TWIN’S GOOD VI­BRA­TIONS

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

MCN - - THIS WEEK - ByPhil West MCN CON­TRIB­U­TOR

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’

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