The history of the motorcycle engine evolution is a riveting tale. Engine design has transformed beyond recognition from the primitive steam-powered safety bikes of the 19th century to the four-stroke engine of modern Harley-Davidsons.
Riding at Full Steam
The 19th century was the era of steam power, so it should come as no surprise that the first motorcycles had steam engines. In 1867, the American Sylvester Howard Roper created one of the earliest known motorcycle prototypes — the Roper Steam Velocipede. As the name suggests, it was little more than a steam-powered bicycle.
Two Strokes Are Better Than One
In 1908, the Yorkshireman Alfred Angas Scott invented the first water-cooled motorcycle with a two-stroke combustion engine, which itself had been patented back in 1881 by the Scottish engineer Dugald Clerk.
Internal combustion engines work by burning fuel (usually gasoline) inside a combustion chamber. The combustion chamber is inside a cylinder sealed by cylinder heads. Inside the cylinder, a piston moves up and down when the engine is running.
While the piston moves, tiny valves open and close to let fuel and air in and expel exhaust gasses. Modern bikes usually have four valves per cylinder.
As the piston rises, it pulls in air and fuel through an intake valve and compresses the mixture in the combustion chamber. When the mixture reaches the top of the chamber, a spark plug ignites the mixture and pushes the piston back down. At the same time, exhaust gasses exit through an exhaust valve.
Two-stroke engines convert fuel into motion in one up-and-down movement (two strokes) of the piston. These engines are more polluting than their four-stroke counterparts, so today we mainly use them on lighter applications like generators, lawnmowers, and go-karts. Still, some motorcycle producers like KTM continue to develop two-stroke engine bikes.
The Otto Engine
Around a decade earlier, in 1885, the Germans Wilhelm Maybach and Gottlieb Daimler equipped a safety bicycle with a four-stroke cylinder combustion engine, creating the first gas engine bicycle — the Daimler Petroleum Reitwagen.
Engineer Nikolaus August Otto famously invented the four-stroke combustion engine in 1876. These types of engines eventually became known as “Otto engines.”
Unlike two-stroke engines, four-stroke motors convert fuel into energy in four piston strokes:
- The first downward stroke lets the air and fuel mixture in.
- On the second stroke, the upward movement compresses the mixture, which ignites as the piston reaches the top.
- After the combustion, the piston moves downward in the third stroke.
- On the fourth and final stroke, the piston goes up again, expelling the exhaust gasses.
The four-stroke engine catapulted the mass production of motorcycles worldwide, leading to beloved models like Harley-Davidsons, ultra-fast Japanese bikes, custom bikes with the same thickness and diameter of the front and rear wheel, and more.
The Future Is Electric
Electric-powered motors are the next step in motorcycle engine evolution. While there have been attempts to use electricity as a power source since 1869, it was not until the mid-1990s that Peugeot launched the first mass-produced electric motor scooter: the Scoot’Elec. With the increasing demand for green energy, and the demographics of motorcycle owners getting younger and younger, it’s likely there will be more electric-powered motorcycles in the near future.
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