The Yammie XS crankshaft is very different to the Commando, It has 4 main bearings for the crankshaft alone, in that each con-rod has its own pair of small flywheels with a main bearing on either side, that is one each in the outer case and 2 side by side in the centre of the crankcase. The crankshaft centre is a spline fitting to combine the inner flywheels and this is simply pulled apart, rotated and refitted at 72 or 90 degrees depending on what you want from the motor. Because of the centre crank bearing support and 2 smaller flywheels the primary and secondary vibration effects are quite different to the Commando with its one massive flywheel.
The Iso frame was designed to cater to the out of balance forces with 60 - 62 % balance factor, mainly to provide a fore and aft effect so there would be little advantage to use the 90 degree crank version in the Iso frame. However, there is considerable history of many British twins re-phased in rigid frames, with improvement in primary balance and possibly torque characteristics, being similar to a Ducati or Guzzi. The disadvantage is that Commando big end journals remain seperate , i.e. spaced apart not common as on the Ducati so a rocking couple effect happens - drive and timing shaft extremities alternately want to go up and down. That potentially might be all wrong for an Iso frame as side to side vibration but may not be a problem in a Featherbed or other rigid design.
Mick
