Eight valve twin with troublesome chain driven balancer. Good frame but engine burns out valves, strips plug threads and needs constant fettling. Early B model had two piece cylinder head that leaks oil. C model quickest, E model slowest; D model on had easier to adjust balancer chain. Ferodo pads cure wet weather lag. Avoid 2-1 exhausts. Some ran for 50/60k but the majority expired rapidly.
