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Motorcycle Engines



Motorcycle engines work the same way that car engines do. They consist of pistons, a cylinder block and a head, which contains the valve train. The pistons move up and down in the cylinder block, driven by explosions of a fuel-air mixture that has been ignited by a spark. Valves open and close to allow the fuel-air mixture to enter the combustionchamber. As the pistons move up and down, they turn a crankshaft, which transforms the energy from the pistons into rotary motion. The rotational force of the crankshaft is transmitted, via the transmission, to the rear wheel of the motorcycle.




Inside a typical car engine


Motorcycle engines are generally classified by one of three characteristics: the number of cylinders theypossess, the capacity of their combustion chambers or the number of strokes in their power cycles.


Cylinders
Motorcycle engines can have between one and six cylinders. For years, the V-twin design was the engine of choice for motorcycle engineers in America, Europe and Japan. The V-twin gets its name from the fact that the two cylinders form a V shape, such as the classic Harley-Davidson V-twinshown below. Notice the 45-degree angle in the Harley-Davidson V-twin -- other manufacturers may vary this angle to reduce vibration.










|[pic] |
|Photo courtesy Harley-Davidson Motor Company |
|The Revolution, a Harley-Davidson V-twin engine|



The V-twin is just one way to accommodate two cylinders. When the cylinders are oriented so that the pistons oppose each other, the result is an opposed-twin design. Parallel-twin engines have their pistons placed side by side in an upright position.


Today, the most popular design is the four-cylinder, which runs more smoothly and at higher revolutionsper minute (rpm) than a comparable twin. The four cylinders can be placed in a row, or they can be arranged in a V-shape configuration, with two cylinders on each side of the V.

















Capacity



The size of the combustion chamber in a motorcycle engine is directly related to its power output. The upper limit is about 1500 cubic centimeters (cc), while the lowerlimit is about 50 cc. The latter engines are usually found on small motorcycles (mopeds) that offer 100-miles-to-the-gallon fuel economy but only reach top speeds of 30 to 35 miles per hour.





2-stroke engine power stroke

[pic]
In one 2-stroke cycle, the crankshaft does 1 revolution. In that 1 revolution how many strokes does the piston do? 2 strokes. Out of those 2 strokes how manyactually produce power? In a 2-stroke cycle, only 1 stroke delivers energy to the crankshaft.




Two-stroke cycle

The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by completing the same four processes (intake, compression, power, exhaust) in only two strokes of the piston rather than four. This is accomplished by using the space below thepiston for air intake and compression, thus allowing the chamber above the piston to be used for just the power and exhaust strokes. This cause there to be a power stroke for every revolution of the crank, instead of every second revolution as in a four-stroke engine. For this reason, two-stroke engines provide high specific power, so they are valued for use in portable, lightweight applications.On the other hand large two stroke diesels have been in use in industry (i.e. locomotive engines) since the early 20th century.


Applications


The smallest gasoline engines are usually two-strokes. They are popular due to their simple design (and therefore, low cost) and very high power-to-weight ratios. The biggest disadvantage is that the engine lubricant is almost always mixed in...