Honda G80

Honda G80 engineThe Honda G80 is a 296 cc (18.0 single-cylinder air-coolled 4-stroke internal combustion small gasoline engine manufactured by Honda Motor Company since 1975 for general-purpose applications.

The Honda G80 engine has a slide valve (L-head) design and camshaft driven by a single row chain driven by the crankshaft. The engine has a recoil starter, horizontal carburetor with butterfly valve and high voltage ignition.

An 80.0 mm (3.2 in) cylinder bore and 59.0 mm (2.3 in) piston stroke give the engine a total of 296 cc (18.0 of displacement. The compression ratio was 6.3:1. The G80 produced 8.0 HP (5.9 kW) at 4000 rpm of maximum horsepower and continuous rated output was 6.0 HP (4.5 kW) at 3600 rpm. The maximum torque was 15.7 Nm (1.6 kg·m) at 2500 rpm. The dry weight of the Honda G80 engine was 30.4 kg (67.0 lbs).

General information

Engine Specifications
Type4-stroke, side valve type (L-head), single cylinder
Displacement296 cm 3 (18.0 cu-in)
Max. horsepower8.0 HP (5.9 kW) at 4,000 rpm
Max. torque15.7 Nm (1.6 kg·m) at 2,500 rpm
CarburetorHorizontal, butterfly valve
Cooling systemForced-air
Ignition systemHigh voltage ignition
Lubricating systemSplash system
Starting systemRecoil starter
Stoping systemGround switch
Fuel usedUnleaded gasoline (octane number 86 or higher)
Fuel tank capacity6.9 L (1.8 US gal., 1.5 Imp. gal.)
Fuel consumption285 g/HPh
PTO shaft rotationCounterclockwise (from PTO shaft side)

Cylinder Block and Head

Cylinder block
Compression ratio:6.3:1
Bore x Stroke80 X 59 mm (3.2 x 2.3 in)
Sleeve internal diameter80.00 mm (3.150 in)
Piston skirt outer diameter79.97 mm (3.148 in)
Ring widthTop2.48 mm (0.098 in)
Second/Oil2.49 mm (0.098 in)
Ring Side ClearanceTop0.02 mm (0.0008 in)
Second/Oil0.01 mm (0.0004 in)
Piston pin outer diameter19.0 mm (0.748 in)
Cylinder Head
Warpage (max)0.2 mm (0.01 in)
Valve Arrangement:Side valve type (L-head)
Stem outer diameter (standard):INTAKE6.97 mm (0.274 in)
EXHAUST6.93 mm (0.273 in)
Valve guide internal diameter7.00 mm (0.276 in)
Cam height:INTAKE35.18 mm (1.385 in)
EXHAUST35.18 mm (1.385 in)

Maintenance data

Cylinder compression4.0 kg/cm2 at 450-600 rpm
Tappet clearance
Intake valve0.06-0.11 mm (0.0023-0.0043)
Exhaust valve0.06-0.11 mm (0.0023-0.0043)
Oil system
Oil typeHonda 4-stroke or an equivalent (SG, SF)
Recommended oilSAE 10W-30, 10W-40
Oil capacity1.1 L (2.3 US pt, 1.9 lmp pt)
Ignition system
Ignition timing25 ° B.T.D.C (Fixed)
Spark plugNGK: BR6HS, B6HS
Spark plug gap0.6-0.7 mm (0.024-0.028 in)

Tightening torque specs

Tightening torque specs
Fuel tank (8 mm nut, bolt)20-28 Nm; 2.0-2.8 kg·m; 14.5-20.2 ft·lb
Side cover (10 mm bolt)35-40 Nm; 3.5-4.0 kg·m; 25.3-28.9 ft·lb
Cylinder Head (10 mm bolt)35-40 Nm; 3.5-4.0 kg·m; 25.3-28.9 ft·lb
Cylinder (6 mm bolt)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Cylinder (8 mm bolt)20-28 Nm; 2.0-2.8 kg·m; 14.5-20.2 ft·lb
Camshaft center (6 mm bolt)10-15 Nm; 1.0-1.5 kg·m; 7.2-10.8 ft·lb
Starter pulley (6 mm bolt)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Flywheel (17 mm nut)70-80 Nm; 7.0-8.0 kg·m; 50.6-57.9 ft·lb
Muffler (6 mm nut)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
Muffler (8 mm bolt)20-28 Nm; 2.0-2.8 kg·m; 14.5-20.2 ft·lb
Carburetor (6 mm nut)8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb
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 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.

1 Comment

  1. Thank you for compiling this wealth of technical information and publishing it on this site. It is very, very useful. Such information is also becoming increasingly harder to find, in general, as the years pass. Your site is a fine example of what the Internet *should* have become. Conversely, It has sadly become all but worthless in recent years. But it’s nice to know that some folks are still doing things right.

    I’m definitely going to bookmark this site, as I work on sll manners and sizes of engines. Today it happens to be an old Honda G80… And, somehow I actually found your site, replete with all the information I needed. As such, I figured the least I could do was take a couple minutes to leave this message. Credit where due.

    Again, thank you.

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