Piston Engine

In a piston engine, exploding fuel pushes the pistons up and down inside cylinders, and that up-and-down movement cranks over a shaft called the driveshaft. Like your hand turning a crank to open a window, the cranking motion is used to move your car. As the piston comes up it squeezes air and fuel trapped in the top of the cylinder, and when the air/fuel mix explodes it pushes the pison back down.

Like any combustion engine, a rpiston engine needs air, fuel, and compression (to squeeze the air & fuel, heating it up) Gasoline engines need a spark to ignite the air and fuel, but diesel engines just squeeze the fuel harder until it ignites. Most cars on the road today have piston engines, including deisel powered cars, though a select few of them have a rotary engine instead, which works a bit differently.

Virtually all car engines are ‘four stroke’ engines. This refers to how many changes of direction the piston makes during one power-producing cycle (the piston actually cranks over the crankshaft to make your car move only on every 4th stroke). The cycles are often divided into strokes, with each stroke is motion in one direction. An easy way to remember how it works is with the phrase “suck, squeeze, bang, blow”:

Intake (“Suck”)

This is considered the first movement of the piston, and is a downward motion of the piston that sucks cool, clean air into the cylinder from the outside. Fuel is mixed with the air as a fine mist either just before or just after the air enters the cylinder, depending on the engine design. In a carbureted system the air is drawn first through the carburetor, mixing with atomized gasoline, then into the engine. In a fuel injection system the injectors squirt a stream of atomized fuel into the intake manifold where it mixes with the air rushing past on its way into the engine.

The suction is created in the same way as a syringe draws in liquid when the plunger is pulled out. The air and fuel mixture is drawn into the cylinder through an open intake valve.

Compression (“Squeeze”)

The intake valve closes, sealing the cylinder so no gasses can get out. The piston is pushed up by the crankshaft and squeezes, or compresses, the air and fuel mixture. All this squeezing makes the air/fuel mix very hot and ready to explode.

Combustion (“Bang”)

With the air/fuel mix compressed into a small, hot space the spark plug fires and ignites an explosion. The force of the resulting boom pushes against the top of the piston, which plunges down and powerfully turns the crank shaft. This is what actually turns your engine and makes your car go!

Exhaust (“Blow”)

The crankshaft, pushed around to the bottom by the combustion stroke, starts coming back up again. This pushes the piston back up. The exhaust valve opens and lets the burnt up gasses push out of the cylinder rather than compressing them again.

As the cylinder reaches the top the intake valve opens to start it all over again.

Valves

The valves are opened and closed by a camshaft, a spinning shaft that pushes on them. Overhead cam engines use camshafts located above the cylinder head, instead of the traditional location inside the engine block. This eliminates the use of push rods and rockers, creating a ‘tighter’ valve train that doesn’t ‘float’ or rattle around as much. Overhead cam engines can operate more efficiently at higher engine speeds than pushrod types.

Gaskets

You may have heard the expression “blown a gasket” before – but what are gaskets?

When two pieces of metal are bolted together, the microscopic differences between the two surfaces prevent them from pressing together absolutely flat. These gaps happen no matter how precisely the metal is machined, and can change as the metal heats up and cools. When you’re trying to keep hot gasses trapped in a cylinder or engine coolant or oil from leaking out of the engine, it’s important that the gaps be filled in.

Gaskets are thin sheets of flexible materials that are used to fill in these gaps. They allow metal parts to be bolted together without leaking the fluids that are transferred between the two. Gaskets are commonly made from brass, steel, rubber, and even paper compounds. In addition to proving more conductive passages for fluids to flow, they also serve as insulation to isolate some parts from shock or vibrations that could cause leaks, and create tighter fitting parts that are more likely to stay in place.