4 stroke engine

The 4-stroke engine is present in the vast majority of vehicles we are familiar with, whether in automotive, motorbike or marine applications.

It is a type of internal combustion engine and owes its name to its own operation, which occurs in four stages (called strokes). These four stages are intake, compression, combustion and exhaust.


4 stroke engine


How a 4-stroke engine works

The 4-stroke engines, both petrol and diesel, operate in the following stages:

  1. Intake: In this first stage, air and fuel are allowed to enter the engine cylinder. During the intake process, the air is filtered to remove any impurities and the fuel is injected or mixed with the air. The main agents performing these actions are respectively the air filter, the injector and the carburettor.
  2. Compression: In this second stage the piston moves upwards to compress the air-fuel mixture. The piston rings seal the gap so that the mixture does not escape from the sides of the cylinder.
  3. Combustion: This is the third stage, where the previously compressed mixture is set on fire, causing it to explode and push the piston down. In petrol engines this explosion is achieved by a spark caused by a spark plug. In 4-stroke diesel engines, however, the combustion phase is slightly different. Instead of using a spark to ignite the fuel-air mixture, the mixture is compressed until it is hot enough to ignite on its own. This process is called compression combustion.
  4. Exhaust: In this last stage, the exhaust valve opens, allowing the gases resulting from combustion to escape into the exhaust manifold and the exhaust pipe.
4StrokeEngine Ortho 3D Small

Zephyris, CC BY-SA 3.0, via Wikimedia Commons


Most important parts of a 4-stroke engine:

A 4-stroke engine is composed of several essential parts that work together to generate the power that drives the engine and thus runs the boat, vehicle or machine.

Some of the most important components are:

  1. Engine block:  It is the main structure of the engine, where the cylinders and other components are housed.
  2. Pistons: They are moving elements that move up and down inside the cylinders to convert chemical energy into mechanical energy.
  3. Crankshaft: It converts the linear motion of the pistons into a rotary motion.
  4. Camshaft: It controls the opening and closing of the intake and exhaust valves and is essential for engine operation.
  5. Stock: The upper part of the engine that covers the cylinders and contains the valves.
  6. Lubrication system: Set of elements that lubricate the moving parts of the engine to reduce wear. Choosing a good brand-recommended engine oil helps to extend the life of the equipment.
  7. Fuel system: Set of parts that provide the fuel-air mixture necessary for combustion in the cylinders.
  8. Cooling system: Keeps the engine temperature at a controlled level.


Key piece: How the crankshaft works.

The crankshaft, a key part located at the bottom of the engine block, plays an important role.

There are different variations of crankshafts depending on engine type and functionality, but in general it is a composite part based on a composite shaft with a series of counterweights on which a connecting rod is fitted.

Its main function is to convert the linear motion of the pistons into a rotary motion, so that it can move the propulsive line and turn the propeller (in the case of the marine engine) through the transmission.

The crankshaft is designed to withstand high loads and high rotational speeds, making it one of the strongest components in the engine.

It is also composed of a series of counterweights that help to balance the rotational movement and reduce vibrations. These counterweights are positioned in such a way that they counteract the forces generated by the pistons during their upward and downward movement. In addition, the bearings allow the crankshaft to rotate smoothly and with little friction.

On the other hand, it also has other parts such as the journals, which are the sections of the crankshaft that connect to the piston rods. These connecting rods are connected to the pistons and are responsible for converting the linear motion of the pistons into a rotary motion of the crankshaft.

In summary, the crankshaft is an essential component in the 4-stroke engine as it is responsible for converting the linear motion of the pistons into a rotary motion which is finally transmitted to the drive shaft. It is a part that requires high resistance and precision for its correct operation, and its design and construction are fundamental for the correct performance of the engine.


4 stroke engine


4 stroke marine engine: marinisation and features

The marinisation process consists of transforming an industrial combustion engine for operation in the marine environment.

One of the main differences is the operation of the cooling system. In the cooling system of an industrial engine, the engine coolant is cooled using a radiator. In this radiator, heat is exchanged between the coolant and the air, thus keeping the temperature of the coolant, and thus the engine, below the required values.

In the marine environment, instead of the radiator, a part called a cooler is used, which instead of exchanging heat with air, exchanges it with seawater. The coolant makes a closed circuit inside the engine. On the other hand, the seawater is absorbed by the salt water pump, fed into the cooler, heat exchanged and discharged through the exhaust together with the combustion gases. In no case does the coolant mix with the salt water, they are independent circuits.

In addition to the refrigeration system, in the development of a marinisation process, the fuel supply, gas intake and exhaust circuits, electrical system, support system, etc., are designed with the appropriate materials and characteristics to be able to operate in such an aggressive environment as the marine environment.

If you are thinking of changing the engine of your boat, at Solé we offer you a wide range of diesel inboard engines from 16 hp to 270 hp, reliable, robust, high performance, efficient and easy to maintain. Solé engines are suitable for all types of vessels such as sailboats, motor sailboats, fishing boats, llaüts and all other types of recreational and commercial vessels.

Contact your nearest Solé dealer without obligation and enjoy unlimited navigation with total confidence.


Repower with Solé and give your boat a new life.