V-образный двухцилиндровый двигатель

Piston engine with two cylinders in "V" configuration
the two cylinder V engine

A V twin engine, also called a V2 engine, is a two cylinder piston engine where the cylinders are arranged in a V configuration and share a common crankshaft. The V twin is widely associated with motorcycles, primarily installed longitudinally, though also transversely. They are also used in a variety of other land, air, and marine vehicles, as well as industrial applications. The V twin design dates back to the late 1880s.

Most V twin engines have a single crankpin, which is shared by both connecting rods. The connecting rods may sit side by side with offset cylinders, or have fork and blade connecting rods which avoids the twisting forces caused by having offset cylinders. Some notable exceptions include a 180° crank pin offset used by the 1935 Moto Guzzi 500cc, a dual crankpin configuration used by the 1983 Honda Shadow 750, and the 75° crank pin offset (45° offset in the United States) used by the 1987 Suzuki VX 800.

Although any 'V angle' (the angle between the two banks of cylinders) between zero and 180 degrees is theoretically possible for a V twin engine, in practice angles smaller than 40 degrees are rarely used. The most common V angle for a V twin engine is 90 degrees, which can achieve a perfect primary balance (if the correct counterweight is used) like most Ducatis, most Moto Guzzis, the Honda RC51, Suzuki TL1000S and TL1000R. However, this arrangement results in an uneven firing order, with the second cylinder firing 270 degrees after the first cylinder, then a 450 degrees interval until the first cylinder fires again. 90 degree engines are sometimes called L twin (like the "L" in TL1000R or TL1000S) rather than V twin. The alternating longer and shorter gaps between firings produce a characteristic V twin alternating engine noise "phutphut phutphut phutphut phutphut". When a V angle of less than 90 degrees is used, perfect primary balance can only be achieved if offset crankpins are used. If not, balance shafts are usually required to reduce the vibration. and the 1940–1948 Zündapp KS 750 (170 degrees).

As per other motor vehicles, the terms longitudinal engine and transverse engine are most often used to refer to the crankshaft orientation relative to the frame. However, some companies use the opposite terminology, stating that a "transverse" V twin engine has the cylinders mounted on each side of the motorcycle (therefore with the crankshaft running in line with the frame) and that a "longitudinal" V twin engine has the cylinders at the front and rear. The latter terminology is used by the Italian manufacturer Moto Guzzi. To avoid such ambiguity, some people use descriptions of "transverse crankshaft engine", "longitudinal crankshaft engine", or "transversely mounted cylinders".

The most common arrangement is to mount the engine with the crankshaft oriented transversely to the frame. The advantage of this mounting is that the width of the motorcycle can be smaller than a longitudinally mounted V twin. A disadvantage of this configuration for air cooled engines is that the two cylinders receive different air flows and cooling of the rear cylinder tends to be restricted (although the uneven cooling isn't as pronounced as a parallel twin engine, where the inner faces of the cylinders are not exposed to any airflow). Some transverse V twins use a single carburettor in the middle of the V angle to feed both cylinders. While this avoids the need for two carburettors, it creates further cooling problems for the rear cylinder by placing its hot exhaust port and pipe at the back of the cylinder, where it may be exposed to less cooling airflow. Transverse V twin engines have been used by Harley Davidson, Ducati and many recent Japanese motorcycles, such as the Suzuki SV650. Some Ducati V twin engines have been marketed as "L twin" engines, due to the front cylinder being vertical and the rear cylinder being horizontal, thus forming an "L" shape.

A less common arrangement is to mount the engine longitudinally. An advantage of this arrangement is that both cylinder heads can protrude into the air stream, so they can each receive the same amount of cooling (for air cooled engines). Also, the transmission being located behind the engine is easier to fit within a typical motorcycle frame and, for shaft drive motorcycles, a 90° bevel gear is not needed at the start of the driveshaft. As per all longitudinal engines, a disadvantage is 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. Longitudinal V twin engines have been used by the Honda CX series and several Moto Guzzi motorcycles.

Most cars are powered by engines with three or more cylinders, however several small cars have been produced with V twin engines particularly during the period from 1912 to 1920 when cyclecars were made by many companies (due to a favourable tax position). Almost all of these used proprietary engines, either adapting the larger motorcycle engines used for sidecar work (large singles or V twins), or using engines specifically made for cyclecars such as those made by J. A. Prestwich Industries ('J. A. P.' engines) or F. E. Baker Ltd ('Precision' engines). In 1912, Humber produced a light car called the Humberette with a Humber made V twin side valve engine of 998cc. The engine had a directly attached clutch, 3 speed gearbox and prop shaft output to a rear differential. A water cooled version of this engine was made available in 1914, but WW1 ended Humberette production in 1915. From 1911 to 1939, various Morgan 3 wheelers three wheeled cyclecar models were powered by V twin engines. Production of three wheeler models then resumed with the 2012–present Morgan 3 Wheeler. Also in the United Kingdom, Birmingham Small Arms Company (BSA) produced several cars powered by their V twin motorcycle engines. These were produced from 1921 to 1926 (four wheel models) and 1929–1936 (three wheel and four wheel models). Several manufacturers have produced models inspired by the original Morgan three wheeled car, such as the 1978–present Triking Cyclecar (using a Moto Guzzi engine), the 2006–present Ace Cycle Car (using a Harley Davidson engine) and the 1990–present JZR Trikes kit car (using engines from several manufacturers). Mazda's first car, the 1960–1966 Mazda R360 rear engined kei car, was powered by the Mazda V twin engine. The 1961–1962 Mazda B360 front engined light commercial vehicle used a version of this engine.

Various V twin engines have been produced for industrial uses such as pressure washers, lawn and garden tractors, tillers, generators and water pumps. The engines are usually air cooled with a 90° V angle. Depending on the application, the engine's orientation can have either a horizontal or vertical crankshaft. Manufacturers of commercial V twin engines include Briggs & Stratton with its Vanguard, Professional and Intek V twin series, Honda with its V twin series engines, Kawasaki with its FD, FH, FR, FS, and FX series, Subaru with its EH series, Tecumseh with its OV691EA and TVT691 engines, and Kohler.