On Alfa number 15
AO Platinum Member
Join Date: Dec 2005
Location: United Kingdom
I think the V6 has a taper and the TS a Keyway.
I have heard of the keyway shearing off, but it is rare. It could be that it was disturbed when the belt was changed, of it could simply be that you have been very unlucky...
If you think about it that keyway isn't just under load from the cambelt, the auxillary belt pulley is bolted to the cambelt gear, so the keyway takes the strain from the aux belt circuit as well which includes the PAS, alternator and aircon pump.
If any of those fail and create extra load it could also cause the keyway to shear.