To my knowledge, there are not any V-6 bikes and I have always wondered why not. With inline 6's, boxer type (GW) 6's and V-4's and many inline 4's, I always wondered why the V-6 was not an option. I know there is a problem with uneven pulse seperation unless the crankshaft rod journels are stepped, but that is a common thing now in V-6 car engines to increase smoothness.
RandyA