TWIN’S GOOD VIBRATIONS

Enfield worked hard to give new 650 the right mix of power, sound and feel

When it comes to engines, not all twins are identical, as Royal Enfield’s eagerly anticipated new 650 proves. Or does it? The Indian-owned firm will launch their all-new, 650cc Interceptor and Continental GT soon but in creating the new engine, Enfield’s British-based development team, led by Simon Warburton, faced a common dilemma associated with parallel twins: what firing order is best? By their very nature, parallel twins have different performance, character, sound and vibration depending on the firing order of their cylinders. If both pistons rise, fire and fall at the same time, it’s a 360-degree firing order (and works and feels much like a big single). If one piston is at the bottom of its stroke with the other at the top, it’s a 180-degree arrangement. The traditional British parallel twin, from the 1937 Speed Twin onwards, had 360-degree crankshafts that gave good torque but greater vibration due to the bigger, less frequent ‘bangs’. They were also more suited to single carbs. By the 1960s, though, most Japanese twins had dual carbs and 180-degree cranks, which gave more power but also tingly ‘secondary’ vibes due to their uneven firing orders.

But since Yamaha’s 1995 TRX850 there’s been an increasingly popular third way. That twin had a 270–degree firing order, which gave more regular bangs than a 180-degree crank but less vibration than a 360. It also had the bonus of sounding and feeling similar to a 90º V-twin. The idea was for the bike to have the soul to take on more exotic machines such as the then-popular Ducati 900SS. The 270-degree crank has proved so successful today it’s used on nearly all parallel twins. So, while Hinckley’s first retro 800 Bonneville back in 2000 was a 360 to mimic the feel and sound of the 1959 original, since 2016 they’ve all been 270s. So too are Yamaha’s MT-07, Kawasaki’s Z650, BMW’s F850GS and Honda’s new Africa Twin. And guess what? The new Royal Enfield is as well. “We experimented with three configurations for the 650 twin and tested them on track,” Warburton told MCN. “We built a 180, 270 and 360 crank but settled on the 270 because it had the right balance of vibrations, power delivery and sound.” Maybe most twins are the same these days, after all.

‘The 270 crank has the right balance of vibes’