How a 4 Stroke Engine Works How a 4 Stroke Engine Works

Most commonly today, internal combustion engines in vehicles operate with a 4 stroke cycle. Passenger cars and trucks, motorcycles, aircraft, construction vehicles and numerous others feature the 4 stroke cycle to power their motor. The 4 strokes to the cycle are intake, compression, combustion and exhaust. Each cycle entails two rotations of the crankshaft for engines fueled by diesel and gasoline. Two Italians patented the engine type in the mid 1800s, but a German named Nicolaus Otto is credited with the engine cycle’s creation. Thus, it is also known as the Otto cycle. A 4 stroke engine is a marvel of mechanical prowess, and there are many systems and component parts that make it function properly. However, the general process of the 4 stroke cycle is remarkably simple. Understanding the cycle’s 4 strokes is key to knowing how the engine type works.

The 4 Strokes

Intake, compression, combustion and exhaust are the 4 strokes to the cycle that takes place continually as the engine runs. In practice, this cycle happens one after the next in every cylinder of the engine. A vehicle with 6 cylinders has this cycle working in 6 different locations simultaneously. In order to understand how it works, though, describing the process in one cylinder is sufficient.


The beginning of the cycle starts at what is known as top dead center. The first half rotation of the crankshaft pulls the piston downward inside the cylinder, reducing pressure inside. As the piston descends, the intake valve is pulled open, letting in a mixture of forced fuel and air.


The second half rotation of the crankshaft pushes the piston back up again inside the cylinder, compressing the fuel and air mixture as the intake valve closes.


The third half rotation of the crankshaft is called the combustion stroke. At the end of the compression stroke, a spark plug or heat generated from compression ignites the combustible mixture of fuel and air. This small explosion pushes the piston downward again in the cylinder through its power stroke.


The final stroke is known as the exhaust stroke. After the power stroke, the last half rotation of the crankshaft pushes the piston upwards in the cylinder for a second time, expelling the byproduct of the fuel and air combustion. As it pushes the piston up, the exhaust valve opens, letting it out.

A Vehicle’s Power

That is essentially how an internal combustion engine operates. As mentioned, it does this continually in as many cylinders as the engine possesses. Most vehicles have 4, 6 or 8 cylinders. The vehicle’s power is mostly attained during the power stroke or combustion stroke after the fuel and air mixture is compressed into a small space. Power to a vehicle is limited to how much air it can take in. This is why after market air intake systems are installed in some cars to give them more power.

The internal combustion engine involves a process of the precise and attuned movement of many working parts. If one component is off alignment or damaged, the whole cycle can be thrown off. In addition to the movement of the crankshaft and pistons, the valves must be precisely timed to open and close. After long use, the timing gets off and they must be readjusted. The buildup of residue can also affect their performance.

There are many more systems to a functioning internal combustion engine, but this accurately describes the continual process of the 4 stroke cycle which is instrumental to the engine type.

Got a New Project You're Proud of?

Post it on Your Projects!