Choosing an outboard motor for a small inflatable boat or a lightweight aluminum boat always involves finding a balance between power, weight and cost. Johnson 8bhp engine. It stands out as one of the most popular options in the used appliance market, and has for decades established itself as an "unkillable" workhorse that can confidently glid small craft.
The popularity of this power plant is explained by the simplicity of the two-stroke design, which allows owners to independently conduct most types of maintenance. However, despite the reliability, buying a mileage motor requires careful inspection, since the resource of the units depends on the quality of the mixture and storage conditions. Johnson 8 hp.
It's worth noting that despite the age of many of these engines, they continue to be used by fishermen and tourists, and their design simplicity makes repairs available even in the field, and spare parts can be found in almost any specialty store or at showdowns, making the model popular even in today's economy.
Specifications and engine design
At the heart of this model is the classic two-stroke water-cooled internal combustion engine, which is designed to be a vertical cylinder-wielding unit with loop purges, with a displacement of 196 cubic centimeters, which, when properly tuned, can remove the declared power of 8 horsepower.
An important feature is the ignition system, which may have differed from year to year, with older versions having a contact system (magdino) requiring regular cleaning and adjustment of the gap, while later versions have received a maintenance-free electronic ignition CDI. Lubrication system It is implemented by adding oil to gasoline, which is typical for two-strokes in this class.
The engine transmission has one front gear and neutral, as well as reverse. Switching is done manually through the humming wheel, which provides direct mechanical communication of the operator with the mechanism. The engine weight as standard is about 26-28 kilograms, which allows it to be transported in the trunk of a passenger car without the use of a special trolley.
Features of the cooling system
The cooling system uses a centrifugal pump with a rubber impeller located in the lower unit.
To understand the scale of the specifications, let’s compare the main parameters with the analogues of that time in the table below:
| Parameter | Johnson 8bhp. | Yamaha 8bhp (2T) | Mercury 8 hp |
|---|---|---|---|
| Workload | 196 cm3 | 196 cm3 | 196 cm3 |
| Number of cylinders | 2 | 2 | 2 |
| Weight (kg) | 26-28 | 27 | 27 |
| Launching system | Manual | Manual | Manual |
Rotor selection and speed specifications
The efficiency of the engine depends on the right propeller. Factory equipment often involves a screw with a pitch oriented to the average load, but for specific operating conditions it may need to be replaced. The optimal full gas speeds for this engine are in the range of 4500-5000 rpmThe propeller must allow the motor to reach these values.
If the engine is not turning at maximum speed ("not spinning"), it indicates too much pitch or overloading the boat. In this situation, the engine is running in overload mode, which leads to rapid loading and failure of the piston group. Conversely, if the motor easily goes to 6000+ rpm, the pitch of the screw is too small, and you do not use all the power.
For inflatable boats with a length of 2.8-3.2 meters with one passenger, the standard propeller is usually ideal. However, when increasing the load or using boats with a hard bottom and keel, the screw pitch may require a reduction.
Speed rates will vary depending on the hydro-aerodynamics of the hull. On a light inflatable boat with one person, you can reach speeds of up to 25-28 km / h. When fully loaded, the speed will drop to 15-18 km / h, which, nevertheless, remains sufficient for confident glides.
Fuel consumption and preparation of the mixture
Two-stroke engines are known for their appetite, and Johnson 8 hp The average fuel consumption when driving in a semi-lane (about 3000-3500 rpm) is about 2.5-3 liters per hour. At full gas, consumption can increase to 3.5-4 liters, so the fuel supply should always be in reserve.
The critical point is to prepare the fuel mixture: for break-in engines and normal operation, the recommended ratio is 1:50 (2% oil), that is, 20 ml of oil per 1 liter of gasoline. For new or newly repaired engines during the break-in period (the first 10 motor hours), the mixture is made richer - 1:33 or 1:40.
⚠️ Attention: Never use pure gasoline! The lack of oil in the mixture is guaranteed to lead to pistons bullying and engine wedge after a few minutes of operation. It is also dangerous to use old gasoline (stored for more than 3 months), as it loses its octane number and forms resinous deposits.
Only special two-stroke oils with labeling should be used. TC-W3The use of oils for trimmers or motoblocks (JASO FD and analogues) is unacceptable, since they are not designed to work in an aqueous environment and form a lot of sodium clogging the exhaust channels.
Use a transparent measuring tank to mix oil and gasoline. You can't tell the right proportion by eye, and an oil dosage error is expensive to fix.
Service and seasonal maintenance
Regular maintenance is the key to a long life for your child boat-engineThe owner must inspect the main components before each season and after every 50-100 hours of motorized maintenance, including replacement of the spark plug, inspection of fuel filters and lubrication of the units.
Special attention should be paid to the cooling system. After each operation in salt water or water with a large amount of suspension (silt, sand), it is recommended to wash the engine with fresh water, this will prevent corrosion of the water jacket and acidification of the thermostat (if it is provided by the design of a specific modification).
For high-quality maintenance, it is recommended to adhere to the following checklist:
☑️ Seasonal engine maintenance
The grease of the paddle shaft bearing is made through the press oil with a special water-resistant lubricant (usually red or green), this should be done regularly, since water through the osteoils can penetrate into the lower unit, causing corrosion of the gears of the gear gear gears.
Typical malfunctions and methods of their elimination
Despite reliability, problems can occur in operation. The most common complaint of owners is the lack of a spark or its weakness. In systems with magdinos, the interrupter contacts often oxidize or the capacitor fails. In electronic systems (CDI), the ignition coil or Hall sensor most often suffers.
The second common problem is loss of traction or inability to develop revs. This is often due to clogging of carburetor's jelly or sucking air through gaskets. Two-stroke engines are very sensitive to tightness of the intake tract. Even a microscopic crack in the crankshaft odule can lead to impoverishment of the mixture and overheating of the piston.
⚠️ Attention: If the engine suddenly stalls and doesn't start, don't try to spin it with a starter indefinitely. First, check for sparks and fuel. "Pouring" the candle with gasoline will only make things worse.
The third important node is diewuk, and knocking or noise when working can indicate the production of gears or bearings, and cutting of veneers on the propeller shaft is also common, especially when winding fishing nets or hitting underwater obstacles.
Compatibility with PVC boats and boats
8 horsepower is borderline for many types of boats. For PVC inflatable boats, it is often the maximum power allowed, making the motor the ideal choice. It allows for planing with 2-3 passengers, which is critical for fishing or recreation.
For lightweight aluminum boats such as Kazanka or Wind (small modifications), this engine is also well suited. However, for heavier hulls with a flat bottom and a large passenger capacity of 8 hp, it may not be enough to smoothly planing, and the boat will operate in displacement mode, consuming fuel inefficiently.
The Johnson 8 hp engine is the middle ground for boats ranging in length from 2.8 to 3.6 meters. It provides planing where 5 hp can no longer cope, but does not yet require registration with GIMS (depending on the total weight of the boat in charge).
When choosing a transom, it is important to consider the length of the lower unit. Most inflatable boats use a short leg (S - 381 mm), whereas keel boats and boats may require a long leg (L - 508 mm). Installing a short motor on a high transom will lead to cavitation and overheating, and a long one on a low - to increased water resistance.
FAQ: Frequently asked questions
Which petrol is best used for Johnson 8 hp?
It is recommended to use unleaded gasoline with an AI-92 or AI-95 octane number. The main requirement is freshness of the fuel. Gasoline should be free of alcohol additives, which can aggressively affect rubber carburettor seals.
Do I need to register a boat with this engine?
Registration with GIMS depends on the total weight of the boat in running order: if the total weight of the boat, engine, equipment and passengers exceeds 200 kg, or the engine power exceeds 8 hp (in some interpretations 8.0 hp is a boundary value, often 8.0 and below does not require category rights, but the registration of the vessel may require).
Why does the engine smoke at idle speed?
Heavy smoke on singles is a common phenomenon for two-strokes, especially if the proportion of oil is slightly disturbed upwards, or the candles have a soak. If the smoke is black and caustic, the mixture is too rich (a lot of oil or problems with the carburetor). If the smoke is white and steam, it is normal for cold weather (condensation).
Where to find spare parts for old Johnson models?
Since the Johnson brand is no longer manufactured under that name (production stopped or renamed Evinrude/BRP), many parts are unified. Carburetors, gaskets, glands and piston groups often fit with other OMC models of the period.