The Kymco-built BMW 650 power unit drives a fully enclosed chain running in an oil bath, concentric with the swinging arm. This is similar to the arrangement on the first 3 versions of Yamaha's Tmax, but different from the exposed toothed belt drive used on the Mk4 Tmax530.
In contrast to all 4 Tmaxes, the BMW's final drive is single sided, and also benefits from an easily accessible and adjustable rear shock absorber. PNB
Image: BMW