To fulfill basic performance requirements as a sport bike while setting higher targets for environmental performance, a DOHC was chosen as the valve system. DOHC improves combustion efficiency by reducing the weight of the reciprocating portion of the valves. This selection also allows us to freely choose the included valve angle, the port shape, and the shape of the combustion chamber. The choice of DOHC contributes to improved product appeal as a sports bike as well as to performance.
For the valve system, a roller rocker arm was adopted by a DOHC engine motorcycle for the first time in the world. A low-friction valve train with a smaller cylinder head was achieved through an ultra-compact layout for the roller rocker arm.
The choice of a shim design for valve tappet adjustment reduced the rocker arm weight, while friction was reduced by setting the valve spring load to a low level.
For better maintainability, the shim can be replaced without removing the camshaft.
Roller rocker arm
Silent cam chain (SV chain)
Cross-sectional view of cylinder head