top/Second 0.030-0.060 mm (0.0006-0.0018 in)
Ring end gap Top/Second 0.20-0.40 mm (0.010-0.020 in)
Ring width Top/Second 1.990 mm (0.0783 in)
Connecting rod small end ID 18.005 mm (0.7087 in)
Piston pin outer diameter 18.000 mm (0.7087 in)
Crankpin diameter 39.995 mm (1.5746 in)
Crankshaft journal diameter 38.000 mm (1.4961 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 4 (2 per cylinder)
Stem outer diameter (standard): INTAKE 6.590 mm (0.2594 in)
EXHAUST 6.550 mm (0.2579 in)
Valve spring free length: 39.0 mm (1.54 in)
Valve lifter internal diameter: 6.010 mm (0.2366 in)
Valve lifter shaft outer diameter: 6.000 mm (0.2362 in)
Camshaft journal diameter: 16.985 mm (0.6687 in)
Cam height: INTAKE 29.865 mm (1.1758 in)
EXHAUST 29.865 mm (1.1758 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 Information

Maximum speed 3,850 ± 100 rpm
Idle speed 1,400 ± 150 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
Oil type Honda 4-stroke or an equivalent (SG or SF)
Recommended oil SAE 10W-30
Oil capacity With oil filter: 1.80 L (1.90 US. qt, 1.58 Imp. qt.)
Without oil filter: 1.50 L (1.59 US. qt, 1.32 Imp. qt.)
Oil change interval Every 6 month or 100 Hrs.
Main jet #105
Float height 14.0 mm (0.55 in)
Pilot screw opening 1-3/4 turns out
Ignition system
Ignition timing 20° B.T.D.C.
Spark plug NGK: ZGR5A
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance 0.8-1.0 Ω
Secondary ignition coil resistance 5.9-7.1 kΩ
Ignition coil air gap 0.4 ± 0.2 (0.016 ± 0.008)
Starter motor
Brush length 10.0 mm (0.43 in)
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  1. My dad left me this GX620 after he passed away. But my nephew and niece where trying to sell it behind my back and sold some of the parts . So now I’m trying to get it back to it’s original state before I got screwed over . Flywheel cover and air filter. So thanks for the info you could help me with

  2. I want to buy HONDA GX620 or GX630 or GX690 so can you kindly send me the Quotation and your banking details

  3. What do you suppose a fluctuating motor means? It almost sounds like it’s not getting enough fuel into it. Motor idles fine – just not fluid like it used to be? Old gas? (It’s a 10 year old motor. Can’t recall when the filter was changed, nor the spark plugs)

    • Hi Pat
      I have a similar problem with motor fluctuating
      fuel filter not blocked, oil level ok, appears to run a bit better with the choke half on , fuel solanoid OK , carby is clean
      Thanks if you have any suggestions

      • Burnish out the main jet and idle jet passage. Use a gas welders cleaning set., the little skewed wires fit tight and make for a slightly larger orifice so that our lousy alcohol bearing fuel will run a bit richer in order for it to run right. The fuel leaves a plaque in the jets – causing it to lean out/run lousy. Put 4 oz of 2 cycle ashless oil and 2-3 oz marvel mystery oil in 5 gal fuel & mark the container for (4stroke air cooled engines)…”treated fuel” The alcohol in the fuel kills piston rings if treated fuel is not used. We used this stuff on the carriers at sea for our air cooled recip engines. Veteran

  4. I
    I want to buy HONDA GX620 or GX630 To replace my ld motor in my skid loader 1818 Case. So can you send me the Quotationfor these items

  5. I purchased a club car carryall (294) from a lady who got it from her dad’s will. Know nothing about it’s history. I put a new carb, fuel pump, sending unit (gas tank), plugs, changed oil&filter. Ran fine for awhile, now I am getting a goodly amount of gas in the oil
    where do I look for a fix?? bad intake valve, bad rings, or what! has 285 hours on the engine meter.

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