The Honda G300 is a 272 cc (16.6 cu.in.) single-cylinder air-coolled 4-stroke internal combustion small gasoline engine manufactured by Honda Motor Company since 1978 for general-purpose applications.
The Honda G300 engine has a slide valve (L-head) design and camshaft driven by a single row chain driven by the crankshaft. The engine has an electric or recoil starter, horizontal carburetor with butterfly valve and transistorized magneto or contact point breaker (CDI) ignition system.
Cylinder bore and piston stroke are 76.0 mm (3.0 in) and 60.0 mm (2.4 in), respectively. The compression ratio is 6.5:1. The G300 produced 7.0 HP (5.22 kW) at 3600 rpm of maximum horsepower and torque was 14.7 Nm (1.5 kg·m) at 3600 rpm. The dry weight of the Honda G300 with electric starter engine was 25.0 kg (55.1 lbs.), with recoil starter 22 kg (49 lbs.)
General information
| Engine Specifications | |
| Model | G300 |
| Type | 4-stroke, side valve type (L-head), single cylinder |
| Displacement | 272 cm 3 (16.6 cu-in) |
| Max. horsepower | 7.0 HP (5.22 kW) at 3600 rpm |
| Max. torque | 14.7 Nm (1.5 kg·m) at 3600 rpm |
| Carburetor | Horizontal, butterfly valve |
| Cooling system | Forced-air |
| Ignition system | Transistorized magneto or CDI |
| Lubricating system | Splash system |
| Starting system | Recoil or electric starter |
| Stoping system | Ground switch |
| Fuel used | Unleaded gasoline (octane number 86 or higher) |
| Fuel tank capacity | 6.0 L |
| Fuel consumption | 285 g/HPh |
| PTO shaft rotation | Counterclockwise (from PTO shaft side) |
Cylinder Block and Head
| Cylinder block | ||
| Compression ratio: | 6.5:1 | |
| Bore x Stroke | 76 X 60 mm (3.0 x 2.4 in) | |
| Sleeve internal diameter | 76.000-76.017 mm (2.9921-2.9928 in) | |
| Piston skirt outer diameter | 75.97-76.00 mm (2.991-2.992 in) | |
| Number of piston rings (compression / oil): | 2 / 1 | |
| Ring side clearance | Top | 0.02-0.06 mm (0.0008-0.0024 in) |
| Second/oil | 0.01-0.05 mm (0.0004-0.0020 in) | |
| Ring end gap | Top/second | 0.2-0.4 mm (0.008-0.016 in) |
| Oil | 0.2-0.4 mm (0.008-0.016 in) | |
| Ring width | Top/second | 1.97-1.99 mm (0.0776-0.783 in) |
| Oil | 3.97-3.99 mm (0.1563-0.1571 in) | |
| Connecting rod small end ID | 16.005-16.020 mm (0.6301-0.6307 in) | |
| Crankpin outer diameter | 29.943-29.959 mm (1.1789-1.1795 in) | |
| Cylinder Head | ||
| Warpage (limit) | 0.10 mm (0.004 in) | |
| Valve Arrangement: | Side valve type | |
| Valves: | 2 | |
| Stem outer diameter (standard): | INTAKE | 6.955-6.970 mm (0.2738-0.2744 in) |
| EXHAUST | 6.910-6.925 mm (0.2720-0.2726 in) | |
| Guide internal diameter | INTAKE / EXHAUST | 7.00-7.015 mm (0.2756-0.2762 in) |
| Spring free length | 42.7 mm (1.6811 in) | Cam height: | INTAKE | 38.46-38.72 mm (1.5142-1.5244 in) |
| EXHAUST | 38.49-38.75 mm (1.5154-1.5256 in) | |
Maintenance data
| Engine | |
| Idle speed | 1400 ± 150 rpm |
| Cylinder compression | 5.3 kg/cm2 (75 psi) |
| Adjust timing ignition | |
| Ignition timing | 20° B.T.D.C. – for magneto ignition The CDI type does not require adjustment. |
| Adjust valve clearance | |
| Intake valve | 0.08-0.16 ± 0.02 (0.0031-0.0063 in) |
| Exhaust valve | 0.11-0.19 ± 0.02 (0.0043-0.0075 in) |
| Oil system | |
| Oil type | Honda 4-stroke “SE” |
| Recommended oil | 10W-40 |
| Oil capacity | 1.2 L (2.54 US pt.) |
| Carburetor | |
| Main jet | #88 |
| Float height | 8.2 mm (0.32 in) |
| Ignition system | |
| Spark plug | NGK: B4H, BR4HS for magneto ignition NGK: BP4HS-10, BPR4HS-10 for CDI ignition |
| Spark plug gap | 0.6-0.7 mm (0.024-0.028 in), for magneto ignition 0.9-0.10 mm (0.035-0.039 in), for CDI ignition |
Tightening torque specs
| Tightening torque specs | |
| Fuel valve (12 mm) | 12-15 Nm; 1.2-1.5 kg·m; 8.7-10.8 ft·lb |
| Flywheel (16 mm) | 110-120 Nm; 11.0-12.0 kg·m; 80-87 ft·lb |
| Cylinder head | 24-26 Nm; 2.4-2.6 kg·m; 17-19 ft·lb |
| Tappet cover (6 mm) | 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb |
| Crankcase cover (8 mm) | 20-24 Nm; 2.0-2.4 kg·m; 15-17 ft·lb |
| Connecting rod | 12.6-15.4 Nm; 1.26-1.54 kg·m; 9.1-11 ft·lb |
| Fuel tank (8 mm) | 20-28 Nm; 2.0-2.8 kg·m; 15-20 ft·lb |
| Oil drain plug | 15-25 Nm; 1.5-2.5 kg·m; 11-18 ft·lb |
| Others | |
| 5 mm bolts, nuts | 4-7 Nm; 0.4-0.7 kg·m; 2.9-5.1 ft·lb |
| 6 mm bolts, nuts | 8-12 Nm; 0.8-1.2 kg·m; 5.8-8.7 ft·lb |
| 8 mm bolts, nuts | 20-28 Nm; 2.0-2.8 kg·m; 14.5-20.3 ft·lb |
| 10 mm bolts, nuts | 35-40 Nm; 3.5-4.0 kg·m; 25-29 ft·lb |
Author:
i am in need of G300 engine in volume, however, i want to know where and how to get it ( country and price ) regards
We are not a trading company, it`s only information site with engine specifications.
I have an early model g300 in working condition. You can have it if you prepay for shipping from FL usa. Needs some carb work and general TLC.
i need it
Do you still have the honda G300 engine? I am interested. mhedberg@msn.com
Hi are you still looking for the G300 honda engine? I have one please get in touch if interested still.
i need it. thanks
Yes I need it if you still have it.
Mail to me at twins4great@gmail.com
Thanks
I’ve got a good g300 for sale runs like a top $2000 obo
Apparently it is a trading platform!
hi, just wondering what the size of the shaft is for a pully please..looks like 26mm can anyone confirm.. many thanks
What is the out put shaft diameter? My buddy has one and he needs to buy a new Centrifugal clutch.
I have one of these G300 engines with a brand new carb and fresh oil regularly. It runs smooth and starts so easy, my 9-year old can start it. I am in Thunder Bay, Ontario, Canada. It’s for sale at $250 CAD.
The output shaft is 1″ diameter (25.4mm exactly). I also have 2-pulleys included with the motor, one 3″ and the other 3.5″.
The engine can be heard running. If you are interested and serious, we could facebook video chat and I can show you it cold start and running.
Is this engine still around? I am near Barrie .
Anyone know what electric starter is used on this motor? Mine is broken and the ID plate is damaged and unreadable.
I am seeking a replacement 12V starter.
Any help appreciated.
Hi did you finde the starter I’m looking for one also if where and do you have the part number
I have an older G300 Honda 7.0hp and one of the magnets on the inside of the flywheel rusted off. or i should say the bracket holding it on and the magnet is slightly broken. There are 4 total magnets on the inside all at 90 degrees. can this run with 3 magnets? do I need that forth? anyone know?
you can contact me directly at perrycaruso1575@gmail.com if you have a response or answer to my question on whether a G300 will run with only 3 magnets in the flywheel
I have this engine for sale for 200 runs good you can email me at ramsell6869@gmail.com
Is this the old points or cdi motor