I'm having some disturbing thoughts about all of this.......... On the BMW the rotor is on the end of the crankshaft isn't it?
On the 1150 the alternator is belt-driven. On the earlier 450/650/700/800/900/1,000cc "Airhead" motors they were on the end of the crankshaft. I also have a 1988 R100 GS 'Bumblebee' with this set-up. These are only 250 Watts though (400 Watt conversions available).
The latest 1200 GS with watercooling has the alternator at the back, gear-driven.
My 'VH' doesn't appear to have a fibre gear, it seems to be all-steel so I hadn't seen this as a problem (providing I remember to fully-retard the ignition before lunging at the kickstart)
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH