Bosch Alternator Refurb...

Discussion in 'Electrical' started by Zender Z20, Jan 12, 2024.

  1. Zender Z20

    Zender Z20 Paid Member Paid Member

    Joined:
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    Location:
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    So... did the MK2's old starter motor in another thread and thought since I was on a roll would do the same for it's original alternator.

    As far as I can remember (was 12 plus years ago) it worked fine before the car was laid up, but a new one was bought regardless when the time eventually came to get the car back on the road, with the one below now being a spare.

    Biggest issue was getting it apart, of the 4 x through bolts that hold the front and back sections together one refused to move and even taking it carefully the slotted head was starting to give up.

    Plan is to get some hex socket head replacements so if there is a next guy he doesn't have the same problem.

    Eventually had to drill it out, but once the casings were separated there was the room to get a good grip / undo the remains of the bolt shaft in a vice.

    Other than that it was a clean up job and repaint of some internal parts so as to future proof them against rusting again.

    The front / rear bearings were spot on with no play whatsoever, which was handy as I've not the tools to replace them, though it'd still likely be cheaper getting someone to do it than buy a complete new unit.

    There's a white plastic cup sits in the rear casing, just pushes in hand tight. The rear bearing sits in it, again pushes into it with nothing more than finger pressure... the bearing must be so freely moving that it doesn't require anything more than that to keep it in place, obviously works fine (this one had 75K on it and still like new) but just seems a little under engineered!

    Apart from that oddity the remainder of the insides of these things look like they were made in a ship yard, I can't imagine you'd easily physically break one so am guessing if they do fail it'd probably be the bearings or better still the voltage regulator / brushes that've gone.

    The regulator is a two screws to take off / put on job, couldn't be easier. Bosch still do them (if a little pricey) but there's plently of cheap aftermarket ones too.

    Since learned you can bench test alternators, plenty of explainations on line, though I didn't have the luxury of an ammeter to verify that side of things, but a cheapie eBay one's on order.

    (Someone'd apparently had the pully off before me and hadn't replaced the woodruff key, hence it not being on in the finished pics. until a replacements got.)



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  2. Zender Z20

    Zender Z20 Paid Member Paid Member

    Joined:
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    Location:
    1983
    Not sure why, but it wasn't as straight forward as you'd image it should be to get new through bolts.

    The originals are M5 x 105 (though 7Zap says it's 111mm), but they're stamped 9.8 tensile strength... I'd not seen that one before either.

    That though wasn't the issue, it's probably overkill but 12.9 are pretty common, it was instead the threaded length that proved the stumbling block.

    Originals are 35mm, which seems to be a bit of an odd one, but fortunately it turns out 25mm will do.

    You can see the witness mark on an original against a new hex head one and coincidentally it appears the threaded part of the back casing is exactly 25mm in depth.

    Maybe they use the same bolts on heavier duty /deeper bodied alternators that take up the excess thread?

    So, if you're in the market for new bolts, click https://www.ebay.co.uk/itm/152176787394?var=451371226412 for a pack of five / £2.89 posted.

    Woodruff now got too... all is once again right in the world.



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    stephen stanyer and Rustbuster like this.

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