How the 2-stroke engine works

The 2-stroke engine is, together with the 4-stroke engine, an internal combustion engine with a cycle of four phases of admission, compression, combustion and exhaust, like the 4-stroke, but all of them carried out in only 2 times, that is. , in two movements of the piston.

In a 2-stroke engine, an explosion occurs for each turn of the crankshaft, while in a 4-stroke engine, an explosion occurs for every two turns of the crankshaft, which means that for the same displacement, more power is generated , but also more fuel consumption. gas.

2-stroke engines have gradually been replaced by 4-strokes due to their more polluting nature and on motorcycles we only find it today in small-engine mopeds and some enduro or motocross motorcycles. A 2-stroke engine is simpler and lighter than a 4-stroke since it is made up of fewer parts, originally it does not use intake and exhaust valves, they are cheaper to manufacture and require less maintenance, but their higher rpm causes however increased wear.

The lubrication of a 2-stroke engine is included in the mixture and, together with gasoline and air , oil is added , which is why when it is burned it is much less respectful of the environment. Thus, the crankcase is sealed since it houses the entrance of the mixture and the two faces of the piston come into action, the upper one to compress the mixture and the lower one to cause its admission to the crankcase. We explain to you what are the steps of a 2-stroke cycle  thanks to this article .

2-stroke engine cycle

The times of this type of motor are 2 and each one performs a different function.

How does a two-stroke engine work?


two-stroke engine cycle In a 2-stroke engine, it is  the piston itself  that, with its movement, opens the intake of the mixture, at the level of the crankcase, and the exhaust of the burned gases, at the level of the combustion chamber.

Intake and compression are done  at the same time.

At time 1 the piston goes from bottom to top, that is, from the crankcase to the cylinder head. In its displacement it sucks the mixture of gasoline, air and oil in its lower part, while simultaneously it is in charge of compressing the mixture of the previous admission in the upper part.


The second stage begins with the piston located at its top dead center, compressing the mixture of gasoline, air and oil to the maximum, which makes their molecules collide more quickly and considerably increases the temperature of the mixture.

It is at that moment when  the spark plug generates a spark that sets the mixture on fire,  causing its combustion. This explosion causes the piston to move violently downwards, transmitting the movement to the crankshaft through the connecting rod, and with this movement leaves the exhaust open through which the recently burned gases are released.

But there is more, in this downward movement the piston pushes the new mixture that had entered in its previous rise, and  when it goes down it transfers the mixture from the crankcase to the combustion chamber , thus preparing the process to start over again in the first stage. previously described.

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What do you think? Has it helped you understand how a 2-stroke engine works ?

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