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
ModelGX620 K1
Type4-stroke, OHV, 90° V-twin
Displacement614 cm 3 (37.5 cu-in)
Max. horsepower20 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
CarburetorHorizontal type, butterfly valve
Cooling systemForced-air
Ignition systemTransistorized magneto ignition
Lubricating systemForced lubrication
Starting systemRecoil starter or Recoil and electric starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel consumption230 g/HPh
PTO shaft rotationCounterclockwise (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 Stroke77 X 66 mm (3.0 x 2.6 in)
Sleeve internal diameter77.00 mm (3.03 in)
Piston skirt outer diameter76.985 mm (3.03 in)
Ring side clearanceTop/Second0.030-0.060 mm (0.0006-0.0018 in)
Ring end gapTop/Second0.20-0.40 mm (0.010-0.020 in)
Ring widthTop/Second1.990 mm (0.0783 in)
Connecting rod small end ID18.005 mm (0.7087 in)
Piston pin outer diameter18.000 mm (0.7087 in)
Crankpin diameter39.995 mm (1.5746 in)
Crankshaft journal diameter38.000 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):INTAKE6.590 mm (0.2594 in)
EXHAUST6.550 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:INTAKE29.865 mm (1.1758 in)
EXHAUST29.865 mm (1.1758 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt12 Nm; 1.2 kg·m; 9 ft·lb
Cylinder head bolt34 Nm; 3.5 kg·m; 25 ft·lb
Socket bolt27 Nm; 2.7 kg·m; 20 ft·lb
Flywheel nut196 Nm; 20.0 kg·m; 145 ft·lb
Pivot bolt24 Nm; 2.4 kg·m; 17 ft·lb
Pivot adjusting nut10 Nm; 1.0 kg·m; 7 ft·lb
Cylinder head cover bolt9 Nm; 0.9 kg·m; 6.5 ft·lb
Oil level switch joint nut10 Nm; 1.0 kg·m; 7 ft·lb
Oil drain bolt39 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 speed3,850 ± 100 rpm
Idle speed1,400 ± 150 rpm
Cylinder compression6.0-8.0 kg/cm2 (85-114 psi) at 500 rpm
Valve clearance
Intake valve clearance0.15±0.02 mm (0.006±0.001 in)
Exhaust valve clearance0.20±0.02 mm (0.008±0.001 in)
Oil system
Oil typeHonda 4-stroke or an equivalent (SG or SF)
Recommended oilSAE 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 intervalEvery 6 month or 100 Hrs.
Main jet#105
Float height14.0 mm (0.55 in)
Pilot screw opening1-3/4 turns out
Ignition system
Ignition timing20° B.T.D.C.
Spark plugNGK: ZGR5A
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance0.8-1.0 Ω
Secondary ignition coil resistance5.9-7.1 kΩ
Ignition coil air gap0.4 ± 0.2 (0.016 ± 0.008)
Starter motor
Brush length10.0 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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