Motorcycle Engine Types – Part I
In the more than 100 year history of motorcycle design there have been a dozen or more engine types. But as with most technology, those that didn't meet the tests of cost-effectiveness and customer acceptance have fallen away. Here are some basic facts and a few of the winners.
Except for some scooters and mopeds, motorcycle engines
are of the internal combustion type, and what they combust
is gasoline. Gasoline and air are sucked or injected into a
chamber, called the cylinder, when a round piston on a rod
moves downward. The piston moves part way back up the
cylinder, compressing the gas-air mixture and a spark plug
produces a spark across a small gap between two metal
prongs.
That spark ignites the fuel and, as it burns, the product
gases expand explosively, pushing the piston back down. The
force is transferred via the crankshaft and/or chain or belt
to the rear wheel and the bike moves forward.
How many cylinders there are -- and how they're arranged --
determines the basic engine types.
Single Cylinder
Just what the name says, this type has a single chamber with one piston. Used almost exclusively in off-road bikes, they produce loads of torque at lower rpm (revolutions per minute). Unfortunately, since there's nothing to counter-balance the movement of the single piston, they also produce a lot of vibration. The sound produced is something only a motocross fan could love.
Twin Cylinder
The dual cylinder type comes in a variety of
configurations, but most today are V-shaped - the pistons
are angled at 90 degrees (there are several exceptions).
They produce more power than single cylinder engines, owing
to the greater displacement and amount of fuel combusted.
Displacement is, roughly, the volume of the cylinder above
the piston.
They also tend to vibrate much less because, as the number
of cylinders increases, the more forces in a particular
direction are offset.
Some variations involve putting the cylinders side-by-side
or opposed. The latter is called a 'Boxed' or 'Boxer' design
and they produce good power with low vibration.
Unfortunately, the cylinders protrude out the sides, making
cornering difficult and generating the need to protect the
riders legs against heat. Triumph has used the design off
and on over the years since WWII.
The Triple
Though much less common, this three-cylindered design has
excellent power and vibration characteristics. But the
number of moving parts is much greater and it increases the
number of carburetors or fuel injectors required.
Again showing their interest in less-common engine designs,
Triumph has produced 'triples' and they go like the wind.
One of the advantages of more cylinders is the ability to
produce higher rpm. That produces more power, while weighing
less than four cylinder designs.
When selecting a bike styling, comfort, stability and speed
are all going to be important. But central to any choice is
the engine onboard. Which you choose will be determined, in
part, by the kind of riding you intend to do.
Off-road you'll want lots of torque at low rpm to climb
hills and accelerate quickly through sharp turns. Single or
twin is going to be your preferred type. Standard bikes used
for commuting around town will eliminate the single, and may
even nudge you toward a four cylinder.
Motorcycle Engine Types - Part
II