Flat-twin engine
The Australian lawnmower manufacturer Victa also produced a flat-twin engine push mower from August 1975 to 1980 dubbed the ‘Twin 500’, and later the ‘Supreme’.
They are very sought after as only small numbers were produced, most likely due to ignition- and fuel-related problems in early models.
In the Supreme (the later model) all these problems were fixed with a rear-domed piston, crankcase mixers and refined ignition system[citation needed].
The equal and opposite forces in a boxer-twin engine do however generate a rocking couple, due to the offset distance between the pistons along the crankshaft.
[13] The first flat-twin motorcycle engine was built in 1905 by the Light Motors Company in the United Kingdom.
Originally named the Fée (renamed "Fairy" soon after its introduction),[15] it was designed as a "bicycle engine system" which transmitted power to a pulley on the rear wheel via a chain.
[1]: 218–219 Later in 1907, Douglas changed the drivetrain from the chain and pulley design to a belt-drive system driven directly from the engine.
[24] A side benefit is that the cylinders provide protection to the rider in the event of a collision or fall, and keeps their feet warm in cold weather.
[13][1]: 27 Longitudinal mounting also means that the torque reaction will twist the motorcycle to one side (such as on sharp acceleration/deceleration or when opening the throttle in neutral) instead of shifting the weight balance between the front and rear wheels.
However, many modern motorcycles reduce this effect by rotating flywheels or alternators in the opposite direction to that of the crankshaft.
BMW has a long history of flat-twin engine motorcycles,[1]: 26–32 [28] as do Ural (Russia) and Dnepr (Ukraine).
In 1902, the Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine built on a farm by a hobbyist inventor.
[29][30][31] This engine used the unusual design of a single shared crank pin and double acting pistons.
[32][33] In 1908, the French company Dutheil-Chalmers began production of flat-twin aircraft engines, which used two counter-rotating crankshafts.
In the 1940s, they were largely replaced by straight-twin two-stroke engines, which were easier to start and no longer had excessive amounts of vibration.
