# Cylinder The space in which a piston travels. The piston is seated inside of the cylinder and moves up and down. # Intake Valve A valve that is opened at the correct time to allow the fuel air mixture to enter into the cylinder. Generally the intake valve is opened just before the piston reaches top dead center, meaning that the piston is at the top of the cylinder. # Exhaust Valve A valve that is opened to allow the exhaust fumes from combustion to exit the cylinder. # Piston The circular device that slides up and down the cylinder, allowing it to compress the fuel air mixture, or to push out exhaust gasses. # Spark Plug What initiates the combustion. By creating a spark using electricity, the spark plug ignites the fuel air mixture and forces the piston down to the bottom of the cylinder. # Connecting Rod What connects the piston to the crankshaft. As the piston moves up and down, the connecting rod pushes and rotates the crankshaft. # Crankshaft The crankshaft is what converts the linear motion of the piston into rotational motion. # Crankcase The crankcase is what houses the entire crankshaft. Can be thought of as the main component of the engine, where all of the work is done.