Honda 90° V-twin
A V-twin is a two cylinder internal combustion engine where the cylinders are arranged in a V configuration.
This arrangement is common on motorcycles, the engine can be mounted in transversal position like on Harley-Davidsons, Ducatis and many recent Japanese motorcycles. The longitudinal V-twin as seen on Moto-Guzzis[?] and some Hondas is less common. This position is well adapted to its transmission shafting, but has the disadvantage of causing a torque reaction that tend to lean the motorcycle on the side.
The most obvious configuration for a V-twin is a 90° angle, but others angle can be seen like the 45° Harley-Davidson, the 75° Suzuki and the 60° Aprilia.
The 90° V-twin
A 90° V-twin can achieve perfect primary balance but has some secondary imbalance. The 90° V-twin should be viewed as an alternative to the flat-twin configuration. The flat-twin is perfectly balanced.
Harley-Davidson 45° V-twin
The 45° Harley-Davidson V-twin
The cylinders of the classic Harley-Davidson V-twin are arranged at a 45° angle. The crankshaft has a single pin, and both pistons are connected to this pin through their connecting rods. This design causes the pistons not to fire at even intervals.
The V-twin runs like this: The first piston fires. Then, the other piston fires at 315 degrees into the stroke. There is a 405-degree gap until ... the first piston fires again. This give the Harley-Davidson V-twin it's unique pop-pop...pop-pop...pop-pop sound.