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Thread: Alternator Shreds its Belt

  1. #1
    Join Date
    Jun 2015
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    91 735, 84 733, 84 633

    Alternator Shreds its Belt

    1984 633 CSI – 315k I have not owned this car for long and I’m working through several problems.
    The alternator wears the belt very quickly. It wears the tapered side or sides of the belt which becomes very thin and eventually slips and breaks.
    The toothed adjustment mechanism is in bad shape and I’m in the process of fixing that although I’m not sure that’s the root cause of the problem as it is possible to properly tension the belt.
    I decided to replace the alternator mounting bushings with urethane bushings although the alignment looked OK and it turned out the ones that were in there were OK. They must have been replaced not so long ago.
    Which brings me to my question. One bushing had the circlip facing the front of the car (see photo). The other bushing had the circlip facing the other way. It’s so long since I changed out alternator bushings that I don’t remember which way they are supposed to go . . . or if it matters!
    Any help or advice regarding the correct orientation would be much appreciated.
    Also if anyone can throw some light on the mysterious belt shredding that would also be most helpful.
    Thanks, John aka Kenneth

    Alternator.jpg

  2. #2
    Join Date
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    2002 BMW X5 4.4
    I had the same problem with the alternator belt on my boat. The problem was rust on the pulleys. After three sets of belts, the problem went away. The engine had not been used for a year and in the marine environment rust bulds up quickly.
    Never had the problem on the M30s or S38 in the M, but they never sat more than a month with idle engine.

    Sent from my SM-T377V using Tapatalk

  3. #3
    Join Date
    Sep 2016
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    1983 633csi, 2017 540i
    That pulley does look pretty bad.

  4. #4
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    86 635csi 98 740i 96 MB
    Yeah, that pulley looks so pitted it's probably chewing the

    edge of the belts apart.

  5. #5
    Join Date
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    '86 635CSi, '08 128i
    I think those circlips are in the correct orientation. I usually replace the M30 alternator with an M20 unit when chasing down E24 problems. It's not a perfect fit (pulley is offset slightly to the rear), but I prefer the solid aluminum E30 case over the bushed E24 alternator.

    The amperage is slightly lower depending on the M20 version, but I haven't noted more NVH. Swapping the smaller overdrive M30B35 pulley might bring those amps up a little. I'm also told there's a SAAB alternator with higher amperage that's a pretty easy drop-in.
    Save the manuals!
    '08 128i 6MT, '86 635CSi 5MT (B32, Motronic 1.3, WBO2, G265, 18# FW, 3.46 torsen)
    Past projects:
    '96 318iS, sold 4/23 '90 535iM, RIP 1/23 '90 535iA RIP 6/22 '91 318i, sold 7/19 '97 M3 sedan, sold 11/18 '85 735i, RIP 2/18 '92 325iC, sold 7/16 '91 318iS, sold 6/16 '84 745i, sold 10/14 '82 633CSi, traded 9/12 '90 325i, RIP '87 325 sold '89 525i, traded '87 325iS, RIP

  6. #6
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    89 635CSi, Nissan Murano
    That pulley looks shot to me too, I would bet that's your problem.
    SprCpe
    1989 635csi # 3268410
    Built in Germany with love.
    Ostatecznym maszyny jazdy BMW

  7. #7
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    I agree, the pulley is nasty, the car sat for at least a year before I bought it. I will address the pulley issue although I think it's contributing to the problem I suspect it's not the only cause.
    - I'm having a problem locating a pulley, new or used. Anyone have one available?
    - Or anyone have ideas to re-finish or smooth the old one?
    Also, I think I have found the answer to my own question regarding the orientation of the circlips on the alternator mounting bolts. See attached picture courtesy of Bosch and Rockauto
    Alternator bushings.jpg

  8. #8
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    Try emory paper on spinning pulley, just to remove most of the surface rust.
    I realize that the adyustment is limited, but try a 13mm wide belt instead of the 12mm that is stock. It will have to be a little longer. Run that for a few hundred miles, or until groove in the pulley looks smooth, them go back to proper belt - be carefull not to overtighten the belt, the waterpump will not like it.

    Sent from my SM-T377V using Tapatalk

  9. #9
    Join Date
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    1982 628CSi
    The pully consist out of two separate parts and when taken apart are like two saucers with the backs against each other. This makes it very easy to remove rust and to do a fine sandpaper smoothing job. Don't forget to use something like zinc spray to protect it from future rusting.

    My own alternator:

    and the pulley:


    after the rebuild:
    Last edited by Nullified; 03-23-2020 at 04:49 PM.
    Undergoing restauration; my 1982 628CSi: https://www.bimmerforums.com/forum/s...628CSi-rebuild

  10. #10
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    Thank you Nullified. Question, what is the best way to stop the shaft turning to remove the big nut?
    Also, regarding my other question, referring to your photo, when reassembling the circlip is at the front on the right and at the back on the left.

  11. #11
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    81 euro 635, 4.4 X5
    Put the belt around the pulley and :"choke" it down while holding it. That should stop it from turning or put a box wrench on the nut and give it a sharp wrap with a hammer which should break it loose. Try the belt first it should be an easy solution.
    Last edited by Bert Poliakoff; 03-23-2020 at 10:24 PM.
    81 Euro undergoing total nut and bolt restoration
    pictures at: flickr.com/photos/bertsphotos

  12. #12
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    The alternator is shown from front, then back. Or the other way. I did not show the same side before and after.

    - - - Updated - - -

    Use a screwdriver to lock.

  13. #13
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    Best way to remove rust is media blasting.
    I use glass bead to remove rust. Check with
    body shops in your area. Two small discs
    won't cost that much. Here is before and after
    glass beading then powder coat.

    IMG_0637.jpg
    IMG_0631.jpg
    Last edited by 1986series6; 03-24-2020 at 05:08 AM.

  14. #14
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    BMW 645 E64 2005
    had same issue with my 635, i used a belt tension from an E28 or E32. did small mods on fitting and it worked out great.

  15. #15
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    Problem Solved - Cautious Optimism

    I cleaned and smoothed the inside faces of the pulley using coarse and then fine emery - wet and dry (dry)
    I stole the adjuster off my 733 (not running) as the adjuster "rack" was actually cracked on the 633.
    Installed new polyurethane bushings (see picture)
    Assembled with all the right nuts, bolts and washers and a new belt.
    Alignment came out reasonably good (photo distorts the alignment, it's actually not bad)
    Was able to tension the belt properly.
    Have put a few miles on it, nothing too fast.
    By now it would have shredded the belt but belt tension still OK and no sign of belt wear.
    Also, added benefit, water pump, fan etc functioning properly now and temp gauge is steady at mid range.

    Sidebar: I read Mike Self's column in this month's Roundel with some empathy having just installed the urethane bushings. Like Mike, I had installed some years ago on my '79 Euro (they were the red ones) and I remembered, you had to compress them to get the circlips installed. I used a good sized G-clamp which worked well. I bought the Ricochet bushings on Ebay. They look nice, (see picture) and fit the bore OK if you push them in with the clamp but the flanges on the bushings are a bit thicker than the originals and I had to compress the daylights out of them to the point where I'm a little concerned about the circlips holding (the grooves are not very deep) They certainly make for a good connection with the bracket and adjuster which is what I wanted for alignment.

    Sidebar II: Off topic - I enjoy Satch Carlson's column on the last page of Roundel, Satch drove a Ferrari in the 1988 Mille Miglia Historico. Sterling Moss drove the Mercedes 300SL in which he won the 1955 Mille Miglia with Denis Jenkinson (read the account if you haven't done so already) Sad that we lost Sterling Moss in April, I saw him drive once but not one of his great races.


    Alternator Bushings I.jpgAlternator Bushings II.jpg

  16. #16
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    Just want to say it is still not aligned properly.

    Looking closer maybe it's the angle of the photo
    that causes the casing to look like it isn't parallel
    with the belt.
    Last edited by 1986series6; 06-24-2020 at 08:56 AM.

  17. #17
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    Alignment came out reasonably good (photo distorts the alignment, it's actually not bad)
    I worked as a mechanical draftsman many years ago, old school, tee-square and adjustable triangle! I still have a good eye for straight and level.

  18. #18
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    I'm just about to retire from printing that also used t-squares and triangles so it must be
    the distorted image.

  19. #19
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    I would have put the thing is a vice, used a drill with proper sized socket, spin the shaft while applying emery paper.....and Bob, your image is not distorted with those of us in the Idiotfest crowd....I mean we demand that to fit in anyway.
    Rob E3

  20. #20
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    Hey Rob,

    Your right, I am an IDIOT and should have realized that from the get-go. Here's wishing we can meet this Fall.

  21. #21
    Join Date
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    '92 325IC '88 635
    Here's a solution: If you wanted to , you could get a bracket used on the B35 engines. They are much more robust and don't have the alignment issue due to the bracket supporting the upper part using both sides of the bolt boss. This eliminates any of the twist associated with using just one side on a thin adjusting bar. I think it would just bolt on your original mounting pad. I just don't know if your B34 alternator casing would fit the new bracket. You could always get a B35 alternator and it all would match. See pics of the bracket and how it would look mounted. Pics are from internet images. Edit: Oh, and Happy Friday you friggin Idiots!! Bob and Rob

    B35 Alt adjust bracket.JPG B35 Alt bracket mounting.JPG 86 635 engine.JPG
    Last edited by carsnplanes; 06-26-2020 at 07:09 AM.
    '88 635, '92 325IC

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