Honda GX630

Honda GX630 engineThe Honda GX630 is a 688 cc (41.97 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 pressure washers, commercial lawn and garden equipment, tillers and cultivators, generators, forestry equipment, construction and industrial equipment, agricultural equipment, small vehicles, water pumps.

The Honda GX630 engine has an OHV (overhead valve) design with 90° V-twin cylinders; horizontal type, two-barrel inner-vent carburetor with butterfly valve; digital C.D.I.(Capacitor Discharge Ignition) ignition system with variable timing and electric starter.

The GX630 motor uses a hemispherical combustion chamber design. It offers a higher 9.3:1 compression ratio, higher power output and greater displacement in a more compact design. The cylinder bore is 78.0 mm (3.07 in) and the piston stroke is 72.0 mm (2.83 in). The GX630 engine produces 21.1 PS (15.5 kW; 20.8 HP) of maximum horsepower at 3,600 rpm; 16.3 PS (12.0 kW; 16.0 HP) of continuous rated power at 3,600 rpm., and 48.3 N·m (4.93 kg·m, 35.6 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Model GX630 / GX630R
Type 4-stroke, OHV, 90° V-twin
Displacement 688 cm 3 (41.97 cu-in)
Max. horsepower 21.1 PS (15.5 kW; 20.8 HP) at 3,600 rpm
Max. torque (crank PTO) 48.3 N·m (4.93 kg·m, 35.6 ft·lb) at 2,500 rpm
Carburetor Horizontal type, two barrel, inner-vent, butterfly valve
Cooling system Forced-air
Ignition system Digital C.D.I. with variable timing
Lubricating system Forced feed
Starting system Electric starter
Stoping system Ignition primary circuit open
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel consumption 6.0 L (1.59 US gal, 1.32 Imp gal) / h
PTO shaft rotation Counterclockwise (from PTO shaft side)

Dimensions and Weight

Length, mm (in) 405 (15.9)
Width, mm (in) 410 (16.1)
Height, mm (in) 438 (17.2)
Dry weight, kg (lb) 44.0 (96.8)

Cylinder Block and Head

The Honda GX630 engine uses integrated cylinder and head, a hemispherical combustion chamber, aluminum push rods with steel tips, racing inspired forged steel connecting rods and forged steel crankshaft with pressure fed crankshaft bearings,

Cylinder block
Compression ratio: 9.3:1
Bore x Stroke 78 X 72 mm (3.07 x 2.83 in)
Sleeve internal diameter 78.000-78.015 mm (3.0709-3.0715 in)
Piston skirt outer diameter 77.985-77.995 mm (3.0703-3.0707 in)
Ring side clearance Top/Second 0.050-0.080 mm (0.0020-0.0031 in)
Ring end gap Top/Second 0.20-0.35 mm (0.008-0.0138 in)
Oil (side rail 0.20-0.70 mm (0.008-0.028 in)
Ring width Top/Second 1.140-1.155 mm (0.0449-0.0455 in)
Connecting rod small end ID 18.006-18.018 mm (0.7089-0.7094 in)
Piston pin outer diameter 17.994-18.000 mm (0.7084-0.7087 in)
Crankpin diameter 44.973-44.983 mm (1.7706-1.7710 in)
Crankshaft journal diameter 39.984-40.000 mm (1.5742-1.5748 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 4 (2 per cylinder)
Stem outer diameter (standard): INTAKE 5.475-5.490 mm (0.2156-0.2161 in)
EXHAUST 5.435-5.450 mm (0.2140-0.2146 in)
Valve spring free length: 38.3 mm (1.51 in)
Valve lifter internal diameter: 6.010-6.040 mm (0.2366-0.2378 in)
Valve lifter shaft outer diameter: 5.970-6.000 mm (0.2350-0.2362 in)
Camshaft journal diameter: 16.982-17.000 mm (0.6686-0.6693 in)
Cam height: INTAKE 29.506-29.706 mm (1.1617-1.1695 in)
EXHAUST 29.410-29.610 mm (1.1579-1.1657 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt 22 Nm; 2.2 kg·m; 16 ft·lb
Cylinder nut 37 Nm; 3.8 kg·m; 27 ft·lb
Oil drain plug bolt 45 Nm; 4.5 kg·m; 33 ft·lb
Flywheel nut 235 Nm; 24.0 kg·m; 173 ft·lb
Oil filter cartridge 12 Nm; 1.2 kg·m; 9 ft·lb
Tappet adjusting nut 7.5 Nm; 0.75 kg·m; 5.5 ft·lb
Governor arm nut 11 Nm; 1.1 kg·m; 8 ft·lb
Fuel pump cover screw 4 Nm; 0.4 kg·m; 3 ft·lb
Oil pressure switch 9 Nm; 0.9 kg·m; 6.6 ft·lb

Service Information

Maximum speed 3,850 ± 150 rpm
Idle speed 1,400 ± 150 rpm
Cylinder compression 5.0-7.0 kg/cm2 (73-102 psi) at 500 rpm
Valve clearance
Intake valve clearance 0.08±0.02 mm
Exhaust valve clearance 0.10±0.02 mm
Oil system
Oil type Honda 4-stroke or an equivalent (SE or later)
Recommended oil SAE 10W-30
Oil capacity Without oil filter: 1.5 L (1.59 US qt, 1.32 Imp qt)
With oil filter: 1.7 L (1.80 US qt, 1.50 Imp qt)
Oil change interval Every 6 month or 100 Hrs.
Main jet Cylinder №1: #102
Cylinder №2: #105
Float height 15.5 mm (0.61 in)
Pilot screw opening Cylinder №1: 2 turns out
Cylinder №2: 1-7/8 turns out
Ignition system
Ignition timing 9°-23° B.T.D.C.
Spark plug NGK: ZFR5F
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
Ignition coil air gap 0.4 ± 0.2 (0.016 ± 0.008)
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  1. Hi, I have a honda GX630 generator in our ice cream van. It does a great job providing all the power we need, which is a lot. But very noisy. Do you know the decibels it runs at?. Also the actual output as it would appear to be more than what I assume is 630 kva. Thanks

  2. Garbage engine prone to failure. Engine failed after 1 year and 80 hours. Honda 3 waranty simply blames you and the gas saying the carb caused the failure causing a valve to seize up. Ill never buy honda again after the hell I went through dealing with them.

    • The motors “brand new” are usually shipped/delivered without oil in them. Did you fill it with oil before starting it? A seized valve is indicative of not enough/no oil in most/all gasoline engines.

  3. engine is used on a round bale wrapper to power a hydraulic pump I have 432 hours of use on it changed oil regularly it idles fine and when it revs back up to wrap a bale it smokes severely and consumes quit a bit of oil when in use, seems to have consistent power is there anything in the intake system that would cause excessive oil to be sucked into the intake to cause the smoke I am ready to tear the motor apart rehone the cylinders cylinders andput new rings in it it should not smoke like a dragon

  4. Anyone figure out how to get it to rev higher? (not the governor) the coils have a built in rev limiter.

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