DKW RT 250 (1952–1953) motorcycle engine

A single-cylinder engine, sometimes called a thumper, is a piston engine with one cylinder. This engine is often used for motorcycles, motor scooters, go-karts, all-terrain vehicles, radio-controlled vehicles, portable tools and garden machinery (such as lawnmowers, cultivators, and string trimmers). Single-cylinder engines are made both as 4-strokes and 2-strokes.


Villiers engine in a 1959 Bond Minicar

Compared with multi-cylinder engines, single-cylinder engines are usually simpler and compact.[1] Due to the greater potential for airflow around all sides of the cylinder, air cooling is often more effective for single cylinder engines than multi-cylinder engines. This reduces the weight and complexity of air-cooled single-cylinder engines, compared with liquid-cooled engines.

Drawbacks of single-cylinder engines include a more pulsating power delivery through each cycle and higher levels of vibration.[2] 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 balance shafts than multi-cylinder engines,[3] as well as more extreme methods such as a dummy connecting rod (for example the Ducati Supermono).[4][5] 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),[6][7][8] however diesel 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.


Yamaha SRX600 (1985–1997) motorcycle engine

Early motorcycles, automobiles and other applications such as marine engines all tended to be single-cylinder. The configuration is almost exclusively used in portable tools, along with garden machinery such as lawn mowers.[9] Single cylinder engines also remain in widespread use in motorcycles, motor scooters, go-karts, auto rickshaws, and radio-controlled models. From 1921 to 1960, the Lanz Bulldog tractor used a large horizontally-mounted single cylinder two-stroke engine.[10] However they are rarely used in modern automobiles and tractors, due to developments in engine technology.

Single cylinder engines remain the most common engine layout in motor scooters and low-powered motorcycles. The Honda Super Cub (the motor vehicle with the highest overall sales since its introduction in 1958) uses a 49 cc (3.0 cu in) four-stroke single-cylinder engine. There are also several single-cylinder sportbikes (such as the KTM 690 Duke R), dual-sport motorcycles (such as the BMW G650GS) and the classic-styled Royal Enfield 500 Bullet.[11][12]

The Moto3 class in the MotoGP World Championship have used four-stroke 250 cc (15.3 cu in) single cylinder engines since the class replaced 125 cc (7.6 cu in) two-strokes in 2012.

Other single-cylinder engines

Engines of other sorts, like the beam engine and certain types of Stirling engine, operate using one cylinder and thus can also be considered single-cylinder engines.


  1. ^ "Single Cylinder Engines". TheBikeMarket. Archived from the original on 2019-12-17.
  2. ^ "How to Balancing a Single Cylinder Engine Crankshaft and Piston/Connecting Rod Assembly and Flywheel to Reduce Dangerous Vibration". Retrieved 10 July 2019.
  3. ^ "Engine Science: The Balancing Act of Single Cylinder Engines". Retrieved 10 July 2019.
  4. ^ Methods of Balancing Single Cylinder Engines. Joseph R. Harkness. SAE Transactions. Vol. 77, Section 3: Papers 680436–680591 (1968), pp. 2329-2338
  5. ^ Suzuki's Supermono Engine Design. A second con-rod without a piston. Ben Purvis. April 26, 2019
  6. ^ "5 of the funkiest single-cylinder street bikes". 5 March 2009. Retrieved 7 July 2019.
  7. ^ "The Single Life: 6 of the best thumpers". Retrieved 7 July 2019.
  8. ^ "The 16 Best Retro Motorcycles Make Bikes Great, Again". 9 August 2016. Retrieved 7 July 2019.
  9. ^ "How Car Engines Work". 5 April 2000. Retrieved 10 July 2019.
  10. ^ "The Lanz Bulldog". December 1988. Retrieved 10 July 2019.
  11. ^ "690 Duke: The essence of motorcycling". Archived from the original on 2012-06-12. Retrieved 2012-06-01.
  12. ^ David Blasco. "Royal Enfield Motorcycles". Archived from the original on 2011-12-07. Retrieved 2011-12-06.