Ducellier 7558B Alternator - Strip Down and Overhaul

Time to refurbish the alternator.

The main job was to change the brushes and check the bearing. I also wanted to see what I could do about the terminals as they were in a very rusty state. Some research showed that the refurbished alternators that you can buy seemed to show lovely clean terminals - so I guessed there would be a way to get at them and replace them.

I'd been waiting for the warmer, drier months as I'd been planning on trying baking soda to clean the alloy body shell. 

Grubby......26 October 2015

I'd already removed the fan blade, bolts and mounting bracket back in 2015 so that I could clean and zinc plate them.

Fan blade, pulley and Mounting Plate Removed - 26 October 2015

Now 2017. With the pulley already removed, disassembly was fairly straightforward. The front end of the casing slid off the spindle. That should have allowed the rotor to be pulled free - but the back 'business end' refused to budge. The end plate has a small plastic plug and I wasn't sure whether this was to lubricate a bearing within, or to use to 'drift' the spindle out.

Cover Over Lubricating Point? 28 May 2017

I took some advice from the CCC Forum and, by part-reassembling the pulley end (without casing), it gave me some leverage against which to persuade the back casing to relinquish it's grip.  With the end cover free, I peered inside, curious to see what was there. No bearing, just a bush - and fairly gummed up with dirt, too.

Bush and Brush at the 'Business End' - 28 May 2017

The brushes were removed.....

Location of Brushes

A Brush.....

Next job was to remove the stator ring. I tried to undo one of the nuts holding the black plastic rectifier cover on and the 'positive' post sheared. You can see how rusted it was. That would need to be fixed..... Removing the plastic cover revealed it was every bit as mucky inside as it was out, with the rectifier clogged up with dirt. That can't be good for conductivity or cooling........

Grubby Rectifier and Soldered Wires - 28 May 2017

Unsoldering the three wires and opening up the clamps, I was able to remove the diode carrier assembly/ rectifier. This also enabled me to pull the stator ring off the rear casing.

Removing the rectifier enabled me to get at the terminals on the casing and - importantly - to replace that broken post. There are a range of different sized bolts and washers used for the terminals but, by digging through various pots and tubs I managed to find equivalents for replacement.

The bolt for the 'negative' post is crimped into the body, but luckily for me, the 'positive' is insulated from the body by sitting in a plastic holder. 

I was able to find a suitable replacement bolt that would fit. 

New Positive Post in Insulator

On the front case I removed the cover and bearing beneath. The bearing looked absolutely fine.

Front bearing Removed

Removing the bearing left the body halves free to clean. I was careful not to blast the passages that hold the brushes as they need to slide in to take-up gradual wear. I was similarly careful to avoid the bush on the rear end as i did not want any burrs or rough spots. Soda blasting leave parts dusty, so I gave them a good wash and dried them with compressed air. I was really pleased with how well the soda blasting worked. The parts came up really clean and without any obvious signs of damage to the detail. (SEE FOOTNOTE AT END).

Clean Body. Crimped Negative Post (bottom LHS) and Hole for Positive Post

I cleaned up and gave the stator assembly on the rotor a fresh coat of green paint as it was peeling in several places. One of the stator wires broke where it had been slotted down into the 'comb' (cooling fins) of the diode carrier so I soldered a new length on.

One thing I didn't do was replace the slip ring. One track was significantly more worn than the other and the slip ring really needed replacing. I couldn't find reference for a replacement intended for a Dueller 7558, and so trying to take measurements as best I could I looked for a near equivalent. I drew a blank and removing mine to get a better idea of shape and measurements would have meant destroying it. I left well alone. Perhaps this is a job I will come back to. As consolation I gently rubbed the rotor shaft down with some very fine wet and dry to remove any burrs  - though there was nothing obvious. 

One Worn Track on the Slip Ring

I carefully dismantled the rectifier, laying out all the pieces and diodes in order.  Everything was cleaned, including each diode. The two alloy 'combs' were soda blasted. 

Rectifier Pieces

Four 'washers' inside each Diode Cradle

The rectifier was re-assembled. Somewhere along the line I got confused and muddled the diodes up! Exactly what I didn't want to do! They all looked the same: one flat side and one 'nipple' side. All the same colour. I did a bit of Googling......

"There are always 6 main diodes, which are often arranged in two groups of three. Diodes within the groups are identical but the group connected to the negative terminal is likely to be assembled from diodes whose body is their anode connection. This is simply for the convenience of being able to bolt all three to the same heat sink. Diodes connected to the positive terminal have the reverse configuration".

Ah. That explained it....... The larger flat sides go against the finned heat sinks, but to maintain current polarity, one set have to be a 'reverse set'. I used a volt meter to test which was the positive side of each and, based on the way they needed to fit back in the assembly, paired them back up together. The Volt meter also suggested that none of the diodes were blown as they only allowed current to pass in one direction. We shall see......

Re-assmbling the Rectifier.....

I began the major re-assembly. All the parts were laid out ready.

Ducellier 7558B Alternator - Main Components

Terminal bolts were replaced. Greasing the bush, I reassembled the rotor and stator loosely on the back end. I was then able to slide the rectifier over the 'positive' and 'negative' posts.

The front bearing was replaced with it's cover and the front end then slotted over the rotor. The whole thing was loosely reassembled with its three bolts and nuts. I made sure that the rotor spun freely on it's bearings and did not catch the stator ring. When I was happy, iItighten the body back up. 

With the body back together back together and the stator ring correctly located, the brushes were then replaced. I re-soldered the stator wires to the rectifier. The black plastic cover plate and the various nuts and washers on the terminals were then added.......

Shiny New Terminals!

All Shiny

I dug out the mounting bracket.........

Shiny Zinc Mounting Bracket

.......and the fan blade and pulley:

Zinc Fan Blade and Painted Pulley

All done. It just remains to be seen if this alternator still works! 

UPDATE - MAY 2018:
Although I was very happy with the results of my baking soda cleaning, a helpful soul at the 2017 CCC D rally offered a view that soda blasting leaves the surface 'open' and more liable to pick up and hold dirt marks. Vapour blasting was offered as a better alternative as it leaves a 'closed' surface. At that time (May 2017) I hadn't investigated vapour blasting but did eventually use it on my cylinder head with impressive results. To cut a long story short, I dismantled my alternator all over again in May 2018 and had the casing vapour blasted! I re-assembled it again about 12 months to the day after my first attempt. To be honest, it looks just like it did when I soda blasted it. 

The pulley has been added and painted and the whole thing now looks like this:

Pulley Added

After Vapour Blasting - May 2018

Before: grubby......26 October 2015