Questions
What is the difference between two-stroke and four-stroke?
The difference between two-stroke and four-stroke engines comes down to how often each cylinder fires: a two-stroke fires once every revolution, a four-stroke once every other revolution.
A four-stroke engine completes four separate piston movements - intake, compression, power and exhaust - over two full crankshaft revolutions, firing once every other turn. A two-stroke compresses that same cycle into a single revolution, firing every time the piston goes up, which makes it lighter for its capacity and quicker to rev. Two-strokes were common on smaller road bikes and off-road machines for decades because of that light, revvy character, but tightening emissions rules have pushed most modern road bikes toward four-stroke engines, which burn fuel more completely and need no oil mixed into the petrol. Two-strokes still turn up in some off-road and competition machines, where the weight saving and instant power delivery matter more than emissions.
Whichever kind of engine is under the tank, our motorbike gifts for men range turns the bike itself into art from a photo. See also what does cc mean on a motorbike? for the other basic engine question.
Written by Craig Fearn, Throttlefolio.
Transmissions
Questions, answered
Why do two-strokes need oil mixed with the fuel?+
There is no separate oil sump - the mixed-in oil is what lubricates the piston and bearings as the fuel-oil mix passes through the engine.
Are two-stroke road bikes still made?+
Very few - emissions rules have pushed almost all modern road bikes to four-stroke engines, though two-strokes persist in some off-road and competition machines.
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