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Reconditioning a magnetti marinelli A127 Alternator


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I had an old alternator sitting here, so I thought I've have a go at reconditioning it.

My local auto electrical place wanted €80. I bought the parts for €20.

This alternator is found in lots of LR vehicles, Ralph will tell you exactly which ones. ;)

It's pretty straightforward. You'll need a high wattage soldering iron and a selection of sockets to use as drifts for the front and rear bearings. To remove the front bearing, it needs to be supported by a piece of pipe, bigger than my largest 32mm socket.

Here's what you get in the kit;

Regulator/Brush box, rear bearing, slip ring, front bearing and rectifier.

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Using a hex drive in the centre of the shaft, remove the nut, pulley and fan

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Remove the 3 bolts securing the regulator. Remove the regulator and unplug the connector.

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Remove the single self tapping bolt located under the regulator. This holds the rectifier in position.

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Remove all bolts from the terminals.

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Mark the position of the front bracket, stator and rear bracket with tippex so that you out it back together the way you pulled it apart.

Remove the 3 through-bolts holding the alternator together. These are splined and need to be gently tapped out.

Then remove the rear of the alternator.

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Unsolder the 3 wires to the rectifier, noting their positions. These are reasonably large connections, so you'll need a good amount of heat.

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Remove the rectifier

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There are 2 wires that connect the slip ring. Open each crimp, and remove the wire.

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Remove the slip ring. This was easier said than done, and I ended up taking a cold chisel to it. :ph34r:

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There copper wires sit on an insulator under the slip ring - be careful not to crack or break it, if using excessive force to remove the slip ring.

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Drift the new slip ring into position ensuring it is lined up with the 2 wires.

Check your drift bears on the plastic of the slip ring, not on the copper.

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Crimp the 2 wires to the slip ring.

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To change the front bearing, remove the stator and carefully tap the rotor out of the front bracket.

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Place a pipe of suitable diameter under the bracket and drift the bearing out.

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** The bearing is very tight and the housing is brittle. Make sure your supports and drift are exactly the correct size. I didn't and cracked the front housing. Not a problem as I'll swap the housing when I swap it for the alternator in the truck, but you don't want to be doing that to your only alternator. :(

To change the rear bearing, again make sure your drift is larger than the shaft diameter, and your support will allow the bearing to be drifted into it.

Then drift in the new bearing.

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Refit the stator and rotor.

Place the rectifier in position and clamp the wires.

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Solder the wires in position. Use lots of heat and allow the joint to sweat for a few seconds before removing the iron.

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Replace the insulators on the rectifier in the correct position.

Refit the rear housing, feeding the regulator feed wire through the hole.

Refit the terminal washers and nuts.

Refit the self-tapper securing the rectifier to the rear housing.

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Refit the through-bolts and tighten. Check the alternator rotates freely. If not, loosen the through bolts and re-adjust.

Refit the regulator/brush box.

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Refit the front bush

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then the fan and bush,

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then the pulley, split washer and nut.

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Thanks to Ates for the artistic photos :D

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great post! :)

You forgot the paperclip from the brush pack - don't want to damage those nice new brushes. :)

Where did you buy the kit from?

I was remembering white90s post about the paperclip but found that if you're careful, you can press the brushes into position without it.

Otherwise, there's the paperclip method

Got the kit on Ebay.

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Sorry Luke, saw his post in the tech archive on changing the regulator with the same method and assumed it was his :banned:

Apologies for the mis-credit :)

No worries,

The tech archive posts are "copy & paste" versions of the originals, I though the orginal author was credited in the sub-title.

Edit:

A127 Alternator regulator replacement, By Luke

I was :)

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If you are careful there is no need to unsolder the diode pack. Once you have removed the rear cap, gently insert some thin screw drivers between the iron ring of the stator and the top cap. You can gently then lever the front cap free from the stator and diode pack without unsoldering it. In fact when i rebuild these, i do this bit first after taking out the through bolts, lifting out the rotor and end cap complete from the stator and rear cap.

I never bother changing the rectifier, they very rarely fail on the 65a unit (unlike those fitted to 1980s version of a series 3 alternator..)

Sometimes the rotor shaft will be a very tight fit in the front bearing - its then 3 legged puller time to release the rotor...

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Good repair instructions, if i may add a small bit to it and that is sometimes you might

have to turn the two slip rings on a lathe as they are not usually true and you might experience brush bounce

sometimes you can use the old comm end bearing in the lathe as a guide

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  • 2 years later...

Just reco'd the A127 from my Discovery, this guide made it easy! Thanks!

Almost came unstuck with the front bearing, didn't have any pipe the right size. A bit of stainless bent into a tube did the trick!

$30 for parts is a lot better than $320 for a new alternator.

Cheers,

Scott.

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I did this to an old transit alternator (same A127 model), and it didn't work.

Turned out the insulation had broken down on the big coil (Stator?) meaning it was shorting out.

Something to bear in mind before spending out on the rebuild kit. Only problem being you need to take the thing to pieces to find out whats actaully wrong with it.

Given the time involved and the fact the repair kit was £20 and a recon alternator was £50, i would just be buying a new one after my experiences with the transit one

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  • 5 years later...

Pics are showing - it maybe your browser settings...

100A version is similar but the rectifier and regulator are different and the bearings a different size - the basic principles are however much the same.

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Nope, V8 100A versions don't fit on Tdis. The spacing of the 2 lugs (which are in a line) at the front and back is too small to fit over the mount on the Tdi. Rotating the front cover won't change this.

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  • 2 years later...
  • 1 month later...

Hello Guys, 

Excellent topic, but the question now is where did you get the slipring?

I have found the regulator but no way to find the slipring.

Mine is also dead 65Amp, The slipring is not very good so I'm gona change it following this instruction.

Let me know.

Thanks

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