A single-cylinder engine, sometimes called a thumper, is a piston engine with one cylinder. This engine is often used for , motor scooters, motorized bicycles, , all-terrain vehicles, radio control, and garden machinery (such as , , , and ). Single-cylinder engines are made both as 4-strokes and 2-strokes.
Drawbacks of single-cylinder engines include a more pulsating power delivery through each cycle and higher levels of vibration. The uneven power delivery means that often a single-cylinder engine requires a heavier flywheel than a comparable multi-cylinder engine, resulting in relatively slower changes in engine speed. To reduce the vibration level, they often make greater use of than multi-cylinder engines, as well as more extreme methods such as a dummy connecting rod (for example the Ducati Supermono).Methods of Balancing Single Cylinder Engines. Joseph R. Harkness. SAE Transactions. Vol. 77, Section 3: Papers 680436–680591 (1968), pp. 2329-2338 Suzuki's Supermono Engine Design. A second con-rod without a piston. Ben Purvis. April 26, 2019 These balancing devices can reduce the benefits of single-cylinder engines regarding lower weight and complexity.
Most single-cylinder engines used in motor vehicles are fueled by petrol (and use a four-stroke cycle), however diesel fuel single-cylinder engines are also used in stationary applications (such as the Lombardini 3LD and 15LD).
A variation known as the split-single makes use of two pistons which share a single combustion chamber.
Single-cylinder engines remain the most common engine layout in and low-powered . The Honda Super Cub (the motor vehicle with the highest overall sales since its introduction in 1958) uses a four-stroke single-cylinder engine. There are also several single-cylinder (such as the KTM 690 Duke R), dual-sport motorcycles (such as the BMW G650GS) and the classic-styled Royal Enfield 500 Bullet.
The Moto3 class in the MotoGP World Championship have used four-stroke single-cylinder engines since the class replaced two-strokes in 2012.
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