alternators?

Probably had something to do with the underhood packaging -- i.e., easier to find places for two small units rather than one large unit. Interesting to note that they did use one larger alternator on the 365 GT4 2+2, but, with the added injection stuff on the 400i, might have made the room more difficult to find. Or could be trying to share part commonality or a supplier issue -- the early 308 also used a Bosch 55A alternator.

You could ask the same thing about why two injection systems and not one big one, or why one distributor and not two like most other F models. Sometimes putting it all in one big unit isn't the best way to go -- i.e., you should be thankful that they used two inexpensive off-the-shelf 6-cylinder Bosch fuel pumps rather than some horribly expensive custom single fuel pump on your 400i -- but the extra V-belt for two alternators is a real negative IMO, and it is surprising they didn't try harder to not do that. Historically, I think the two alternators on the 12-cylinder engines have proved troublesome, and they finally went back to one larger alternator on the TR -- but even that had problems needing more power than a V-belt could reliably transmit so they had to change to a multi-rib belt drive. Just some random thoughts...

 

I was quite pleased that there are two alternators when the belt on the upper one snapped - it enabled me to continue driving for a while and get the car to a garage.

Aidan