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Thread: Alternator PULLEY ~ E87 120i

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    Default Alternator PULLEY ~ E87 120i

    Here is a photo of the Alternator and its pulley.
    The serpentine belts runs in the six or so Vee grooves on the pulley.
    According to some forum/ posts this free-wheel pulley that somehow seizes-up and makes a noise.
    The free-wheeling allows for charging on the overrun. An economy consideration.


    Anyone know how this pulley comes off and apart? I believe the end part of the pulley is merely a cap which when removes revels a retaining bolt.
    Anyone know how it (the free-wheel) works?
    I understand you can buy the pulley separately. Part# Bosch 6PK 12 31 7560 483 (I think!)
    Also, these free-wheel pulleys are used on most BMW alternator


    RegardZ.
    Last edited by GarnZ; 22nd July 2015 at 07:08 PM.

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    From a quick google, looks like you need a locking tool to stop it from turning while undoing the bolt, I would assume it is similar to a ratchet where it has a loaded lockout inside with a gear against it (think wheel of fortune wheel style). If the little locker gets stuck then the gear cant turn properly or at all. Ive never actually come across these myself so out of interest, does it freewheel both ways? If so, it may have a sort of clutch inside that slips when the engine quickly changes revs meaning less drag on acceleration and a continual running while the engine slows down. (If that doesnt already exist, then maybe it should :P)

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    Quote Originally Posted by Blade695 View Post
    From a quick google, looks like you need a locking tool to stop it from turning while undoing the bolt, I would assume it is similar to a ratchet where it has a loaded lockout inside with a gear against it (think wheel of fortune wheel style). If the little locker gets stuck then the gear cant turn properly or at all. Ive never actually come across these myself so out of interest, does it freewheel both ways? If so, it may have a sort of clutch inside that slips when the engine quickly changes revs meaning less drag on acceleration and a continual running while the engine slows down. (If that doesnt already exist, then maybe it should :P)
    Blade, thanks for your reply, the pulley is suppose to rotate both ways. I have been lucky to receive a video (from another forum) on the process of removal of same, I will post it up tomorrow. The video also states the damage that can be caused by leaving this pulley unattended, if noisey. It is used in other models of BMW and there looks to be only two types (part #) available for these Bosh alternators

    RegardZ
    Last edited by GarnZ; 22nd July 2015 at 11:26 PM.

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    Here it is.. (compliments of Rammie ~BabyBMW forum)
    http://www.e90post.com/forums/showthread.php?t=1080557
    This is a scary, makes me think I can't delay in having this pulley replaced.
    RegardZ.
    Last edited by GarnZ; 23rd July 2015 at 06:45 PM.

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    I had the job done on the E87 Hatch auto (2005).
    The job consisted of .. new serpentine belt and replace alternator pulley.
    As mentioned, this pulley is called a "cush' "pulley, a "free-wheel" or an "over-run" pulley. It has seized causing a noise when cold starting and engaging in F and R.
    The noise has now gone!


    Here's a pic of the culprit





    This pulley screws onto the alternator shaft and is designed to drive the alternator via the belt. When the engine stops or slows, the pulley allows the alternator to free wheel, until running out of momentum. However, these pulleys, in some cases, at about 60 - 80K, cease to operate and the internals seize.
    Now, this in itself is not a big problem, as it would just act as fixed pulley (like they did in yester-year). If however, the internals, which must consist of small rollers, mal-functions and the pulley overheats, it can melt the thread and shoulder of the alternator spindle. That's my version anyway!


    BTW, there are many makes of cars with this 'cush' pulley and they can be troublesome... Skoda, Audi and VW.



    Some further thoughts ......

    Although the noise has gone, I fail to see how more damage could be done to pulley and belt once the pulley has seized. Remembering it is still free on the alt spindle bearings....
    Would'n't it just act as a fixed pulley?

    Maybe when seized, it may try to undo from the alternator spindle on the threaded section and rattle around continually, doing up and coming undone. Until it wears the end if the spindle out? Or becomes too eccentric to drive and does some real damage?
    Anyone?

    RegardZ
    Last edited by GarnZ; 16th August 2015 at 09:26 PM.

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    if it seizes, wouldn't the belt 'collapse/burn out'... then the other side of the belt would 'free wheel' the other driving point and cause problems?

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    Thanks for your reply, when this unit (pulley) seizes it merely locks up, so that the pulley unit is unable to "Free-wheel". Hence, my theory is that it would just act like a pulley that is locked to the alternator spindle. ie. Just like they used to be on older models without this special pulley.

    By looking at the pic, you can see a threaded section and a splined section, when it's working the threaded is locked to the alt spindle, when the alt stops or slows the splined section is allowed to over-run. When it has seized the splined section locks to the threaded section and the spindle.
    RegardZ.

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