Motors are not engines - some engine info here

This depicts a "two stroke" engine, typically found in small gas-powered devices:  mopeds, chainsaws....


http://science.howstuffworks.com/transport/engines-equipment/two-stroke1.htm

http://science.howstuffworks.com/transport/engines-equipment/two-stroke2.htm

The more complicated case of the 4-stroke engine:

http://auto.howstuffworks.com/engine1.htm

http://auto.howstuffworks.com/engine2.htm

More info, FYI:

http://auto.howstuffworks.com/engine4.htm