4 stroke motor: device, cycle of operation and maintenance

Modern water transport is impossible to imagine without a reliable source of energy, and it is the four-stroke engine It has become the gold standard for most small-size boat owners, and unlike its predecessors, these units provide quiet operation, high fuel efficiency and minimal environmental impact. For a boater, understanding how a motor works is not just a theoretical framework, but the key to good operation and timely maintenance.

Choosing between two-stroke and four-stroke is often the first and most difficult decision to make when buying. boat-engineThe four-stroke circuit, or Otto cycle, assumes that one cycle is completed in four strokes of the piston and two full rotations of the crankshaft, a fundamental difference that fundamentally changes the way we design, lubricate and repair machinery.

In this article, we will take a closer look at the internal structure of the motor, examine each stroke of operation and discuss the nuances that will help to extend the life of your engine, you will learn why such motors require less attention in daily operation, but are more difficult to repair.

The principle of operation and the four-stroke cycle

The heart of anyone. combustion engine It's a cylinder-piston group where the heat energy of a burning fuel is converted into mechanical motion. In a four-stroke engine, this process is strictly divided into four successive phases, each of which performs a critical function. Understanding these phases helps diagnose malfunctions by the sound and operation of the unit.

The first bar is called intake, at which point the piston moves from the top dead point (BMT) downwards, creating a vacuum in the cylinder. Intake valve It opens, and a fresh air/fuel mixture is sucked into the cylinder, and it's important to note that in carburetor engines, the carburetor motors are responsible for the formation of the mixture, and in injection engines, the nozzles that spray fuel directly into the intake manifold or cylinder.

⚠️ Warning: Never try to adjust valve gaps on a hot engine. The thermal expansion of the metal will distort measurements, leading to valve burnout or loss of compression after cooling.

The second stroke is compression. Both valves are closed, sealing the combustion chamber. The piston moves upwards, compressing the mixture, which leads to a sharp increase in temperature and pressure. At the end of this stroke, spark-plate It gives a spark that ignites the mixture, and the timing of the ignition is strictly regulated and depends on the engine speed.

The third stroke is the stroke. This is the only time the engine generates energy. The burning gases expand with great force, pushing the piston down. It's this motion through the rod that is transmitted to the crankshaft, causing it to rotate. The other three cycles are carried out by the inertia of the flywheel or the energy of other cylinders in multi-cylinder engines.

Fourth stroke, release. The piston moves up again, pushing the exhaust gases through the open. discharge-valve The exhaust system, which closes the cycle and repeats the process, depends on the timing of the distribution mechanism (GDM).

Key engine systems and gas distribution

The reliability of a four-stroke engine depends largely on a complex gas distribution system. Unlike two-strokes, where the windows in the cylinder are opened by the piston itself, here the timing of the opening of the valves is responsible for the timing (time) of the opening of the valves. gas-shaft It is driven by a chain, a belt or gears from a crankshaft.

The lubrication system in four-stroke engines is very different from two-stroke engines, where the oil is not mixed with gasoline, but is in a separate crankcase. A special oil pump under pressure provides lubrication to rubbing parts: root and rod bearings, pistons fingers and a pair of camshaft-pusher, which provides a long life of parts.

The cooling system is also critical. Most outboard motors use off-board water, which is pumped through the cooling shirt using the help of a water-powered engine. impeller Overheating is the main enemy of aluminum cylinder blocks, so controlling the water jet ("control") is mandatory at each start.

• 🔧 GRM: Ensures timely intake of the mixture and release of gases, requiring periodic check of the tension of the chain or belt.
• 💧 Lubricant: Uses pure engine oil, which is filtered and circulates in a closed circuit without burning in the cylinder.
• ❄️ Cooling: The thermostat regulates the temperature, opening a large circle of water circulation when the engine warms up.

The special attention should be paid to the crankcase ventilation system, because when the engine is running, some of the gases inevitably break through the piston rings into the crankcase, if left undisturbed, they mix with the oil to form an aggressive acid emulsion, and modern motors send these gases back into the intake for afterburning.

What is a hydroshock and how to avoid it?

A water shock is a fluid that enters the cylinder of an engine, and because the water is incompressible, when a piston tries to compress it, the motor stops immediately, often causing a rod or crankshaft to break, and on boats, this happens when you draw water sharply through the exhaust hole or when you dive deep into the transom.

Comparison: 4 bars vs. 2 bars

The two-stroke engine debates have been going on for years, and the two-stroke engines are simpler, easier and cheaper to manufacture, but they are much less resourceful and environmentally friendly, because some of the fuel just goes into the exhaust pipe with the oil.

Four-stroke engines are heavier and more expensive, but they provide stable torque at low revs, ideal for trolling and heavy planing boats. Not having to mix oil with gasoline makes refueling easier and reduces the risk of operator error.

Below is a table showing the key differences that will help you make the final choice when buying a machine.

Characterization	two-stroke engine	four-stroke engine
Fuel consumption	High (up to 30% of the mixture is burned in vain)	Low (economic regime)
Noise level	Tall, ringing.	Low, deaf.
Resource to overhaul	1,000 to 2,000 motor hours	3000-5000+ motor hours
Motor weight	Easy 15-20%.	It's heavier because of the complex design.
Service	Simple but frequent.	Harder, but less so.

It is worth noting that modern four-stroke motors have learned to be quite compact. DOHC (two camshafts) allows you to optimize the filling of cylinders, increasing power without increasing volume.

Fuel and oils: requirements and standards

The quality of fuel and lubricants directly affects the durability piston-groupFor four-stroke outboard motors, gasoline with an octane number specified in the instructions (usually an AI-92 or an AI-95) must be used. Using fuel with a lower octane number can cause detonation that destroys the pistons.

Motor oil is a science, and unlike cars, outboard motors often operate in extreme conditions: high speeds, water risk, long downtime. Oils must have appropriate tolerances, such as: NMMA FC-WThis is a standard designed specifically for four-stroke marine engines.

The viscosity of the oil is determined by the climatic zone, and for temperate climates, the most versatile choice is to choose from the most common. 10W-30 or 10W-40Synthetic bases better protect the engine in cold start and high temperatures, preventing the formation of bullies.

⚠️ Warning: Never use energy-saving car oils (labeled Energy Conserving) that can cause candles to foul and valves to burn when the outboard motor is running.

The oil replacement in a four-stroke engine is recommended every 50 to 100 hours or once a season, even if the mileage is small. The condensation that falls inside the crankcase at temperature changes turns into water that emulsifies the oil, turning it into "mayonnaise" - a substance that can not lubricate parts.

Running a new engine: rules and stages

The new four-stroke engine requires a mandatory break-in, and in the process of laundry, the piston rings are pressed against the cylinder walls, and all the moving elements occupy their working positions, neglecting this step reduces the engine life by many times and can lead to increased oil consumption in the future.

The break-in process usually takes about 10 hours. In the first two hours, it is recommended not to exceed 50% of the maximum power. The next 8 hours you can work at 70-80% of the power, avoiding long work at constant speeds. It is important to vary the load so that the rings are worn uniformly over the entire surface.

After the first 10 hours, the first maintenance is required. You need to replace the engine oil and the oil filter. After the break-in, the oil will contain a lot of metal shavings, which is a normal product of the finishing of the parts, you should also check the tightening of the mounting bolts and the condition of the candles.

Typical malfunctions and diagnosis

Even the most reliable four-stroke motor One of the most common problems is that there's no jet of water coming out of the control hole, which indicates that the pump is malfunctioning, that the water channels are clogging, that the impeller is damaged, and that if the engine is operated without cooling, it will overheat and jam the piston in minutes.

Another common problem is difficulty starting or idling, often caused by contaminated fuel injectors, spark plugs or air suction in the intake manifold, and the diagnosis begins with checking the spark and compression in the cylinders.

An outside knock in the engine is an alarm, a thud may indicate wear on the rod liners, and a ringing one may indicate a valve failure or detonation, and if there is a knock, the operation must be stopped immediately.

Electronics are also not uncommon.TPSThe temperature and pressure sensors can fail, putting the engine in emergency mode. Accurate diagnosis of modern injection motors requires the connection of a scanner.

Why doesn’t the engine develop full speed?

There may be several reasons: a contaminated fuel filter, low-octane fuel, an incorrectly installed ignition advance angle or overgrown lower unit shells, creating propeller resistance.

Seasonal storage and conservation

The best way to preserve it for the winter is to start in the spring, and the main thing is to protect the engine from corrosion and freezing of water, and the first thing you do is to drain all the water from the cooling system, and you take the engine off the boat or put it upright.

Then you have to preservative the internal cavities of the cylinders, and you twist the candle, you splash some oil into the cylinder, and you scroll the starter several times, and you spread the oil film across the walls, and then you twist the candle back.

The fuel system is better preserved by adding a fuel stabilizer to the tank and generating its residues, or completely emptying the system. Open metal parts, such as lower unit and fasteners, should be lubricated with a special lubricant to protect against moisture.

How to properly store a outboard motor in winter?

The motor should be stored in a dry, ventilated room, the optimal position is vertical, on a special rack. If the motor is stored on the transom of the boat, make sure that water cannot enter the exhaust hole and freeze, expanding and damaging the block.

Do I need to charge the battery in winter?

Yes, lead-acid batteries are prone to self-discharge, and once a month or a half they need to be recharged with a stationary charger to prevent plate sulfation and loss of capacity.

Can the engine be washed with water under pressure?

High pressure sinks (Karcher and analogues) are strongly discouraged; a powerful jet can damage the osteoils, drive water into electrical connectors and flush the grease off the rubbing nodes. Use a garden hose and a soft brush.

What to do if the engine is “boiled”?

If the overheating lamp is on or you hear a signal, immediately release the gas to a minimum and let the engine work on the idles for a couple of minutes to cool down. Abruptly stopping the hot engine can cause the block head to deform. Then check the cooling system for obstacles.

How often do I change the spark plugs?

In four-stroke outboard motors, candles are recommended to be changed every 100 hours or once a season, even if they look normal.