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In its basic form, a combustion engine is a rather crude way of generating energy. It’s essentially a bunch of explosions happening inside a hollowed-out piece of iron. But take a closer look, and you’ll quickly learn how refined an engine really is.

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An engine makes 4 complete strokes for each complete engine cycle. Nearly all modern engines are four-stroke engines. Four-stroke refers to how many times a piston must travel up and down inside a cylinder to complete a full engine cycle. The engine draws in precise, micron-measured amounts of fuel and air through valves, compresses them, combusts them, and releases them. These 4 strokes are commonly referred to as suck, squeeze, bang, and blow.

• Intake Stroke. The intake valve opens, and the piston moves downward to suck in air while the fuel injector introduces fuel.
• Compression Stroke. The intake valve closes, and the piston travels upward to squeeze the fuel and air mixture.
• Combustion Stroke. The spark plug fires, creating an explosive bang in the chamber. This drives the piston down, releasing the energy required to move the automobile.
• Exhaust Stroke. The exhaust valve opens, and the piston travels upward to blow the burned fuel and air mixture out of the cylinder, through the exhaust manifold, catalytic converter, and muffler, and out the tailpipe.

The pistons in the engine all work in sync to provide ongoing rotational force. Each piston is attached to the crankshaft, which is attached to the drivetrain that moves the vehicle. Depending on how many cylinders the engine has, the firing order of the cylinders varies.

The valves, which regulate the intake and release of air, fuel, and exhaust, also operate in sync. They are controlled by a camshaft, which is attached to the crankshaft by a timing chain or timing belt for proper piston and valve positioning. This is critical, because without a timing chain or belt, valves and pistons can’t operate properly and can potentially collide with each other, causing serious engine damage.