[Alfisto Steve]

Reference Alfa tech bulletin 01.92.02
Aux Drive Gear Sets - distributor/oil pump drive gears must be replaced in sets or at least you must order gear with correct number of teeth to match old one.

Note that early 164 engines used same gears as GTV6 and Milano but without VIN number to match engine number you have to be careful that you don't mix up gears.

This is why when I help somebody get valve and head repair I ask that both aux drive shaft and gears be shipped with their core rear head in case they don't match exhange head.

 

[AlexGS]

Interesting - so, when there was no longer any need to provide a distributor drive (at half engine speed), the gearing was changed to speed-up the oil pump. I wonder if this was an attempt to raise the oil pressure when idling!

-Alex