Originally Posted by ducnut
A bicycle has a rear derailluer that acts as a chain tensioner. I'm not sure you could develop a tensioner that would be tensioned enought to withstand an 800cc motorcycle, yet, be slack enough to allow it the chain to climb to the higher gear. Also, the rear cassette has teeth shaped in a specific way, on a bicycle, to get the chain to climb the gears. Lastly, a motorcycle chain is designed to be ran only in a straight chainline, whereas a bicycle chain is designed to be cross-chained.
IIRC there are a few Buells that have a tensioners capable of handling engine braking, but, I would stay for the internal approach and have a sliding transmission gear with a manual dog, instead of one controlled by the shift drum.
That way the extra running gear stay clean inside the enlarged engine cases :-)