[Ducati] 851 bearing

[mce.m at clear.net.nz]

I have had the little bearing outside the altenator rotor on my 851 fail 3 times. Second time was straight away and I know what I did wrong (didn't relieve side loading after pulling bearing on with the cover) but the other times have me stumped. Does anyone have an any idea what I may be doing wrong. Everything seems to be running true.
Thanks,
Mark
New Zealand