Rattlebattle, A 270° crank gives the best possible secondary engine balance for a parallel twin,
(Complex maths which I can't find a reference for at the moment.
https://wikivisually.com/wiki/Yamaha_TR ... crankshaft
"Although the 270° crank concept has been attributed to Australian Phil Irving (of Vincent renown),[7] the TRX was the first[9] production motorcycle to feature this innovation. The 270° crank has an ignition sequence and an engine balance that yields something of the feel of a V-twin. Unlike 180° & 360° parallel-twins, a 270° engine in motion never has both pistons stationary, so its flywheel momentum is continuous.[3] With less vibration than a 360° crank, and a more regular firing pattern than a 180° crank, a 270° crank results in a smoother engine. Any remaining unevenness of the 270° firing interval has been claimed to deliver power to the rear tyre more effectively.[10]
Since the TRX's demise, the 270° layout has been adopted by large parallel-twins in standard and cruiser motorcycles as the concept appears to be an ideal compromise and optimal configuration.[11] Although in recent years no 270° crank in mid or large capacity parallel-twin has been used in any modern-day sportbike.[citation needed] The 2009 Triumph Thunderbird, the 2010 Norton Commando 961, and the Yamaha MT-07 are all 270° designs. The 2016 Honda 1000cc Africa Twin has a 270° parallel-twin,[12] rather than the V-twin of earlier incarnations; and the recent BMW parallel-twin is a 270° design. Whilst the 900cc Triumph Thruxton had a 360° crank, its 2016 successor, the 1200cc Triumph Thruxton adopted the 270° layout. [13] Stuart Wood, Triumph’s Chief Engineer, stated a 270° crank to be ideal for large-capacity parallel twins, as it generates fewer of those irritating high frequency secondary vibrations. [14]
The 2017 KTM 790 Duke is also a 270° parallel twin. KTM's technical head, Jürgen Hager, said, "We looked at different configurations, including a V-twin, which we prototyped. But the parallel twin is the best solution. It requires fewer parts, like cams and cylinder heads, so is less expensive to produce and easier to package as it is shorter".[15][16]"