The 650 Rotax models have a combined starter clutch, alternator stator and flywheel assembly on the RHS of the engine. There are part differences between the F Series and the G Series models. It appears the G Series starter clutch has been changed with most other parts remaining the same. The Part Nos are in the pdf. Generator Parts
The GS models have a 400 watt alternator while the X models have the earlier 280 watt alternator and it appears the flywheel is around 1kg lighter on the X. The 280 watt stator assembly appears to be 5 mm shorter than the 400 watt assembly and it is reported the 400 watt assembly has been fitted to an X model.
While it is not confirmed it appears the RHS engine cover is the same between year models other than color plus the BMW logo with 2 spark casting on the 05-15 models. It may also be possible to fit the lighter X flywheel to the GS.
The LHS diagram shows the rear of the flywheel and sprag parts. Viewed from the rear of the flywheel (engine side).
A pdf for the repair procedure below Repair Procedure pdf
Drain oil and remove wiring cover and engine side cover.
Position piston at TDC. (so woodruff key is on top)
An F650 classic is shown but the GS is basically the same.
BMW puller 125510 is needed for flywheel removal.
Be warned it may take considerable effort to crack
BMW recommend heating the flywheel to 80c (176f).
Remove freewheel housing from the flywheel. (4xM8 nuts)
BMW recommend heating the flywheel to 120c (248f).
The picture shows clutch removed and taped to hold parts together.
Remove new spring from seal & slide over taped sprag clutch
Cut tape from sprag clutch and ensure spring is seated.
Clean threads of bolts and flywheel then fit clutch to flywheel
Install the freewheel with the mark (arrow) down (to outside of engine).
Use Loctite 648 on threads and torque to 35nm
Fit circlip & Oil the freewheel in the freewheel housing
Check lock function and locking direction of freewheel
Clean crankshaft, woodruff key, flywheel and hex nut.
Apply Loctite 648 to the inner surface of the flywheel
Slide flywheel onto the crankshaft, align woodruff key and groove.
Rotate starter gear counter-clockwise if needed to fit flywheel.
Install the circlip and hex nut. Tighten hex nut. Torque is 180 Nm
Fit side covers, wiring and wiring cover (GS), then refill with oil.