The two-stroke engine cycle differs from the more common four-stroke
cycle by having only two strokes (linear movements of the
piston), although the same four operations (intake, compression,
power, exhaust) still occur. Thus, there is a power stroke
per piston for every engine revolution, instead of every second
two strokes first, intake
and compression, second,
combustion and exhaust.
Two-stroke engines are light, mechanically simple and produce
more power than a similar size four stroke when running well.
The down sides of a two-stroke are: They are oily and dirty,
require regular maintenance, and power is only available in
a narrow rpm band, often referred to as the power band.
Two stroke sportbikes like the Aprilia
RS250 are well known for their acute handling, lightweight,
and narrow powerband, unfortunately they are no longer produced.
Four-stroke engines are by far the most
common type of engines found in modern motorcycles. The four-stroke
engine operates on the exact same principle as regular car
engines except on a smaller scale. Four-strokes are cleaner,
more reliable and power comes across a much wider range of
rpm than two-strokes.
Engines come in a variety of cylinder configurations and numbers.
Some general rules which most engines live by are: More cylinders
usually allows for a higher maximum rpm. Less cylinders provide
more torque at
low rpm. And vibrations tend to decrease with more cylinders.
One cylinder, or single cylinder engines as they are
commonly known, are just that. One cylinder, usually positioned
vertically with a single spark plug attached to the top.
Two cylinder engines, or twins,
are one of the most popular types of motorcycle engine. V-twins
are the most common 2 cylinder engines, the cylinders are
positioned in a 'V' configuration with both cylinders pointing
upwards, V-twin engines power all Harley-Davidson bikes and
many sportbikes with 'character'.
V-twin engine BMW
L-twin engines power some Ducati motorcycles, this is essentially
a V-twin with one cylinder pointing horizontally forward.
Parallel twins exist where the cylinders are positioned parallel
to one another.
BMW produces boxer twin (otherwise known as flat twin) engines.
In a boxer twin engine the cylinders are opposed to one another
and move in a manner similar to a boxers fists.
Three cylinder engines, or triples are less common.
However, companys such as Triumph and Benelli have produced
several triple engines. Triumph has cornered the market in
triples and their newest sportsbike the Daytona
675 Triple is one of the most desirable bikes on the market
Four cylinder engines are similar to small car engines,
the cylinders are normally positioned in an in-line configuration,
where the cylinders are lined up one after another in a line.
V and square twin designs have also been produced.
A less conventional motorcycle engine, comes in the MTT
Y2K Turbine superbike. This bike is fitted with an aircraft
grade jet engine, not a common engine choice for motorcycle
to all motorbikes