Archive of BMW Motorrad Club Cape (2006 - 2019)

Are you talking about the aluminium plate at the end of the swingarm, one on either side, with a bolt for tensioning the chain?  If so, it should not be loose.

Did you put a screwdriver between the chain and sprocket and turn the wheel so that the chain was tight before you fastened the axle nut?  Had you adjusted the chain tensioners to the same distance?  If you did, and the chain tension is correct and the wheel is aligned, then just torque up the chain tensioner bolts so they don't come undone while you are riding and fall off.

What Charles said...