You do NOT Have to remove the gas tank.Its pretty straight forward once you get the cover off what i remember.Its been like 60,000 miles ago.
Change Alternator Belt
Tools Parts8. Check the belt for proper tension (see above) and proper seating alignment.
T-handle hex – 4mm alternator belt
socket – 13mm
wrench – 13mm
1. Remove the four bolts holding the black plastic alternator belt cover at the front
of the engine, 4mm T-handle hex.
2. Remove the cover by sliding it straight down.
3. Loosen the 2 nuts and 1 bolt, 13mm, that hold the alternator – one is on top
and one is on each side, thus allowing the alternator to pivot down.
4. Remove the old belt.
5. Install the new belt being sure it is properly seated.
6. BMW calls for a tensioning torque of 5.9 ft.lb. (8 Nm) on the adjuster bolt on
the left side of the bike. You have to get at this bolt from the alternator side and
you may have to lift the tank. Alternatively, you can pry the alternator up with a
large screwdriver to tension the belt.
7. Once the belt is under proper tension, tighten the 2 nuts and 1 bolt, 13mm, to
15 ft.lb. (20 Nm).