Rebuilding the Lucas 18ACR alternator

Sorry, the flash was down for much of this rebuild and pics are a bit dark. 

The alternator on my car had been making a whining noise which was obviously coming from the front bearing. I put up with this but  after a while it ceased to function entirely- the ignition warning light simply didnt come on with the ignition and this is generally indicative of a wiring fault inside the alternator.  I decided to strip it and use a rebuild kit to change more than the bearings depending on what horrors I found inside. 

Clearly it would help to know how the alternator is put together but I couldn't find a decent and accessible picture of a Lucas alternator;  most show older versions of the alternator I actually have fitted in my car. The closest is this one which shows several different alternators, but mine (18ACR) is shown as figs 13-21. This is very like the one I have but I think a previous version.

The electrical parts appear the same but there are differences in the bearings and the replacement kits illustrated as assemblies 16 and 17. These kits don't seem to be available any more and I think some of their components are now obsolete following the move towards sealed bearings. The rear bearing kit (16) is shown as a clip, bearing and insulator- although I have the insulator and bearing I don't have a clip- there is a groove in the case perhaps I should have one? The front bearing kit (17) also has multiple components in addition to the bearing, a circlip, oiler and two thrust washers or covers. I have only the circlip and I suspect the other components are not required once a shielded bearing was used in later alternators.

Rebuild kits are comparatively cheap and include regulator, rectifier, brushes and slip ring as well as bearings (but no covers, circlips or oilers).  To do this rebuild you obviously need to remove the alternator (disconnect the battery first) and make a note of how the alternator is mounted, orientation of the mounting bolts and the position of any spacers. To dismantle the alternator you will need a set of BA sockets (Nos 2- 6 will cover all sizes needed) and a 22mm spanner for the pulley nut.

Removing the fan and pulley

Before starting to dismantle the alternator measure the clearance between the bottom of the fan and the case- In my car this was 3mm.

 I released the fan using an old drive belt clamped in a vice to hold it  whilst it the pulley nut was undone with a 22mm spanner

Pulley, nut and spring washer removed.

The key way and fan are then exposed

 Rotate notch to align with key way and remove the fan...

notch aligned with key

 .... showing the spacer beneath

Remove key with a soft drift or lever it out carefully with a screwdriver and tip out the spacer.

Key removed, the spacer then just lifts off.

Disconnecting the electrics

Turning to the other end remove the two BA6 setscrews that hold the plastic cover.

 and lift off the cover revealing the electrics.

In this view you can see the components and their connections beneath. The regulator is the silver box at top centre (pics above and below). The white round structure in the centre is the brush carrier and the two folded metal plates crossing it are the brush bases, I will refer to the upper brush in the picture as brush 1 and the lower as brush 2. Both are held on by two small BA screws but only brush carrier 2 has electrical connections.. The large finned structure at the bottom is the rectifier and the domed metal structures fixed to the alternator case are the diodes. 

There are 3 wires emerging from the regulator box and two from the rectifier. There is also an additional yellow wire emerging from the diode on the lhs in the picture above and attached to brush holder number 2.

Make a note of the connections
Regulator wires are as so: 

Red-attaches to rectifier at the top of the central fin

Yellow- attaches to brush no 2

Black- attaches to base of brush carrier

Then remove the single top-central setscrew holding the regulator in place and tip it forwards out of its holders

Removing the regulator securing setscrew

Tipping the regulator out of its mounts, note connection of black wire to brush-holder securing screw

Pivotting the regulator- again note the connection of the black wire (centre left), also the red wire from the rectifier to the diode top right

Lift the regulator out of the way- at this stage I hadn't removed its wiring connections

Removing the regulator- in this pic I have already detached the three regulator wires including the black

The wires emerging from the rectifier are light and dark pink (red?). The light pink also attaches to brush no 2, sharing its connection with the yellow wire from the regulator. 

Rectifier wires connecting to brush no 2 (light pink) and diode (dark pink) in this picture the regulator yellow wire and the second diode wire are still connected

 Detach all the wires from the brushes  (including the diode yellow wire above) and remove the regulator, but replace the setscrews to hold the brushes in place. 

Regulator removed, detaching the yellow wire from case diode to brush no 2. Rectifier light pink wire already detached from this brush

The darker rectifier wire is connected to the second round diode on the alternator base. Note that it fits through this handy clip on the side of the brush holder.

Dark pink wire passes through this clip on the side of the brush holder.

You can then remove the two larger setscrews retaining the brush carrier and at the same time releasing the black regulator wire if not already removed.

Brush contacts removed, fingers indicate the two setscrews holding the brush carrier

The brush carrier then lifts off to reveal the slip ring beneath, unclip the darker rectifier wire from the side of the brush carrier as you lift.

Removing the brush carrier- unclip the red wire from the body

Looking inside the brush carrier there was a lot of grease and the outer brush was worn substantially lower than the inner. These should be replaced at 0.8cms length which puts this one right on time and could explain my loss of function.

Greasy dirt inside the brush carrier, brushes are very uneven in length.

 I could then unscrew the three long through bolts that hold the two halves of the alternator together- fingers indicate two of them

 The front of the alternator (drive side) can then be pulled off lifting with it the rotor still held in its drive side bearing. The regulator side bearing slips out of the bottom case

Removing the drive side bearing

The spindle has to be pushed out of the drive-side case using a press. Refit the spindle nut flush with the end of the spindle and then support the bottom of the case securely on the rests. I could then press the spindle out of the front section - be ready to catch the rotor as it falls free..

Pressing down on the spindle whilst supporting the alternator drive-side case on the iron rests

Rotor removed- note second spacer that was positioned beneath the bearing

The old bearing is retained by an awkward circlip- it would be better if it had eyes for easy removal but here you see the bearing is now positioned just below and in contact with the circlip. I made the mistake in my first rebuild of thinking that this is the position the bearing needs to be. In fact its not, it has just been pushed down during the pressing to remove the spindle. The circlip isn't there to locate the bearing, but merely to stop it pushing all the way out when you are trying to press out the spindle! If you do refit it in this position you will get excessive end-float in the shaft once assembled.

The process of pressing out the spindle has also pressed the bearing down and it has come to rest against the circlip- but note this is not the position in which it should be refitted. It has to be positioned up against the end of the case when rebuilding

You need to remove the circlip before the bearing can be removed- luckily there is a cutout in the housing where you can lever the
circlip forwards and upwards...


 ...gradually "walking" it out of its groove.

Circlip removed!

The front bearing then just taps out of the case- I found it wasn't held very tightly. It was in a terrible state and once the circlip was removed the shielding fell apart revealing horrible solidified remnants of grease inside. I'm amazed that this had been rotating at all!

I checked the new vs old bearing- most alternators use a shielded 6202 Z2bearing which is a very common size (a few use a 6302). I bought a quality SKF electric motor rated bearing.

Refitting the drive side bearing.

I found the new bearing was actually a loose fit and could be pushed in by hand. This will not do because end float on the alternator is controlled by the bearing position. I therefore refitted it using Loctite retaining compound to fix it in position at the front of the case and then refitted the circlip behind it. The circlip caused me some concern because I had thought it marked the desired final location of the bearing, however I now think that the circlip is not there to locate the bearing or to limit its movement at all, but simply to act as a backstop when pressing the spindle out through the bearing

Bearing pushed down against the face of the case and secured with retaining compound.

Bearing flush against the inside surface of the case.

 Place the spacer (smaller) onto the spindle and position the front case on top

 Use a deep socket (10mm in my case) to cover the spindle and bear on the inner race of the bearing.

10mm deept socket fits just nicely over the spindle

Transfer to the press, supporting the base of the rotor on the iron rests- note; take care that the two rotor wires emerge at the front and back so that they are not compressed between the rests and the stator as you press.

Pressing the front case onto the spindle- the force acts on the bearing inner race not the case so the loctite bond isn't strained.

Before pressing, the fan spacer (larger of the two) stands proud of the spindle. The idea is to press the case down the spindle until the spacer sits just below the keyway.

Before pressing- spacer stands proud of the spindle.

 I pressed a while, stopped, remove the socket and checked position until the spacer sat below and without obstructing the keyway.

Spacer now sits lower on the spindle

Spacer fits below keyway and doesn't obstruct the key

I could then test fit the fan to make sure that it rested on the spacer  and could rotate without interference from the key above or the case beneath. At this stage check the clearance between the fan and case comparing it to the clearance measured before you dismantled the alternator.. 

Make sure the key fits in the keyway without fouling the fan

If you press too far the bearing will jam on the spacer beneath and the spindle will no longer be able to turn in the case. In fact there is a degree of flexibility in pressing this case on and this allows you to control the pulley offset to keep the belt run planar. Keep test  fitting the fan-to-case distance as you press on. If doing this again I think I would put the fan in position and press the spacer down on the bearing through the fan so that I could check the offset as I pressed. Obviously you need to set this according to your car. I went for the distance I had measured which is an offset of 3 mm from the bottom of the fan to the case when the pulley is tight.

Removing the rear bearing

The rear bearing sits above a plastic insulator with a small gap (1-2mm)

 I found that the slip ring  was scored

 The slip ring is connected to the rotor windings by two wires which pass inside the bearing and are soldered to the copper contacts on the slip ring. To remove the bearing the slip ring has to come off so melt the solder connections using a iron powerful enough to do so.

Melting the solder to remove slip ring connections

 Wires released from solder joins. Don't cut them as they are only just long enough and in my opinion already too short!

 The slip ring then just pulls off. It has an internal key way that fits into the shaft of the rotor and a small retaining clip (new one supplied with new slip ring)

Slip ring pulled off- note clip on underside in the square indentation.

 Looking from above- slip ring key way in rotor spindle end and the two unsoldered wires that penetrate through the bearing in grooves along the spindle

I marked the top of the bearing with a scribed line and red sharpie before removing it. Sorry about the pic but it was too shiny for both the flash and the auto focus to cope with. You can just see (maybe) the red line I marked on the shaft.



The bearing is on tight and you will need a puller to get it off- this will need quite narrow hooked ends to slip into the small gap beneath the bearing. I used a windscreen wiper puller- tricky and it nearly broke it, but the bearing came free.

Once the bearing was out the reason the the excess grease was clear- it has only one shield the open side being fitted towards the insulator. This is as Lucas intended although it seems a bit odd to me. I'm going to replace with a sealed bearing.

Refitting the rectifier side bearing

The bearing wasn't in too bad condition and made little noise as it was spun but I opted to change it anyway using a metal-shielded 6202 ZZ C3 bearing form SKF. Here I'm comparing them to make sure they are the same size.

Fairly easy to fit the new bearing. Fold the wires carefully and fully into their grooves and then tap the new bearing over them and down the shaft. I used a deep 10mm socket which bears on the inner ring of the bearing only. I tapped it down until the top reached the scribed marks made as above.

Tapping the new bearing onto the spindle

Poor picture but the wires passing through the bearing are (just) visible.

New bearing in place- poor focus sorry. The wires are visible poking through the bearing and at this stage its advisable to use a meter and check for any possibly shorting between the wires and the spindle in case the insulation was damaged as the bearing went on. Connect a meter across the wire and shaft to check that there is no continuity. 

Changing the slip ring

 I could then fit the new slip ring- I inserted the new clip into its base

New slip ring with clip left, old one right

 ..and pushed it into place on the spindle folding the wires up into contact with the copper plates on the side of the ring.

Slip ring in position- about to solder the wire connections

Its a bit of a pig to solder the wires to the new disc. I found that the solder just wouldn't stick to the copper although it loved the wires. I got it to go eventually and all I can say is that you need to clean the copper and the iron thoroughly or you get gummy black deposits. You then need to use more heat than is comfortable as it seems in danger of melting the ring but eventually I got both attached. 

Connections soldered.

Brush change

I then swapped the brushes, they come attached to their folded metal holders.



Remove the setscrews holding the brackets to the holder

 Unevenly worn brushes are then released.

Old brushes removed- these have worn unevenly and one is on the limit for replacement.

 The new brushes just poke in

and protrude through to the inside of the carrier

 Secure them lightly in place with the setscrews before you make the electrical connections.

Swapping the electrics

At this point its obviously easy to fit a new regulator and you could go on and change the rectifier... in my case I'm hoping that the problem was the worn brushes and the grooved slip ring so I'm not going to change the regulator or rectifier unless I find it still doesn't work! The rectifier has 2 soldered connections so removing and replacing it is a bit of a faff- plus it is heat sensitive and given my poor soldering above I don't want to risk it unless I have to! In my case I could then refit the original regulator  and re-connect all the wiring  I had detached above and snug up the setscrews. I could then refit the back cover and jobs done.