front sprocket nut

[fazersharp]

Here's some competition for the later-bikes-have-an-undersized-shaft theory:
a) the nut was underspecified
b) early Fazers had it glued on with a ridiculously strong threadlock (hence the need for a scaffolding pole extension on the socket to shift it )
c) Yamaha realised they'd made the bond too strong and switched to a different compound on later Fazers which proved to be inadequate
d) when owners/mechanics replaced the sprocket, the thread was contaminated with oil and they didn't use high-strength superglue hence subsequent failures on early bikes
e) Yamaha's instruction to dealers regarding shaft replacement relied on a measurement of the diameter of the threaded portion not because they'd made some too small, but as a means of determining whether the thread had been too badly damaged by the loose nut and/or sprocket.

Also my pet theory is that the original 98s shaft was only produced in 1 factory and it was after 98 when production stepped up that other factory's were brought online to produce the shafts which were undersize. So all 98s are ok and thereafter its a game of chance where your shaft was made as to whether or not you have the issue because remember that not all 99 onwards have the issue. And ones yam found out they made sure the shaft spec on new bikes was correct