V-twin
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A V-twin is a two cylinder internal combustion engine where the cylinders are arranged in a V configuration.
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[edit] Configurations
[edit] "True V-twin" vs V-2
A common misconception is that V-twin means a V-2 in which the two cylinders share a crank pin and therefore that V-2 engines which have separate crank pins for each cylinder would not qualify as V-twin engines. There is no evidence to support this and the 1983 Honda Shadow 750 is known as being the first V-twin with an offset-dual-pin crankshaft.[1]
[edit] V angles
The most obvious configuration for a V-twin is a 90°, in which counterweighting can balance the engine, in odd-firing 90 degree Vees. This is seen in the Moto Guzzi, Ducati and Suzuki SV650, but other angles can be seen like the 45° of the classic Harley-Davidson engine, the 75° Suzuki, the 52° Honda, the 80° Honda CX-500, the 47° Vincent, the 42° Indian, the 60° Aprilia, the 45° S&S, and the 56.25° S&S X-Wedge.
The signature Ducati engine, a transverse 90° twin with the front cylinder approximately parallel to the ground and the rear cylinder vertical, is sometimes referred to as an "L" twin.
[edit] Orientations
The terms longitudinal engine and transverse engine are used to refer to the crankshaft orientation. A common mistake with V-2 engines is to refer to the cylinder orientation.[2] However referring to the crankshaft gives a correct method to engine orientations as it gives the same orientation for all V-engine types like V-2, V-4 (which would be difficult to describe with cylinder orientation) and V-8.
[edit] Transverse mounting
Both two-cylinder V engines are common on motorcycles. The engine can be mounted in transverse position like on Harley-Davidsons, Ducatis and many recent Japanese motorcycles. This transverse position gives the motorcycle a reduced frontal area. The main disadvantage of this configuration is that the rear cylinder and the front cylinder will receive different air-flows making air cooling somewhat problematic especially for the rear cylinder.
[edit] Longitudinal mounting
The longitudinal two-cylinder V as seen on Moto-Guzzis and some Hondas is less common. This position is well adapted to transmission shafting. When used in motorcycles, this approach has the slight disadvantage of causing a torque reaction that tends to lean the motorcycle slightly to one side as the angular rate of the crankshaft increases or decreases. The faster the change, the larger the torque it produces. However, many motorcycle manufacturers have corrected for torque reaction by rotating the transmission input shafts and/or the balance and drive shafts opposite that of the crankshaft so that there is approximately equal mass turning clockwise and counterclockwise at any time, thereby physically canceling the effect.
[edit] Non-V twin configurations
[edit] Flat twin
The flat twin, or boxer configuration, has a longitudinal crankshaft with the cylinders protruding horizontally from either side of the engine. BMW is the best-known manufacturer of this configuration, which has two advantages: the cylinders are squarely in the airstream and run cooler; and in the event of an accident the cylinders will help protect the rider. Disadvantages of this design are the torque reaction mentioned above in the section on longitudinal mounting, and the engine must be mounted higher in the frame to keep the cylinders from scraping the road in sharp curves.
According to the American Motorcyclist Association's Motorcycle Hall of Fame Museum, regarding the World-War-II-vintage Harley-Davidson XA, which has an opposed twin engine — "Mechanically, the large cooling fins stuck straight out in the breeze, reportedly keeping the XA’s oil temperature 100 degrees cooler than a standard Harley 45."[3] The latter was a transversely mounted V-twin, in which the airstream cannot reach the rear cylinder as efficiently as on a longitudinally mounted flat twin.
Douglas Motorcycles made a flat-twin with fore-and-aft cylinders, which allowed the engine to be mounted lower in the frame. The disadvantage was that the rear cylinder tended to overheat. Currently there are no motorcycles with this configuration in mass production.
[edit] Vertical twin
The vertical twin or parallel twin is another logical alternative to the V-twin. It was made famous by such British motorcycles as Triumph, Ariel, AJS, BSA, Matchless, Norton and Royal Enfield. The parallel twin has also been used by BMW , Benelli, Honda, Kawasaki, Laverda, Suzuki, and Yamaha.
[edit] See also
[edit] References
- ^ Honda: 1983 Shadow 750. Retrieved on 2008-05-20.
- ^ Heritage/History: Design/Technology. BMW Motorcycles.
- ^ Classic Bikes: 1942 Harley-Davidson XA. Motorcycle Hall of Fame Museum. Retrieved on 2008-01-25.
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