Honda GXV390

Honda GXV390 vertical shaft engineThe Honda GXV390 is a 0.39 l (389 cc, 23.7 cu-in) air-cooled single-cylinder four-stroke internal combustion small gasoline (petrol) engine with vertical shaft manufactured by Honda Motor Company for general-purpose applications, such as commercial lawn and garden equipment, tractors, construction and industrial equipment, agricultural equipment, small vehicles.

The GXV390 engine has an OHV design with two valves; sophisticated air intake system; large capacity, multi-chamber exhaust system. The engine is equipped with a centrifugal mechanical governor, horizontal type carburetor with butterfly valve, transistorized magneto ignition system and recoil or electric starter.

The cylinder bore is 88.0 mm (3.46 in) and the piston stroke is 64.0 mm (2.5 in). Compression ratio rating is 7.7:1. The Honda GXV390 produces 13.0 HP (9.7 kW) at 3,600 rpm and 28.0 Nm (2.8 kg·m, 20.3 ft·lb) of torque at 2,500 rpm.

General information

Engine Specifications
Type4-stroke, OHV, single cylinder
Displacement389 cm 3 (23.7 cu-in)
Max. horsepower13.0 HP (9.7 kW) at 3600 rpm
Max. torque (crank PTO)28.0 Nm (2.8 kg·m, 20.3 ft·lb) at 2,500 rpm
CarburetorHorizontal type, butterfly valve
Cooling systemForced-air
Ignition systemTransistorized magneto ignition
Lubricating systemPressure and splash
Starting systemRecoil or electric starter
Stoping systemIgnition primary circuit ground
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity2.3 L (0.61 US gal, 0.51 lmp gal)
Fuel consumption313 g/kWh (230 g/HPh, 0.51 lb/HPh)
PTO shaft rotationCounterclockwise (from PTO shaft side)

Dimensions and Weight

Length, mm (in)430 (16.9)
Width, mm (in)385 (15.2)
Height, mm (in)410 (16.1)
Dry weight, kg (lb)33 (72.8)
weight, kg (lb)
34.5 (76.1)

Cylinder Block and Head

The Honda GXV390 has cast iron cylinder sleeve, ball bearing supported crankshaft, improved piston design, heavy duty balancer shaft. The piston has two compression rings and one oil ring. Precision camshaft design offers precise valve timing and optimal valve overlap for better fuel efficiency.

Cylinder block
Compression ratio:7.7:1
Bore x Stroke88 X 64 mm (3.46 x 2.5 in)
Sleeve internal diameter88.000 mm (3.4646 in)
Piston skirt outer diameter87.985 mm (3.4640 mm)
Number of piston rings (compression / oil):2 / 1
Ring side clearanceTop/second0.030-0.060 (0.0012-0.0024)
Ring end gapTop0.20-0.40 mm (0.0079-0.0160 in)
Second0.20-0.40 mm (0.0079-0.0160 in)
Ring widthTop1.160-1.175 mm (0.0457-0.0463 in)
Second1.160-1.175 mm (0.045-0.0463 in)
Piston pin outer diameter19.994-20.000 mm (0.7872-0.7874 in)
Connecting rod small end inner diameter20.005-20.020 mm (0.7876-0.7882 in)
Connecting rod big end inner diameter36.025-36.039 mm (1.4183-1.4189 in)
Crankpin outer diameter35.975-35.985 mm (1.4163-1.4167 in)
Cylinder Head
Warpage (limit)0.10 mm (0.004 in)
Valve Arrangement:OHV
Stem outer diameter (standard):INTAKE6.590 mm (0.2594 in)
EXHAUST6.550 mm (0.2579 in)
Cam height:INTAKE32.60 mm (1.283 in)
EXHAUST32.09 mm (1.263 in)
Camshaft outer diameter:16.000 mm (0.6299 in)

Tightening torque specs

Tightening torque specs
Connecting rod bolt14 Nm; 1.4 kg·m; 10 ft·lb
Cylinder head bolt35 Nm; 3.5 kg·m; 25 ft·lb
Flywheel nut115 Nm; 11.5 kg·m; 83 ft·lb
Pivot adjusting nut10 Nm; 1.0 kg·m; 7 ft·lb
Push rod guide pivot bolt24 Nm; 2.4 kg·m; 17 ft·lb
Oil pan bolt24 Nm; 2.4 kg·m; 17 ft·lb
Air cleaner body cap nut9 Nm; 0.9 kg·m; 6.5 ft·lb
Muffler mounting nut24 Nm; 2.4 kg·m; 17 ft·lb
Exhaust pipe mounting nut24 Nm; 2.4 kg·m; 17 ft·lb
Oil drain plug45 Nm; 4.5 kg·m; 34 ft·lb
Cylinder head cover bolt9 Nm; 0.9 kg·m; 6.5 ft·lb
Fuel tank bolt24 Nm; 2.4 kg·m; 17 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)24 Nm; 2.4 kg·m; 17 ft·lb
Bolt, nut (10 mm)37.5 Nm; 3.75 kg·m; 27 ft·lb
Bolt, nut (12 mm)55 Nm; 5.5 kg·m; 40 ft·lb

Maintenance data

Maximum speed3400 ± 150 rpm
Idle speed1400 ± 150 rpm
Cylinder compression5.0-8.5 kg/cm2 (71-151 psi) at 600 rpm
Valve clearance
Intake valve0.10 ± 0.02 (0.004 ± 0.001)
Exhaust valve0.15 ± 0.02 (0.006 ± 0.001)
Main jet#95
Float height11.9-14.5 mm (0.47-0.57 in)
Pilot screw opening2-1/2 turns out
Oil system
Oil typeHonda 4-stroke or an equivalent (SE or SF)
Recommended oilSAE 10W-40
Oil capacity1.1 L (1.2 US gal, 1.0 lmp qt)
Ignition system
Ignition timing20 ° B.T.D.C (Fixed)
Spark plugNGK: BPR5ES
Spark plug gap0.7-0.8 mm (0.028-0.031 in)
Primary ignition coil resistance0.7-0.9 Ω
Secondary ignition coil resistance6.3-7.7 kΩ
Ignition coil air gap0.4 ± 0.2 (0.016 ± 0.008)
Starter motor
Brush length7.2 mm (0.28 in) limit: 3.5 mm (0.14 in)
Mica depth1.0 mm (0.04 in) limit: 0.2 mm (0.01 in)
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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  1. This engine uses throttle cable to adjust speed and to stop engine. I need a throttle lever and not throttle cable to adjust speed of the engine like on GX390, GX270 and so on.

  2. engine specs states this engine (gxv390) hp rating is 13.0, but the ferris fw15 mowers which use this engine state it is rated at 10.2 hp. which is correct ?

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