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Thread: Procedure to change alternator

  1. #1
    Join Date
    Oct 2010
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    1991 BMW 850i

    Procedure to change alternator

    I need to change my alternator and was wondering if anyone had good instructions for the procedure OR is this something best left to a shop. I have been quoted about 4 hours of labor for the work by the shop so I'm evaluating if this is something I should consider doing myself (and I don't have a lift) OR let the shop handle it.

    As always, any insight or help would be appreciated.
    ========
    91 850i 6-speed, 2018 M550 - wife mobile, Lexus GX460 - Family mobile

  2. #2
    Join Date
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    Can be done in about 1 hour. Drop it in from the top (even though people swear that it can't be done), I just did this last weekend. No problems.
    '93 850Ci - Mineralweiß Metallic

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  3. #3
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    koenig ks8 /e31 850c
    disconect the batteries or you will have a fire!

  4. #4
    Join Date
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    not enough
    not a bad time to replace that alternator wire (if not done already)
    CB42366 - 1991 850i 6-speed. Brilliantrot & Black Nappa Leather
    CD00144 - 1994 850CSi. Hellrot & Black Nappa Leather


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  5. #5
    Join Date
    Dec 2007
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    El Dorado Hills, CA
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    Quote Originally Posted by TxGR8White View Post
    Can be done in about 1 hour. Drop it in from the top (even though people swear that it can't be done), I just did this last weekend. No problems.
    +1. Just start removing the parts that are in the way from that side. This will give yourself some room to work. I have also done this from the top. A tight fit but if I can do it you can too. No problems on this end after the install. Just take you time. Hope this helps. Cheers, Carter

  6. #6
    Join Date
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    '93 850Ci- Daily Driver
    The key here is to remove the MAF , the MAF elbow, the upper airbox with airfilter, and disconnect the radiator hose. What I did was to "tie" the hose back towards the master cylinder so that the coolant won't run out.
    You will need to completely remove the belt tensioner assembly in front of the alternator (take a quick pic so you can see the belt routing).
    The most difficult part is to remove the two wires on the back of the alernator itself.
    It is adviseable that you remove your alternator first and take it down to the auto parts store so they can remove the pulley/cooling fan assembly from your old one to put on the new one. This requires an impact wrench - it is difficult, if not impossible to do with ordinary hand tools.

    Good luck!
    '93 850Ci - Mineralweiß Metallic

    2001 740iL - Titansilber
    ALPINA B7 -Alpinweiß III


    ...the price of cool ain't cheap!

  7. #7
    Join Date
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    So after a lot of deliberation and more online research and after going through some of the advice I got from folks on the forum I decided to tackle the task myself. I was able to do the following:
    - Disconnected batteries (which I replaced with new ones since the older ones were about 10 years old)
    - MAF removed
    - MAF elbow removed
    - top of the air box including the filter - couldn't remove the rest of the box since it is connected to an elbow under the headlights and I couldn't find an easy way to remove it - any suggestions here? Hope I don't have to remove the headlights .
    - Radiator hose removed and tied it back to avoid coolant running out
    - Removed the distributor cap and tied it back.

    So I think all of the above is the easy part.

    The next step was going to be removing the belt tentioner. I guess I would need to remove the fan for this as well which I understand requires a special tool .

    Now the one thing that I can clearly see is going to get in the way is a hose + metal pipe combination (see attached picture). I took the pic from this site: http://bmwe32.masscom.net/sean750/al...eplacement.htm which has this procedure documented - however he removes the radiator as well.

    So I'm looking for some ideas on the best way to remove the air box as well as thoughts on what else needs to be removed to get the alternator out. Is this metal pipe/hose going to pose problems.

    Is removing the radiator recommended? If so I'm inclined to put the car back together and let the mechanic do this for me - starting to get outside my comfort zone and I don't want to do something stupid. Also I understand that the alternator bolts aren't very easily accessible either - at least the one on the bottom.

    Good news is that my alternator cable seems to be in really good shape.
    ========
    91 850i 6-speed, 2018 M550 - wife mobile, Lexus GX460 - Family mobile

  8. #8
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    '93 850Ci- Daily Driver
    - remove the fan - reverse threads on the nut! left is tighten, right is loosen.
    - no need to remove the lower airbox (where the airfilter resides), leave it bolted to the fender.
    - no need to remove the radiator.
    - piping you refer to is not in the way.
    - you will need to remove both of the nuts on the back of the alternator to get the wires off. This is a good time to splice in a plug on the small wire to make it easier next time you have to remove it.
    - belt tensioner will need to be remove - no big deal. just move the belt to one side once it is off. You might also want to take a pic before you remove it so that you know the belt routing upon reassembly.
    - you might also want to unbolt the distributor cap, and move it to the side (next to the oil filter canister), for more room.

    That should do it - reassembly is in reverse order.
    Good luck.
    '93 850Ci - Mineralweiß Metallic

    2001 740iL - Titansilber
    ALPINA B7 -Alpinweiß III


    ...the price of cool ain't cheap!

  9. #9
    Join Date
    May 2010
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    Brentwood, NY
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    BMW 850
    Quote Originally Posted by TxGR8White
    - remove the fan - reverse threads on the nut! left is tighten, right is loosen.
    - no need to remove the lower airbox (where the airfilter resides), leave it bolted to the fender.
    - no need to remove the radiator.
    - piping you refer to is not in the way.
    - you will need to remove both of the nuts on the back of the alternator to get the wires off. This is a good time to splice in a plug on the small wire to make it easier next time you have to remove it.
    - belt tensioner will need to be remove - no big deal. just move the belt to one side once it is off. You might also want to take a pic before you remove it so that you know the belt routing upon reassembly.
    - you might also want to unbolt the distributor cap, and move it to the side (next to the oil filter canister), for more room.

    That should do it - reassembly is in reverse order.
    Good luck.
    Perfect...I have done this A LOT recently.
    To add more details...
    I remove the bottom plastic skid plate to reach the bottom alternator screws. I also remove the screw that attach the Pentosin hard line to the oil filter canister to create more wiggle room. I move the alternator forward and tilt the back up (pully down) to remove the two wires. I pull the alternator with the pulley facing straight up. The snorkel turn towards the radiator seems to be a touch easier. Go slowly or it will get snagged and break old e31 plastic.

  10. #10
    Join Date
    Oct 2010
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    1991 BMW 850i
    Thanks Steffan and "thelongride". I managed to get alternator out. Steffan I agree that getting the pulley/cooling fan isn't going to be easy with hand tools - i guess this gives me the excuse to go buy that impact wrench I have been wanting to buy for a while .
    ========
    91 850i 6-speed, 2018 M550 - wife mobile, Lexus GX460 - Family mobile

  11. #11
    Join Date
    Oct 2010
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    Northern VA
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    1991 BMW 850i
    Thanks to everyone for their guidance and help. I ended up getting a new voltage regulator/brushes from Shogun and that seems to have fixed the problem.

    The car is back on the road now! On to the next project now .
    ========
    91 850i 6-speed, 2018 M550 - wife mobile, Lexus GX460 - Family mobile

  12. #12
    Join Date
    Feb 2014
    Location
    Louisville, KY
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    1993 BMW 850Ci

    Skid plates?

    Quote Originally Posted by thelongeride View Post
    Perfect...I have done this A LOT recently.
    To add more details...
    I remove the bottom plastic skid plate to reach the bottom alternator screws. I also remove the screw that attach the Pentosin hard line to the oil filter canister to create more wiggle room. I move the alternator forward and tilt the back up (pully down) to remove the two wires. I pull the alternator with the pulley facing straight up. The snorkel turn towards the radiator seems to be a touch easier. Go slowly or it will get snagged and break old e31 plastic.
    Does anyone have a pic of the skid plates on a 850 Ci? I have none.

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