THREE BIKES ONE ENGINE

Honda's largest parallel-twin engine manages to cater for an incredibly varied trio of platforms, with the Rebel, NT and Africa Twin being just about as diverse as they come. We ride the Japanese firm's cruiser, adventure bike and commuter/tourer models to find out just how one powerplant can be suitable for all three.

- Dave Manning

The engine that we're looking at here, at 1084cc, may not be the biggest capacity on the market, but is nonetheless quite sizable for a parallel twin, especially given the current glut of twins that are in the region of 700-900cc. The Honda big parallel twin's configuration is - like the 750cc powerplant in the new Hornet and Transalp the Unicam, in which just one cam is used to operate both the inlet and the exhaust valves, with two of each per cylinder. Initially, this seems like something of a retrograde step when you remember that motorcycle development with Honda went from the SOHC 750 four launched at the very end of the Sixties to a DOHC inline-four a decade later, which was much the same with just about any engine development programme that you can think of. The process of poppet valve to sidevalve, to overhead valve, to overhead single cam and then overhead double cam looks to be irreversible, but Honda has contradicted that to a certain extent with the new 750 and 1100 twins. Of course, the change isn't simply a reversal of technology, as there is a technological reason behind the return to a single cam that actuates both inlet and exhaust valves. A single cam not only weighs less than two (clearly), but also it takes up less room, and the space that has been saved can be used for an expanded airbox feeding downdraught throttle bodies; for a change in frame design; or for a reshaped fuel tank. Or all three. And, partly thanks to the friction-reducing roller followers on the operating arms (leading to screw and locknut adjusters atop the valves) there is no potential loss in engine performance. The only issue that might arise would be when tuning the powerplant and an alternation in valve timing was required, as an adjustable cam sprocket would change both exhaust and inlet timing together when for the required tuning they may need to be changed independently.