Motorcycles are complicated machines. They have many fast moving parts that work together to make the motorcycle run.
The two main types of motorcycle engines are two-stroke engines and four-stroke engines. Four-stroke engines run more efficiently, use less fuel and create less pollution than two stroke engines, but they are larger and harder to look after.
Two-stroke engines are made up of these parts:
First, an air and fuel mixture enters the intake port. Then the
piston rises, compressing the mixture.
Next, the spark plug ignites the mixture which creates an explosion in
the engine cylinder. The force of the explosion pushes the piston down,
turning the crank around. Then the crank ultimately turns the wheel.
When the piston goes down, the exhaust exits through the exhaust port and
out the exhaust pipe. This happens over and over again very fast.
Four-stroke engines are made of these parts:
First, the intake valve opens and an air and fuel mixture comes
in. Then the piston rises compressing the mixture. Next, the spark plug
ignites the mixture creating an explosion in the engine cylinder. The
force of the explosion pushes the piston down, turning the crank. Then
the crank ultimately turns the wheel. The crankshaft also turns the
crankshaft which turns the timing chain. The timing chain turns the
camshafts. The camshaft for the exhaust valve turns the lobe, which
pushes on the spring-like stem. This spring-like stem opens the exhaust
valve. Then the piston goes up pushing the exhaust into the exhaust
valve and out the exhaust pipe. Then the piston goes back down, turning
the crank. The crank turns the crankshaft, which turns the timing chain.
The timing chain turns the camshafts. The camshaft for the intake valve
turns the lobe, which pushes the spring-like stem. This spring-like stem
opens the intake valve and the fuel comes in. This happens over and over again very fast.
Different motorcycles have different engine configurations
depending on how big and how fast they are. For example, a motorcycle
designed for speed would probably have a four-stroke engine because it
needs a greater amount of speed. Each cylinder has its own piston crank
and whatever its engine needs to operate. Here are some cylinder
The transmission transmits the power from the engine (the
piston/pistons turning the crankshaft) to the rear wheel. The
transmission is made up of the gearbox, the clutch, and the final drive.
The gearbox is
made of a series of gears in various sizes. When a rider switches gears,
different pairs of gearwheels lock together. In the lowest or slowest
gear, a large wheel and a small wheel lock together. In the highest
or fastest gear, wheels of a similar size lock together.
The clutch connects and disconnects power from the engine to
the gearbox. The clutch must be "switched off" by the rider
pulling on the clutch lever located on the left handlebar. If the power
from the engine is not turned off, the gearwheels in the gearbox will
grind together when the rider switches gears.
The final drive is the part that carries the power from the
gearbox to the rear wheel, by using a chain, a belt or a metal shaft.
The chain is most commonly used, followed by the metal shaft, and finally
The fuel system lets the fuel and air mixture into the engine.
The fuel system is made up of the fuel tank, the fuel line and the
carburetor. The fuel tank holds the fuel, and the fuel line carries the
fuel from the fuel tank to the carburetor. While the fuel comes into the
carburetor, air is also coming in. There are three main types of
All of these carburetors use the Venturi Principle. The venturi in a carburetor is a narrowing of the air passageway that causes an increase in air pressure. The increased pressure creates a vacuum effect that draws fuel into the airstream.
The throttle grip is connected to a cable. When the rider twists
the throttle grip, it pulls the cable, which opens the throttle valve,
allowing more fuel and air mixture into the engine cylinder. The more
mixture the rider lets in the faster the engine goes.
The throttle grip is also connected to a cable. When the rider twists the throttle grip, it pulls the cable, which opens the throttle valve. This increases the vacuum effect, pushing the throttle piston up, and allowing more fuel and air mixture into the engine cylinder. This makes the engine go faster.
The throttle grip is connected to a cable just like the butterfly
controlled carburetor and the vacuum controlled carburetor. But instead
of the cable opening a throttle it opens a throttle piston, which lets
more fuel and air mixture into the engine cylinder. It also increases
the vacuum effect.
The ignition system starts the engine. The battery powers most
motorcycle ignition systems. There are wires that transfer the power
from the battery to the spark plug. These wires run through several
different components of the ignition system.
The Ignition Coil
The ignition coil is a part of the ignition system. The ignition
coil increases the voltage of the wires from 12 volts to more than
20,000 volts. You may want to know how this happens. There are primary and
secondary windings that are made of thick and thin wires that conduct
the electricity. The primary windings are made of about 200 turns of
thick wire around an iron pole, and the secondary windings are made of
about 20,000 turns of thin wire around an iron pole.
The Switching Device
The switching device is also a part of the ignition system. The
crankshaft or camshaft powers the switching device that activates the
ignition coil. Some switching devices have contact points while other
more modern ones use magnetic electronic devices.
The combustion process must occur near the end of the compression
stroke, just before the piston reaches its highest point.
throughout the engine to keep the metal parts moving smoothly and
quietly. The oil gets heated up by all the fast moving parts that create
friction, plus the explosion/explosions in the engine
cylinder/cylinders. When the oil gets to the oil cooler and is cooled by
the air passing by, then it goes back through the engine. In a
two-stroke motorcycle, the engine is lubricated by putting oil with the
fuel. But in a four-stroke engine, the lubrication system is separate
from the fuel. In an air cooled engine, the oil is cooled with the same
cooling system used to the engine. But in water cooled engines, the oil
cooler is separate from the cooling system used to cool the engine.
There are two kinds of cooling systems. The two different kinds are air-cooled and
water-cooled. Water-cooled engines are more efficient than air-cooled
engines, because the air outside can change temperature, so it isn’t
always going to be cool.
Air-cooled engines have cooling fins on the outside of the
engine. These fins allow air to enter the engine and cool it. Air-cooled
engines are probably more common than water-cooled engines.
Water-cooled engines use water to cool. The water is pumped throughout the casing of the engine absorbing the heat. Then the heated water returns to the radiator where the passing air cools the water before it is pumped back throughout the engine.
The brakes stop the motorcycle. There are two brakes. One is on the
back wheel and one is on the front wheel. Normally the rider can activate the
front wheel brake with a lever on the right handlebar, and the back
brake with a pedal near the right footrest. The two main kinds of
brakes are disk brakes and drum brakes. These two types of brakes can either
be hydraulically operated or mechanically operated. Most disk brakes are
hydraulically operated and most drum brakes are mechanically operated.
Disk Brakes and Hydraulic
When the hand brake is
squeezed, brake fluid gets pushed through the brake line by a tiny
piston within the brake cable. This fluid creates pressure in the
calipers squeezing the disk attached to the wheel.
Drum Brakes and Mechanical
Drum brakes work a lot like bicycle brakes. When the rider squeezes the brake lever, a cable gets pulled. That cable causes the shoe to press against a bowl-like drum attached to the wheel hub.
Bruce A., and David D. Edmundson. Motorcycles:
Fundamentals, Service, Repair. Tinley Park: The Goodheart-Willcox
Company, Inc., 1987.
Kerrod, Robin. How•It•Works: Motorcycles. New York: Gloucester Press, 1989.
Phillips, John. Personal interview. 16 January 2005.
Kern, Walter. “How Does a Motorcycle Work?” About. 16 January 2005 <http://motorcycles.about.com/cs/beginners/1/blpart034.htm>.
Copyrighted clip art image of motorcycles in upper left corner of page from "Microsoft Office Online" <http://office.microsoft.com/clip art/default.aspx?lc=en-us&cag=1> (October-March, 2004-2005). Clip art available only to licensed users for non-commercial purposes.
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