The one item you need for a bike to be considered a motorcycle is the motor or engine. Walk around any area where you can see bikes lined up and you will see engines of all shapes and sizes. Seems lately the fad is to have a bigger one...

than the next person. Sounds like something us men have been trying to brag about since the beginning of time. If it is the Sport bikes you will see 900, 1000, 1300, and so on. These numbers represent the size of the engine in CC’s  or cubic centimeters. On the American V twins you will see 88, 96, 124, and so on. These numbers represent the size of the engine in CI or cubic inches. The difference is CC is metric and CI is Standard American measurement. What these engines have in common is they are all four- stroke engines.

Engines have been around for well over a hundred years. Since the late 1800’s there has been some sort of internal combustion engine built. It was Nicolaus Otto who in 1876 designed, invented, and built the first internal combustion gas fueled four- stroke engine. Coincidentally enough, this first true gas fueled four- stroke engine was built into a motorcycle. Since then as you can imagine there have been vast design changes and improvements that have allowed us to get more power with better efficiency and reliability. However the same principals of the four- stroke engine exists.

Why is it called the four- stroke engine? You ask? Well it is named that simply because of the way the engine works. It utilizes four strokes of the piston in a cylinder to complete its task of making power. First there is the intake stroke. The piston travels down in the cylinder while the intake valve in the cylinder head is open to draw in fresh oxygenated air and fuel. Then there is the compression stroke, in which the piston travels in an upward direction in the cylinder with all the valves closed. Giving nowhere for the air and fuel to go, this action compresses this air fuel mixture causing it to rise in temperature. The fuel then atomizes and the atoms that make up the air fuel mixture move more rapidly allowing for better ignition. The spark plug is then fired and this ignites the mixture. The ignition creates an explosion in the cylinder causing the piston to be driven in a downward direction with great force and power, thus creating the power stroke. The piston then travels back up the cylinder and the exhaust valve is opened allowing the burned air fuel mixture to escape causing what we call the exhaust stroke.

There are many other components performing different functions that allow for the operation of the engine. We will get into explaining the rest of the operating components and systems at a later time. But it is the four strokes that is the heart of the operation. These four strokes allow us a way to get air, fuel, and ignition together in an environment capable of capturing the effects of combustion and turning it into usable power and torque. So remember there are different strokes for different folks but it is the four strokes that makes your motor hum.