Honda GX390 K1

Honda GX390 K1 engineThe Honda GX390 K1/T1/UT1 is a 389 cc, (23.74 cu·in) natural aspirated single-cylinder four-stroke air-cooled internal combustion small gasoline engine with a horizontal shaft, manufactured by Honda Motor Company for general-purpose applications, such as construction equipment, tillers, generators, welders, pumps and other industrial applications.

The Honda GX390 K1 engine has a single cylinder inclined by 25°, overhead valve (OHV) design, horizontal type carburetor with butterfly valve, transistorized magneto ignition system, mechanical splash type lubricating system and forced-air cooling system. The GX390 K1 engine could be equipped with dual element type, oil-bath type or a cyclone-type air cleaner. The GX390K1 is equipped with 6.5 L (1.72 US. gal. 1.43 Imp. gal.) fuel tank.

The Honda GX390 K1 engine produced 13.6 PS (10.0 kW; 13.0 HP) at 3,600 rpm of maximum output power and 27.0 N·m (2.8 kg·m, 19.9 ft·lb) at 2,500 rpm of peak torque.

General information

Engine Specifications
Engine modelGX390 K1/T1/UT1
Engine type4-stroke, OHV, single-cylinder
Displacement389 cm3, (23.74 cu·in)
Max. horsepower13.6 PS (10.0 kW; 13.0 HP) at 3,600 rpm
Max. torque27.0 N·m (2.8 kg·m, 19.9 ft·lb) at 2,500 rpm
Cooling systemForced air
Air cleaner Dual element type
Oil-bath type
Cyclone type
Lubricating systemSplash type
Ignition systemTransistorized magneto ignition
Fuel systemHorizontal type carburetor with butterfly valve
Fuel consumption313 g/kWh
Fuel tank capacity6.5 L (1.72 US. gal. 1.43 Imp. gal.)
Fuel usedUnleaded gasoline (octane number 86 or higher)
Starting systemRecoil or electric starter
Stoping systemIgnition primary circuit ground
GovernorCentrifugal govervor
PTO shaft rotationCounterclockwise (from PTO shaft side)
Dimensions (L x W X H)380 x 450 x 443 mm (15 x 17.7 x 17.4 in)
Dry weight31.0 kg (68.3 lbs)

Cylinder Block and Head

The cylinder bore is 88.0 mm (3.46 in) and the piston stroke is 64.0 mm (2.52 in). Compression ratio rating is 8.0:1. The Honda GX390 K1 engine has a cast iron cylinder sleeve, ball bearing supported the crankshaft and heavy duty balancer shaft. The piston has two compression rings and a single oil ring.

Cylinder block
Compression ratio:8.0:1
Cylinder bore:88.0 mm (3.46 in)
Piston stroke:64.0 mm (2.52 in)
Cylinder internal diameter (standard):88.000 mm (3.4646 in)
Piston skirt outer diameter (standard):87.985 mm (3.464 in)
Number of piston rings (compression / oil):2/1
Connecting rod big end diameter (standard):36.025 mm (1.4183 in)
Connecting rod small end diameter (standard):20.005 mm (0.7876 in)
Piston pin diameter:20.000 mm (0.7874 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 end gap (Oil):0.20-0.70 mm (0.0079-0.0276 in)
Ring width (Top):2.0 mm (0.0787 in)
Ring width (Second):2.0 mm (0.0787 in)
Crankpin journal diameter:35.985 mm (1.4167 in)
Crankshaft center distance:32 mm (1.26 in)
Cylinder head
Valve arrangement:OHV, gear driven
Valve steam diameter (INTAKE):6.59 mm (0.2594 in)
Valve steam diameter (EXHAUST):6.55 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):32.40-32.80 mm (1.2756-1.2913 in)
Camshaft lobe height (EXHAUST):31.89-32.29 mm (1.2555-1.2713 in)
Camshaft journal diameter :15.984 mm (0.6293 in)

Tightening torque

Tightening torque settings
Connecting rod bolt:14 Nm; 1.4 kg·m; 10 ft·lb;
Cylinder head bolt:35 Nm; 3.5 kg·m; 25 ft·lb;
Flywheel nut:115 Nm; 11.5 kg·m; 83 ft·lb;
Rocker arm pivot lock nut:10 Nm; 1.0 kg·m; 7 ft·lb;
Rocker arm pivot bolt:24 Nm; 2.4 kg·m; 17 ft·lb;
Oil drain bolt:23 Nm; 2.3 kg·m; 17 ft·lb

Service Data

The Honda 4-stroke or an equivalent (SE or later) oil with a viscosity of SAE 10W-30 is recommended for the GX390 K1, refilling oil capacity is 1.1 L (1.16 US. qt, 0.97 Imp. qt.). Recommended spark plug is NGK: BP6ES, BPR6ES; DENSO: W20EP-U, W20EPR-U with 0.7-0.8 mm (0.0276-0.0315 in) spark plug gap.

The valve clearance is 0.13-0.17 mm (0.0051-0.0067 in) for intake valves and 0.18-0.22 mm (0.0071-0.0087 in) for exhaust valves. Standard cylinder compression is 6.0-8.5 kg/cm2 (85-151 psi) at 600 rpm.

Maximum speed:3,850±150 rpm
Idle speed:1,400 ±150 rpm rpm
Cylinder compression:6.0-8.5 kg/cm2 (85-151 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:Splash type
Oil type:Honda 4-stroke or an equivalent (SE or later)
Recommended oil:SAE 10W-30
Oil capacity:1.1 L (1.16 US. qt, 0.97 Imp. qt.)
Fuel system
Type:Horizontal type carburetor with butterfly valve
Main jet: Externally vented: #105
Internally vented: #115
Float height:13.2 mm (0.5197 in)
Pilot screw opening: Externally vented: 2-1/4 turns out
Internally vented: 2-1/4 turns out
Ignition system
Type:Transistorized magneto ignition
Ignition timing:B.T.D.C. 25° (Fixed)
Spark plug: NGK: BP6ES, BPR6ES
Spark plug gap:0.7-0.8 mm (0.0276-0.0315 in)
Ignition coil air gap0.2-0.4 mm (0.008-0.016 in)


Manufacturer or BrandModels
HondaEB6500, EB6500X, EB6500SX, EB7000i, EC5000, EC6000, ECT6500, ECT7000, ECT7000P
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.

1 Comment

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