The XS engine is meant for running 130 tire in the rear. I'm running a 250 tire. That extra 120mm means the engine's sprocket won't line up at all to the rear tire, unless one of them is offset 6cm. But that wouldn't make for a very balanced bike, so instead a mechanism needs to be made to offset the drive chain.
This jackshaft system is pretty straightforward, 2 sprockets on a shaft, the shaft spinning in a pair of bearings. The function should be clear, but the assembly is best understood in motion.

Jackshaft Video

The sprockets were just 2 more of the stock Yamaha drive sprockets. The shaft diameter was chosen in concert with the pillowblock bearings, first for how heavy duty they needed to be and then for a size small enough to fit in the frame with enough room to allow the pillowblocks to slide back and forth to adjust for chain tension.

With the sprockets, bearing placement, and tire placement all sorted out, measurements could be taken to put in the order for the jackshaft to be machined. In the final weeks of the project it was sent in. Slack was kept in the distance between the sprockets to account for error, so alignment fine-tuning could be done by the width of the spacers.

email: mikebike@rocketcar.net