The 4 stroke engine – Breaking Down the Basics

One of the simplest forms of the internal combustion engine, the 4 stroke engine is a tremendously popular set up for vehicles that require a considerable amount of power and torque. This is the kind of performance that a two-stroke engine simply wouldn’t have been able to produce.

The beautiful thing about four stroke engine composition is that it follows along with the “golden rule” of internal combustion engine power. It allows more oxygen to mix with more fuel, which (in turn) results in better performance.

Another big advantage to using a 4 stroke set up is that it is pretty simple and straightforward to operate, maintain, repair, and replace. Sure, it has considerably more moving parts and components than a two-stroke engine (obviously), but it isn’t exactly rocket science to work on. They are relatively easy to repair or to completely overhaul.

If you’re interested in learning just a bit more about this amazing internal combustion engine design, we are going to include some basics and some “insider information” to help get you on your way to becoming at least a little bit more knowledgeable about this set up.

Breaking down the major components of a 4 stroke engine

Like every other internal combustion engine out there, there are going to be a handful of “key components” that make the power and performance possible in a 4 stroke engine.

We are talking about components like the:

• Flywheel
• Crank
• Connecting rods
• Pistons
• Intake valves/exhaust valves
• Intake cams/exhaust cams
• Spark plugs

          Though each and every one of these components are absolutely necessary for an engine like this to operate exactly as intended, we are only going to touch on some of the most important components. We will be discussing the “heartbeat” components. Hopefully this will give you a solid overview of what really makes one of these engines tick.

The intake/exhaust valves

Both of these valves are critically important to proper combustion in the engine. Each one of them is dependent entirely upon the camshaft and the way that it rotates (as well as the synchronicity of the rotation).

Oxygen is absolutely necessary for proper combustion of fuel in an internal combustion engine. You’re going to need both a way to pull air into the engine as well as a way to exhaust air after combustion has occurred. That is exactly the role that both of these valves play.

4 stroke engine color diagram

The crankshaft

One of those “meat and potato” components of almost any engine, the crankshaft is in the lower area of the engine. It holds the pistons (with connecting rods) together and has a flywheel at one end.

As the crankshaft turns or rotates, different Pistons are going to be responsible for compressing the fuel/air mixture inside of a chamber. Other pistons are waiting to be “pumped” after that compressed mixture explodes from the triggering of the spark plug.

And when the other pistons are pumped, the pistons are going to shift places, and the “dormant” pistons are then going to be responsible for compressing the fuel/air mixture. The engine repeats this cycle over and over all based on the movement and rotation of the crankshaft.

The faster the crankshaft moves, the faster these pistons begin to go through the motions of internal combustion and the faster that your vehicle moves.

It’s a beautiful ballet of machinery.

flathead 4 stroke

The four strokes of a four stroke engine

Now we are going to cover a very, very general overview of how a 4 stroke engine actually works by breaking down each of the four strokes.

The first stroke is an intake stroke.

What’s going to happen here is one of your pistons is going to move downward while the intake valve opens up to flood the combustion compartment with the right mixture of fuel and air while at the same time closing up the exhaust valves.

When the first intake stroke piston reaches its lowest possible position, the intake valve closes because of the rotation of the camshaft.

This creates the second stroke, the compression stroke.

During the compression stroke both the intake and exhaust valves are completely closed, which causes the upward movement of the piston to compress the fuel air mixture. The compression ratio is of critical importance here, as it is going to determine just how much the fuel air mixture is compressed. This relates directly to your fuel efficiency, your power, your speed, and your torque.

After the compression stroke reaches maximum “pressure” the third stroke begins – the power stroke.

The power stroke happens when the piston reaches the top of the combustion chamber, maximizing combustible pressure in the chamber since both the intake and exhaust valves have remained closed the entire time. This is when the spark plug fires and ignites the mixture. This forces the piston to move back down to the lower end of the chamber.

As the piston moves to the bottom of the chamber, the rotation of the camshaft is going to open up the exhaust valve, finishing off the fourth stroke of a 4 stroke engine with the exhaust stroke.

This allows everything remaining in the chamber to exhaust out of the chamber completely, before the entire system rinses and repeats over and over again.

Filed in: Gasoline Engines
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