| The rear of the sprocket/renthal carrier is held in place by a large circlip.
This steel circlip in its groove on the ali sprocket centre tends to gradually wear the groove wider and wider and this lets the carrier/sprocket float a bit.
My 1997 916 Bip did this after about 40,000 miles.
I replaced it with the later 996 type which has a different ali centre and a separate spacer to prevent any rearward movement. No circlip -no wear.
If you have got a mate with access to a lathe/machine shop you may be able to shorten the old worn ali centre and turn up a spacer to go with it.
All you need are the dimensions from someone with a later model who is prepared to strip and measure it.
If you get the measurements let me know because my 98 916 will need doing sometime.
Steve B | 
Threaded Mode