Honda GX670

Honda GX670 engineThe Honda GX670 is a 670 cc (40.9 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 GX670 engine has an OHV (overhead valve) design with 90° V-twin cylinders; horizontal type carburetor with butterfly valve; 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 72.0 mm (2.8 in), the compression ratio rating is 8.3:1. The GX670 engine produced 24 HP (17.7 kW HP) of horsepower at 3,600 rpm and 50.8 N·m (5.18 kg·m, 37.5 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Model GX670
Type 4-stroke, OHV, 90° V-twin
Displacement 670 cm 3 (40.9 cu-in)
Max. horsepower 24 HP (17.7 kW HP) at 3,600 rpm
Max. torque (crank PTO) 50.8 N·m (5.18 kg·m, 37.5 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 Electric starter
Stoping system Ignition primary circuit ground
Fuel used Unleaded gasoline (octane number 86 or higher)
Fuel consumption 265 g/HPh
PTO shaft rotation Counterclockwise (from PTO shaft side)

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 GX670 U/R motor 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 72 mm (3.0 x 2.8 in)
Sleeve internal diameter 77.00 mm (3.03 in)
Piston skirt outer diameter 76.985 mm (3.03 in)
Cylinder Head
Warpage (limit) 0.10 mm (0.004 in)
Valve Arrangement: OHV
Valves: 4 (2 per cylinder)

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 1.90 L
Oil change interval Every 6 month or 100 Hrs.
Ignition system
Spark plug NGK: ZGR5A
Spark plug gap 0.7-0.8 mm (0.028-0.031 in)
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We try to use verified sources and official documentation, however, differences between sources or errors in entering information may occur. We do not provide advice on technical issues related to the engines operation or repair. We do not recommend using provided information for engines repairing engines or spare parts ordering, use only official service manuals and spare-parts catalogs.


    • Hello, we are not a supplier of engines, we are only an information portal with technical specifications, so we have no any price lists.

    • The Honda GX690 (22.1 hp) is about $1500, or so, but the exhaust is optional at about another $150. A Predator from Harbor Freight is a Honda clone and rated at 22 hp. Most parts will interchange. The Predator, presently, retails for $749. It’s a much better buy.

      • I personally dont think the predator is that great considering the fact that it is chinese and will only last a couple hundred hours or miles depending on use. Performance670 makes some great parts for them though.

  1. I have a gx670 v twin motor front coil fires good back one not at all bought a new coil still wont fire is there a difference in the front and back coil

  2. I’m trying to mount a mag pickup off the fly wheel. Is there another way to get a rpm reading for a external computer?

  3. Hej , jeg har en Honda Gx 670 generator, den går op og ned i omdrejninger, den starter fint, men vil ikke gå op og yde max, hvad kan det skyldes, mvh Lars Friis

  4. I just bought a duck boat with a gx670 with electric srart motor. The manual shows a fuel pump attached to the motor. But it has a external inline fuel pump. Dose this mean the original fuel pump is not working?

  5. A Predator 22 hp is the same engine but with a 1″ shaft. An adapter is available from Amazon It can be bought much cheaper than the Honda and the muffler is standard while it is an additional price on the Honda. It’s now called a GX670 (22.1 hp rated).

    • I have found that a small motorcycle battery would work for mine, as long as you have a charging system on your motor and it dosen’t take a lot of cranking to get your motor started.

  6. I have a GX690 that overfills with fuel after running and then won’t start (Hydrolics) the engine and forces fuel down through the piston rings into the oil. any Ideas??

  7. It’s possible that those who put everything together didn’t realize the motor had it’s own fuel pump. The external pump shouldn’t hurt anything.

  8. I have a GX 670 for sale on ebay if anyone is looking to buy.. it was a back up motor for a carpet cleaning machine. I only used it 2 days prob 8 hrs total use. I paid $1200 asking for $700 and u pay shippin. thanks! questions will be answerd on ebay guys take care.

  9. i have tried 3 carbs runs if i put gas manul and yes fuel pump works what is my problem

  10. I have a GX 670 motor on my small ride on loader
    It goes ok then when I unbalance it it Starts to put out heaps of white smoke
    Does any body know how the oil would get into the. Piston chamber
    Thank you

  11. Hi, I have a GX670 that smokes quite a bit blue/white burnt oil smoke especially with full throttle. So far I have tested compression both cylinders have 130 psi, new plugs, clean fuel, clean carb, no oil coming out of the breather hose, intake ports do not have oil, exhaust ports do not have oil (so the guides are not leaking), spark is good since the engine runs good BUT smokes. Changed oil and filter (not overfilled) for sure. Head gaskets are a suspect but with such awesome compression I am hesitant to pull it apart. Any suggestions would be much appreciated.

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