is 5mm = what stands out of the voltage regulator, here shown for the M30 engine http://workshop-manuals.com/bmw/5_se...ulator_switch/
Check slip rings for wear, disassembling alternator and fine-grinding as well as polishing slip rings if necessary.
Check for truth of running of slipring. Max. eccentricity for slip rings is 0.03 mm.
http://workshop-manuals.com/bmw/5_se...h_alternator)/
Disassembling and assembling Bosch alternator 90/115/150A
http://workshop-manuals.com/bmw/5_se...90_115_140_a)/
Replacing ball bearing Bosch alternator
http://workshop-manuals.com/bmw/5_se...h_alternator)/
Replacing diode plate Bosch alternator
http://workshop-manuals.com/bmw/5_se...h_alternator)/
Electric test on Bosch alternator
http://workshop-manuals.com/bmw/5_se...ch_alternator/
Replacing alternator belt pulley
http://workshop-manuals.com/bmw/5_se...r_belt_pulley/
Replace alternator belt pulley with overrunning clutch
http://workshop-manuals.com/bmw/5_se...nning_clutch)/
This shows my original Bosch regulator after 150000 km and the new Hella voltage regulator I installed, the old one was definitely at the end of it's lifetime http://www.bimmerboard.com/members/s...%20241_131.jpg
After I installed the new voltage regulator I also got better volts shown in the OBC.
Alternator repair DIY http://www.rangerovers.net/repairdet...haltrepair.htm