• Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.
   

• You might want to know what's going on in there simply out of curiosity. After all, you ride in your car every day.
   

• Wouldn't it be nice to know how it works?
   

• Or perhaps you are buying a new car, and you hear funny words like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection".

What does all of this mean?

• The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline.
   

• This is the intake stroke.
   

• Only the tiniest drop of gasoline needs to be mixed into the air for this to work (Part 1 of the figure).
   

• Then the piston moves back up to compress this fuel/air mixture.
   

• Compression makes the explosion more powerful. (Part 2 of the figure)
   

• When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline.
   

• The gasoline charge in the cylinder explodes, driving the piston down (Part 3 of the figure).
   

• Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tail pipe. (Part 4 of the figure).
   

• Now the engine is ready for the next cycle, so it intakes another charge of air and gas.
   

• Notice that the motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear (straight).
   

• In an engine the linear motion is converted into rotational motion by the crank shaft.
   

• The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.

Engine Definitions

• Cylinder
  The core of the engine is the cylinder. The piston moves up and down inside the cylinder. The engine described here has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.

Inline - The cylinders are arranged in a line in a single bank.

V - The cylinders are arranged in two banks set at an angle to one another.

Flat - The cylinders are arranged in two banks on opposite sides of the engine.

• Spark Plug
  The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.
   

• Valves
  The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.
   

• Piston
  A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
   

• Piston Rings
  Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes.
   

• They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
   

• They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.
   

• Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.
   

• Combustion Chamber
  The combustion chamber is the area where compression and combustion take place. As the piston moves up and down, you can see that the size of the combustion chamber changes. It has some maximum volume as well as a minimum volume. The difference between the maximum and minimum is called the displacement and is measured in liters or CCs (Cubic Centimeters, where 1,000 cubic centimeters equals a liter). So if you have a 4-cylinder engine and each cylinder displaces half a liter, then the entire engine is a "2.0 liter engine." If each cylinder displaces half a liter and there are six cylinders arranged in a V configuration, you have a "3.0 liter V-6".
   

• Generally, the displacement tells you something about how much power an engine has. A cylinder that displaces half a liter can hold twice as much fuel/air mixture as a cylinder that displaces a quarter of a liter, and therefore you would expect about twice as much power from the larger cylinder (if everything else is equal). So a 2.0 liter engine is roughly half as powerful as a 4.0 liter engine. You can get more displacement either by increasing the number of cylinders or by making the combustion chambers of all the cylinders bigger (or both).
   

• Connecting Rod
  The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.
   

• Crank Shaft
  The crank shaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.
   

• Sump
  The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).