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A V-twin is a two cylinder internal combustion engine where the cylinders are arranged in a V configuration.

Contents 1 Configurations 1.1 True V-twin vs V-2 1.2 V angles 2 Orientations 2.1 Transverse mounting 2.2 Longitudinal mounting 3 Non-V twin configurations 3.1 Flat twin 3.2 Vertical twin 4 See also

In a true V-twin engine, for example Harley Davidson engines, the two cylinders share a single crank pin (also known as a journal) on the crankshaft, therefore the "twin" nomenclature. Two cylinder, V shaped engines with separate crank pins for each cylinder are more properly called "V-2" engines, however, proper identification of V-2 engines is uncommon. They are frequently referred to as V-twin engines, too, although this is technically incorrect.^{[citation needed]}

For animations of a V Twin engine:Harley Animation

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 and Ducati, 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, and the 60° Aprilia.

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.

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 (as mentioned on BMW's web site). 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.

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.

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. 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.

On motorcycles, flat twins can be positioned either with the crankshaft positioned longitudinally, as in the BMW twins, or tranversely, as in the Douglas. The cylinders of a longitudinally mounted flat twin motorcycle engine protrude sideways into the air stream.

The flat-twin configuration is one logical alternative to the longitudinal V-twin motorcycle engine. The flat-twin has better overall engine balance but the longitudinally mounted version is wider in profile. The latter flat-twin must be mounted high on the motorcycle to avoid cylinder heads touching the ground in a sharp curve. On the other hand a V-twin and traversely mounted flat twin could be mounted lower and could result in a lower center of gravity for the whole motorcycle.

Engine cooling is an advantage of the longitudinally mounted flat twin. 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."[1] 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.

The vertical twin or parallel twin is another logical alternative to the V-twin. It was made famous by such British motorcycles as Triumph, BSA, Enfield, and Matchless.

• Engine balance
• Flat-twin

v • d • e Piston engine configurations
Straight	Single · 2 · 3 · 4 · 5 · 6 · 8 · 9 · 10 · 12 · 14
Flat	2 · 4 · 6 · 8 · 10 · 12 · 16
V	2 · 4 · 5 · 6 · 8 · 10 · 12 · 16 · 20 · 24
W	8 · 12 · 16 · 18
Other inline	H · U · Square four · VR · Opposed · X
Other	Hemi · Radial · Rotary · Pistonless (Wankel)

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