I was very much in doubt if I should include this chapter or not, because every indication given on the expected lifetime of specific parts will at best be extremely unprecise. You will probably discover great differences form this chart because owners does not treat their bikes the same way and drive under different conditions.

But anyway - here's my best shot.

Part	Expected lifetime
Piston rings	50.000 km with velocity stacks, significantly more with filters.
Piston/cylinder	At least 3 changes of piston rings if its the cylinders with Nikasil plating in the bores (Gillardoni). Most are.
Valves/guides/rockers	150.000 km.
Cam chain	80.000 km.
connection rod bearing shells	In any engine this is the bearing with the most load on it. Change it at 80.000 to play it safe. Failures on this bearing can be a real disaster for your engine.
Clutch	100.000 km. Very much depending on user
Crown wheel/pinion in rear drive bevel box	150.000 km.
Unijunction in drive shaft	50.000 km.

There's lots of other parts in the engine where I never heard anyone dare to guess at a expected lifetime, and I'll once more state that the figures above are very, very rough estimates.