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A single-cylinder engine is a basic piston engine configuration of an internal combustion engine. It is often seen on motorcycles, auto rickshaws, motor scooters, mopeds, dirt bikes, go-karts, radio-controlled models, and has many uses in portable tools and garden machinery. Some single-cylinder automobiles and tractors have been produced, but are rare today due to developments in engine technology.
Single-cylinder engines are simple and compact, and will often deliver the maximum power possible within a given envelope. Cooling is simpler than with multiple cylinders, potentially saving further weight, especially if air cooling is used.
All else being equal, a single-cylinder engine requires a flywheel with a greater moment of inertia than a comparable multi-cylinder engine, meaning relatively slower changes in engine speed. In the basic arrangement singles are prone to vibration relative to comparable engines, so they often make greater use of balance shafts than multi-cylinder engines, as well as more extreme methods such as a dummy connecting rod, as on the Ducati Supermono single or the BMW F-series twin. These balancing devices can mitigate the benefits of the single's lower weight and complexity.
A variation known as the split-single makes use of two pistons which share a single combustion chamber.
Pros and cons
Single-cylinder engines are simple and economical in construction. The vibration they generate is acceptable in many applications, while less acceptable in others. Counterbalance shafts and counterweights can be fitted but such complexities tend to counter the previously listed advantages.
Components such as the crankshaft of a single-cylinder engine have to be nearly as strong as that in a multi-cylinder engine of the same capacity per cylinder, meaning that some parts are effectively four times heavier than they need to be for the total displacement of the engine. The single-cylinder engine will almost inevitably develop a lower power-to-weight ratio than a multi-cylinder engine of similar technology. This can be a disadvantage in mobile operations, although it is of little significance in others and in most stationary applications.
Early motorcycles, automobiles and other applications such as marine engines all tended to be single-cylinder. The configuration remains in widespread use in motorcycles, motor scooters, mopeds, dirt bikes, go-karts, auto rickshaws, and radio-controlled modes, and is almost exclusively used in portable tools, along with garden machinery such as lawn mowers. Lanz Bulldog tractors and several copies by the Polish company URSUS featured large horizontally mounted single cylinder engines.
The bestselling motor vehicle of the world, the Honda Super Cub, has a very fuel-efficient 49 cc single-cylinder engine. Almost every scooter on the market recently has a single-cylinder engine, and are commonplace in motorcycles. There are sportbikes like the KTM 690 Duke R which has a 70 hp 690 cc single-cylinder engine, dual-sport motorcycles like the BMW G650GS, scooters like Gilera Fuoco 500 as well as classics like the Royal Enfield 500 Bullet with a long-stroke single-cylinder engine.
- 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
- "Archived copy". Archived from the original on 2012-06-12. Retrieved 2012-06-01.CS1 maint: Archived copy as title (link)
- David Blasco. "Royal Enfield Motorcycles". Royalenfields.com. Archived from the original on 2011-12-07. Retrieved 2011-12-06.