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Matt, Engineer
Category: BMW
Satisfied Customers: 21851
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Need To Replace BMW 645CI Alternator.

Customer Question

How to replace alternator on a 2005 BMW 645CI? I have all the bolts off but it won't "slide forward".
The battery is good. When car is running, volts begin to drop so nothing coming from alternator
Submitted: 11 months ago.
Category: BMW
Expert:  Matt replied 11 months ago.


On one of the mounting there is a cylindrical dowel that the mount bolt passes through. In order to remove the alternator you will need to push the dowel back into the alternator body so there's enough room to lift it off and away from the engine.
If you examine all 3 mounts to locate the one with the dowel pin and then use some swan neck pliers or a g-clamp to pull the alternator body forward and so press the dowel back in place.

Customer: replied 11 months ago.
There are only 2 mounts on the alternator, not 3 and both of those bolts are out.There is no dowel
Expert:  Matt replied 11 months ago.


this is the correct procedure

0) Remove the engine top cover, air box and intake elbow
1) remove the radiator fan assembly (front upper slam panel off, upper radiator plastic cover off, lift the radiator fan assembly and fold in the tab on the right hand side then lift free)
2) remove the serpentine belt (T60 Torx into the tensioner on a long bar, take off the tension, remove belt)
3) Remove the idler pulley bolted to the alternator (lever off the front plastic cover, unbolt the T50 bolt in the centre with a breaker bar)
4) If you can, remove the idler pulley bolted to the belt tensioner
5) Get the car in the air on jack stands
6) Remove the front under tray
7) Remove the two large bolts securing the alternator to the engine
8) Remove the two 13mm bolts securing the PAS pump to the same bracket to give you more wiggle room
9) Unclip the main positive lead going to the alternator from the metal clips (one under the throttle body, one on the passenger head and one above the alternator)
10) Lever, wiggle, pull, and eventually you will be able to rotate the alternator slightly anticlockwise while simultaneously pulling it forward, down slightly and it will come off the mounts and out past the oil cooler thermostatic housing at the back.
11) Now put something heavy in front of the radiator fins (I used a thick car mat) and pull the alternator forward and tilt slightly vertical (drive pulley facing upward) till you can get to the 13mm battery +ve nut and the small clip-in connector at the rear. Undo these, you might have to get to the B+ nut from underneath
12) Withdraw alternator