Bike: In-line 2 / Parallel-Twin / Inline-Twin / Vertical-Twin

Wednesday, 27 January 2016

In-line 2 / Parallel-Twin / Inline-Twin / Vertical-Twin

A straight-twin engine, also known as straight-two, inline-twin, vertical-twin, or parallel-twin is a two-cylinder piston engine which has its cylinders arranged side by side and its pistons connected to a common crankshaft. Compared to V-twins and flat-twins, straight-twins are more compact, simpler, and usually cheaper to make, but may generate more vibration during operation.

Kawasaki ER-6F

Kawasaki ER-6F inline 2, 650cc

Different crankshaft angles are used in four-stroke straight-twins to achieve different characteristics of firing intervals and engine balance, affecting vibrations and power delivery. The traditional British parallel twin (1937 onwards) had 360° crankshafts, while some larger Japanese twins of the 1960s adopted the 180° crankshaft. In the 1990s, new engines appeared with a 270° crankshaft.

Yamaha MT-07

Yamaha MT-07 inline 2 689cc

Straight-twins have the advantage of being more compact, relatively simple, and cheaper to make in comparison to V- or flat-twins. They may be prone to vibration, either because of the irregular firing interval present in 180° crank engines or the large encountered reciprocating mass in 360° crank engines. Inline-twins also suffer further from torsional torque reactions and vibration.