Alternator – Chris Vine – Restoration of NNF 10H

Road legal again …. finally!

Jul 152016

I’d been lucky to have an opportunity to drive an unmolested E-Type while on my recent travels (Sydney in an E-Type) and wanted to return the favour when the Christopher was next back in the UK. Not least because he would be able to give valuable feedback, good or bad, on how the two cars compare.

Crossing the Sydney bridge in an E	Christopher’s original S2 FHC

I had experienced slight gear selection issues with mine when changing from 2nd to 3rd and from 3rd back down to 2nd – something I might cover in a future post. Although these were more due to being used to modern gearboxes and resolved by adopting a more sympathetic technique changing gears.

I had decided to keep reasonably close to the original spec. The most noticeable differences are the EDIS electronic ignition system and the Mangoletsi cable throttle linkage. The EDIS system hasn’t been properly mapped yet so the only real difference between our cars was the throttle linkage.

Christopher’s visit coincided with the car’s trip up to the trimmers to fit the hood. It had been up with Suffolk & Turley for a lot longer than expected and so the only opportunity for a drive was on the day he was returning to Australia.

This would have been fine had the MOT not expired while it was up at the trimmers. It had been there so long I hadn’t had an opportunity to organise a test since getting it back and now the speedo had seized. It might be possible to get away with a broken speedo on a modern car as the MOT tests are all static and the brakes tested on rollers.

However due to the limited slip differential, the E-Type had to be tested out on the road whilst travelling at 20mph. Braking efficiency is measured using a calibrated decelerometer. Therefore it would be glaringly obvious that the speedo wasn’t working. So it was a race against time to get the car road legal before he left. No pressure then!

To make matter worse, I’d noticed the ignition warning light wasn’t going out indicating the battery wasn’t charging. I had a matter of days to resolve both issues and get the car through the MOT. Things weren’t looking too promising, especially when I contacted Speedograph Richfield as the speedo hadn’t turned up as expected. I had specifically asked for a 24 hour delivery but they had forgotten, sending it out 2nd class and without the ability to track it. Aaaaaah …. and relax!

I was more concerned about the charging system since I had modified my alternator to a more modern design. This eliminates the 3AW and 6RA relays so the only two things that could be wrong were the 4TR voltage regulator or the alternator itself.

Modified alternator doesn’t need 3AW and 6RA relays … less to go wrong!	Three additional diodes (trio) have been added to self-energise the field coil

A failed 4TR regulator is fairly easy to diagnose. The unit is simply removed and a jumper lead used to link its connector’s F and – terminals together. Essentially this just puts the full battery voltage across the field winding and removes the feedback loop.

Alternator components

As the alternator starts spinning it’s output voltage increases. Without the feedback, the increased output increases the current in the field coil which, in turn, increases the alternator output voltage.

It would quickly reach a run away situation and burn out the alternator coil. Therefore, as soon as you’ve registered that the output voltage is increasing, you need to immediately switch off the engine.

I had pre-ordered another 4TR unit as a precaution but it wasn’t found to be faulty. It was the alternator. The modifications I’d made to the internal electrics and external wiring give it a ‘soft start’. The voltage across the field winding starts at approx. 1.5v rather than the full 12v battery voltage.

This is because the battery voltage is applied across the ignition warning light bulb (approx. 300 ohms) in series with the field winding (approx. 4 ohms). Hence the lions share of the voltage drop is across the bulb rather than the field winding.

The measured voltage without the engine running was 2.74v which seemed a little high. I incorrectly deduced this would result in an increased current flowing in the field coil, which wouldn’t be a bad thing. Once the engine was started, this voltage only rose to 6.36v rather than the expected 14.4v.

The rotor field coil voltage was higher than the expected 1.5v	With engine running, the field coil voltage should rise to 14.4v

A reduced output typically points to failed diodes in the rectifying bridge. This became my main focus. The bridge needs to be removed from the 3-star stator windings in order to test the diodes. So the alternator had to be taken apart and it revealed some interesting problems.

The AL post’s insulating piece had disintegrated. I wasn’t able to source a new one and had to rebuild it as best I could, with araldite making up for the missing bits! Not ideal but it should do for now.

Pulling the pulley wheel	AL post insulator had disintegrated	Temporary fix – rebuilt with araldite

The original slip rings piece was found to be cracked so I had replaced it when the alternator was rebuilt. The replacement has raised sections between the rings but, as the brushes sit either side of them, I thought nothing of it.

These raised sections had been in contact with the brush holder and had worn a groove in the nylon housing. The slip rings looked clean enough but I gave them quick polish with wire wool.

Difference between slip rings	Signs of rubbing on raised sections	Groove worn in brush housing

My multimeter has a diode checking function so it was easy to check the diodes once the bridge had been removed. My suspicions were that one or more of the additional three diodes I’d added for the alternator modification had failed. They hadn’t and all the diodes were fine.

Removing the rectifying bridge	Diodes can now be tested

The other standard checks were made; the resistances of the rotor field and stator windings and the insulation between the rotor coil & rotor and the stator winding and stator laminations. All were fine … and I was stumped.

The alternator was rebuilt and put back on the car to test but there was no change. The ignition warning light stubbornly refusing to go out. I was getting fairly despondent. It was lunchtime, the alternator was in pieces on the bench yet again, there was no sign of the speedo, the car had no MOT and Christopher was due to turn up first thing the following morning!

For some reason I decided to measure the combined resistance of the rotor field winding and brushes. The rotor winding should be around 4 ohms. With the brushes included, I would have expected something in the order of 5 to 10 ohms (max). It varied between 30-40 ohms depending on the rotational positon of the rotor. This was way too high and would result in a significant reduction in the current in the rotor winding and therefore the output of the alternator.

Slip rings required light sanding	Checking coil to rotor insulation

As a last resort and even though the slip rings had initially been cleaned with wire wool, their surfaces were sanded down with a fine wet and dry sandpaper. The combined resistance dropped to only 7 ohms. The alternator was quickly rebuilt and tested. Eureka – it was working!

I’m fairly sure the cause was due to the slip rings impacting the nylon brush housing. The resulting friction had melted the nylon to form the groove and some of the molten nylon had formed a glaze on the slip rings. The sharp points of the multimeter’s leads would penetrate the glaze to give a false impression of the resistance seen by the brushes.

I was expecting an initial voltage across the field winding of 1.5v rather than the measured at 2.74v. The higher voltage was due to a high combined resistance of the field coil and brushes compared with the 300 ohm bulb.

Refitting the alternator
… for the 4th time!

In total I had removed the alternator, taken it apart, tested each component, rebuilt it and retested it four times to get it working!

It was such a relief to get to the bottom of the problem and things started to look up when the postman arrived clutching the speedo. The garage kindly rescheduled things and its second MOT was passed late in the afternoon.

The following morning Christopher and I headed off for a drive and dropped in on his parents. His father had also had an E-Type years ago so it seemed fitting to vacate my seat so he could also go for a spin.

The feedback on how the two cars compared was positive too. The driving experience was very similar which was pleasing as there’s always a fear a restoration could change things for the worse.

Chris takes his father for a spin

One item that got the thumbs up was the PD Gough exhaust which has a lovely throaty roar from 2,500 rpm.

Something I can thank the administrator of the E-Type forum for as his advice was to stick to the standard cast manifolds, avoid the big bore systems and fit 1.75″ tubes with straight through silencers and straight through resonators.

Finishing engine bay & pre-MOT tasks

Air Filter, Alternator, Exterior Trim, Front Suspension, Fuel Line, MOT, Trim & Body Fittings 2 Responses »

Jun 162015

It feels as though the list of outstanding tasks is getting longer rather than shorter. So they have been prioritised into those required for the MOT and those that can wait. Due to the age of the car the MOT is essentially limited to checking the suspension, fuel/brake lines and lights. However, knowing the person doing the MOT, I’d asked them if they would cast a more critical eye over the whole car.

I’d been having trouble balancing the carbs and, although it’s not part of the MOT, I thought it best to have a second pair of eyes look over them. The front two cylinders are running too lean, even though all three carbs have been set to the standard reference point for tuning. So it will be tuned and the headlights aligned beforehand.

I also have concerns about the fuel flow. Last year the petrol tank had be put in-situ to just to start the engine for the first time. The tank was then removed to be painted and since then I noticed that the fuel flow seems to be rather low. Although I suspect I just hadn’t noticed the problem before.

Testing fuel flow from pump	Comparing the fuel flows per minute: 250ml at front bulkhead in bottle, 2litres at rear bulkhead in jug

The measurements of the amount of fuel pumped in one minute was taken at the rear bulkhead union and then at the other end of the pipe at the union on the front bulkhead. Although it’s not really a valid test, as there wouldn’t be any back pressure at the rear union, it did provide a feel for the drop off in flow – 2 litres per minute measured at the rear bulkhead union and only 250ml per minute at the front bulkhead union.

Suspicion is that it may be due to an air-lock created in the pipes. However advice from the forum suggested that a pump in good working order would have more than enough ummph to purge any air locks. Some further checks will be done to get to the bottom of the problem.

Longacre Camber/Castor Tool

The intention was to set up the suspension geometry myself and so I’d purchased a Longacre electronic camber/castor tool and a Trackace tool for the wheel alignment. The camber/castor tool has three legs which rest against the wheel rim with an accurate inclinometer attached in the centre. However I wasn’t thinking things through and had completely overlooked needing clearance for the central spinners.

The prongs on the legs don’t have the reach so I’ll have to have some made up. Unfortunately the MOT centre no longer has accurate electronic measuring tools for suspension set up. This will have to wait until after the MOT.

For some reason one of the dash indicator tell-tale lights had stopped working and the fault traced to the switches in the indicator stalk. It was easier to take the whole steering column off and investigate further on the bench. A loose back-plate on the switch mechanism had allowed the indicator contact to move about and be bent out of shape. So it was easily rectified.

The clamping bolts on the upper and lower steering column’s UJs had been taken off to aid the removal of the upper column. However, I’d become side-tracked and had not refitted them before attempting to tick off another pre-MOT task … making sure the speedo drive was working.

Needless to say, as I was turning round, after completing a successful straight 40 yard speedo run up the drive, the lower column dropped out of its splines. All steering was lost, blocking a now busy communal drive!
Apart from being stupid, it was a rather timely reminder! The complete suspension parts list was used as a check sheet to ensure every suspension nut and bolt was revisited to make sure everything was correctly torqued.

Mudguards, shields and undertrays
The various mudguards, shields and undertrays aren’t strictly necessary for the MOT. However they were fitted, as the horn relay needs to be mounted on the LH mudguard. John Farrell had produced a good guide to the locations and orientations of the five different types of brackets:

Front frame bracket locations	Five different bracket sizes

The first to be installed was the air in-take shield which is attached to bracket A at the top and B at the bottom. The leading face is also bolted directly to the frame. It’s worth noting that bracket E for the floor undertray needs to be put in place around the frame before the shield is attached. In fact it’s worth putting all the brackets in place before attaching any of the mudguards, shields and undertrays.

A & B brackets for air intake shield	Bracket E for undertray is fitted before in-take shield!

The bracket attachments to the frames are identical on both sides of the car, with the obvious exception of the air in-take shield. The torsion bar shields are attached by three brackets – the rear two have the tab with the bolt holes pointing upwards while the front one points downward. Note: the middle bracket on the LH frame is also used to secure the bottom of the exhaust heat shield.

Alternate rear torsion bar shield & undertray brackets	Shield bracket also attaches bottom edge of exhaust heat shield	Front torsion bar bracket (L) and mudguard bracket (R)

The two floor undertrays are simply bolted in place. Although the right hand undertray has a cut out with a separate cover to provide access to the oil filter.

Left hand undertray	Right hand undertray, without oil filter access panel

There wasn’t any point in completing the fitting the mudguards because they will have to be removed to provide access to set the camber and castor. So at this stage they were only bolted to the sill end panel and attached at the front to a side frame bracket. At least this allowed the horn relay to secured for the MOT. Normally the alternator and aircon (when fitted) relays would also be attached to the LH mudguard, but by modifying the alternator it no longer requires a relay.

LH mudguard temporarily in place just for the MOT	Location of horn relay. Alternator relay isn’t needed

Air Filter
I was regretting not trial fitting the air filter earlier. The new fuel pipe I’d made protruded too far from the face of the toe box, hitting the air filter. Fortunately it was possible to remove a short length from the filter end which resolved the fitting problem but re-introduced all the air bubbles causing the air locks.

It took a while to work out the best method of fitting the air filter element, canister lid and air plenum. Once the canister lid and rubber grommet are in place, there wasn’t sufficient access to pull the grommet up around the lip of the plenum chamber. Eventually I found the best solution was to connect these components off the car and then fit and remove as a single unit.

Filter canister was hitting the fuel pipe	Adjusted fuel pipe now narrowly misses it	Fitting canister lid first didn’t work

Alternator testing
Another task was to ensure the alternator was charging properly when the engine was running at higher revs. The outcome wasn’t as I’d hoped – it wasn’t charging at all, measuring only 12.5 volts! The converted alternator is now self-energising – the AL terminal, normally used for monitoring the alternator output via the ignition warning light, now provides a DC supply to power the field coil. Finding earth via the field coil through the 4TR voltage regulator.

Testing the alternator

The AL terminal was reading zero voltages at idle rather than the expected 14.3 volts! The voltage regulator controls the alternators output to avoid ‘run-away’ where its output would continue increasing until it burnt out the various internal components and/or windings. Increasing the voltage across the field coil increases the alternator output voltage, which in turn increases the field coil voltage.

The 4TR regulator acts as a fast-acting on/off switch. When the output of the alternator increases above a determined voltage (around 14.6v), the regulator switches off the current flowing in the field coil and therefore the alternator voltage drops. Once it has dropped sufficiently, it switches the current in the field coil back on and the alternator output starts to increase, until the cycle repeats.

A passing peacock offered
no helpful advice!!

Suspicion fell naturally on my modifications to the alternator and also the 4TR regulator, which are known to be fragile. A faulty voltage regulator can easily be identified by removing it and using a jumper lead to connect the F and ‘-‘ leads in its connector.

If it is faulty, starting the engine will cause it to start charging (indicated by the alternator output voltage or the battery gauge rising above the battery’s normal 12.3-4 volts) If so, the engine should be switched off immediately and the 4TR unit replaced. It was a great relief to find it was the 4TR unit that was at fault and not my handiwork! A replacement was ordered which confirmed the diagnosis and it is now working as expected.

Crossing fingers
I didn’t want to drill holes in the bodywork for side mirrors and so some clamp on mirrors have been attached to the window frames. That just about completed all the pre-MOT jobs.

Clamp on side mirrors fitted	After all this time, it’s finally ready for the MOT!!

For the first time in several decades, 1R1421 hit the road …… on it’s way to the MOT centre! …. fingers firmly crossed!!

Rebuilding and converting the alternator

Alternator 7 Responses »

Nov 082013

The ‘refresh’ of the alternator turned into a full rebuild because the rotor’s slip ring needed to be replaced, as it was heavily grooved, and the main rotor bearing had seized. In fact, the slip ring was found to be cracked on the underside once it had been removed. Fortunately all the components needed for a rebuild are still readily available.

The wiring diagram for the Rootes Parts Lucas 11AC alternator conversion As previously mentioned, the Rootes Parts website covers the conversion of the internal electrics to a more modern, self-energising design.

The revised electronics energises the rotor field winding from the alternator’s output, rather than directly from the battery. This produces what Rootes term a ‘soft start’. When the car is started, the output from the alternator is zero, so a much reduced current flows through the field winding as it is wired in series with the more resistive Ignition Warning Light bulb.

The initial current in the field coil is approximately 10% of the normal operating current. However as the alternator output increases up to a typical 14.3v to charge the battery, the voltage either side of the warning light becomes equal, effectively removing it from the circuit energising the field winding. As there’s no voltage drop across the warning light, it goes out and the field winding is now powered directly from the 14.3v alternator output.

Being self energising also has the added benefit that if the belt fails, the alternator output would fall to zero and the field winding current reduces back to 10% of the normal operating current. Thus avoiding the field winding being burnt out.

The slip ring plate needed to be replaced but first needed the field wire connections un-soldered Three screws fix the split ring plate to the rotor. Once removed, the plate can be pulled away from the rotor to reveal the ends of the rotor field winding, which pass through the rear of the slip ring plate and are then soldered at the front to the brass slip rings.

It took a high output soldering iron to melt the solder joints, probably due to the age of the solder, enabling the slip ring plate to be removed.

The rotor’s field winding wire is insulated by an enamel coating and then covered by a fibreglass tape so these were protected by masking tape before the rotor was bead blasted, in preparation for painting. The rotor was painted in numerous coats of Burnt Copper and then Clear VHT Engine Enamel paint. VHT paint was chosen due to the high operating temperatures reached and the proximity of the alternator to the exhaust manifolds.

Painted in Burnt copper VHT	Curing in the oven	Winding re-lacquered

Once the paint had dried, it was cured in the oven at around 100 degrees Celsius for about 45 minutes ….. and, rather sheepishly, the oven then left for a day or two until the aroma had gone! The fibreglass insulation sheaths covering the ends of the field winding had deteriorated and eventually broken free with all the disruption getting the slip ring plate off.

I found an electronics supplier, Brocott UK, who supply the 2mm fibreglass sheathing as well as bottles of motor winding enamel and new fibreglass tape. After the old tape was removed and the winding cleaned up, it was re-coated with a generous coating of enamel. The new sheathing had to be held in place by a small amount of Araldite were it enters the rotor as I needed to ensure the field windings couldn’t short against the rotor body.

The field winding was re-taped which was a fairly fiddly job, as the 8 prongs of the rotor get in the way. I suspect the winding was originally wound and taped before the two halves of the rotor were fitted together. Before progressing any further, two important tests were made; i) the winding resistance and ii) confirming the field winding wasn’t shorting with the rotor. The winding resistance was 4.2 ohms which is slightly above the recommended upper limit of 4 ohms but I’m happy to leave as is.

Checking the winding wasn’t shorting	New slip ring soldered and fitted

Attention now turned to the fitting of the main rotor bearing. The original had seized and so a replacement bearing kit was ordered. The new bearings are sealed for life units which have a slightly lower maximum RPM. However I was assured they would be fine unless driving at full RPM for prolonged periods.

The outer cover plate and then the rubber ‘O’ ring are placed in the front alternator housing before the bearing is tapped into place. Finally the rear cover plate is inserted and the whole ensemble retained in place by a circlip. I couldn’t compress the parts sufficiently to fit the circlip, due to the thickness of the new rubber ‘O’ ring, and had to resort to clamping them between two suitably sized washers using a bolt. With the bearing installed, the rotor was tapped into the bearing with a nylon hammer.

Parts of new bearing kit	Compressing the ‘O’ ring	Rotor press fitted into bearing

It was only at this point that I found a spacer that is clamped between the inner bearing race and the fan & pulley did not fit. The inner diameter of the new bearing cover was too small to enable the spacer to be fitted. So the whole bearing had to be removed and re-fitted using the original outer cover!

Alternator’s internal electronics
The stator's three field coils attached the stator to the rectifying diode housing The rectifying diode housing and attached stator were removed from the rear housing by undoing the external nuts on the three terminal posts. Once again I had great trouble de-soldering the joints, this time connecting the stator windings to the diode housing.

The problem is that typical soldering irons, used in electronics, don’t have sufficient output to melt the solder. This is mainly because the relatively large gauged wire used dissipates more heat than the soldering iron can deliver and the diode housing is designed to act as a heatsink.

So I’m now the proud owner of 4 soldering irons, with increasingly higher output ratings! The highest being an 80W iron normally used for soldering stained glass window frames – it was ideal!

The Lucas 11AC alternators use a three-phase bridge rectifier, containing two sets of three diodes, to convert the AC output from each of the three stator windings into DC. Essentially the output of this type of rectifier is close to a DC supply as it is the sum of the positive components of the three AC voltages, which are 120 degrees out of phase from each other.

The conversion involves adding a further set of three diodes to provide an additional DC output to power the rotor field winding. The self-energising alternator no longer requires a 3AW relay so the AL terminal can be re-used for the secondary DC output.

Each terminal post has a variety of insulations and metal fittings – their fitting order was carefully noted as each part was removed to ensure they were correctly refitted during the rebuild, as shown in the photo below.

Notes taken during disassembly	Parts assembled for the conversion

The main points to note are the B+ and AL terminal posts must not short with each other or the alternator casing. With this in mind, the order and purpose of insulators becomes more obvious. The diode housing consists of two halves into each is pressed a set of three diodes. The two halves also act as part of the circuitry as well as a heatsink.

The left hand side is connected directly to the alternator housing via the Earth terminal and provides the common anode connection for the three (negative) diodes. Similarly the right hand side provides the common cathode connection for the three (positive) diodes, which is the B+ output.

The original AL terminal is connected to the wire connecting a pair of the rectifying diodes. This will be replaced during the conversion so the AL terminal is then connected to the output of the three new diodes.

Although the six button diodes look identical, the outer casing acts as the anode for the three inserted into the left hand heatsink (their cathodes being wired to the stator coils) while it acts as the cathode for the other three. Therefore it is essential to ensure they are installed into the correct side of the diode housing. Fortunately most multimeters have a diode test function so it’s easy to check which is which.

The same 2mm glassfibre sheathing for the rotor winding was used to insulate the 16swg copper wire connecting pairs of diodes on each half of the diode housing. Again, the 80w iron made the soldering a doddle. The next step was to install the additional three 6 amp diodes to provide the output for the field winding.

Their anodes are soldered to the anode posts of the positive diodes, delivering the B+ output, and their cathodes are all connected to the AL post. I crimped and then soldered the cathode wires into a 3/16″ eyelet terminal which fits neatly onto the AL post.

Wiring of the standard rectifying diodes	Additional diodes to power field winding

There’s not a lot of room between the rectifying diode housing and the rear alternator body so insulation was added to the leads of the additional diodes. Several trial fittings were made to ensure the diode housing did not foul within the alternator body, before finally soldering the diodes in place.

In the meantime the resistance of the stator coils had been checked to ensure all was well before the stator was cleaned up – wire brushing to remove all the rust and then repainting. The stator was then reattached to the diode housing by soldering the coil field wires.

The bearing kit came with both front and rear bearing so the latter was pressed into place and the bearing completed by fitting a felt washer followed by a metal washer and finally a square, spring washer. The corners of the spring washer lock against the alternator housing and hold the other washers in place.

Rear bearing components	Housing alignment markings

Two things I wasn’t sure about was whether to soak the felt washers in oil and what grease to use for the bearing. In the end I soaked the washer and opted for a polyurea grease. Hopefully it should be ok! The stator and diode housing could then be refitted to the rear alternator body, taking care to add the various insulating washers.

New slip ring brushes were fitted before reuniting the two halves of the alternator. The two alloy halves have a small dimple marking which both need to be aligned with the narrower and deeper groove in the stator.

The rebuild was completed by fitting the spacer on the rotor shaft followed by the Woodruff key, the cooling fan and finally the pulley.

Electrical terminals at rear	Front & rear halves reunited

The only decision left is whether to get the alternator professionally tested off the car or wait until the engine is running …..

Dismantling a Lucas 11AC alternator

Alternator No Responses »

Mar 202012

My initial plan for the renovation of the alternator was mainly cosmetic but also to check, and replace where necessary, the slip rings and brushes. Slip ring wear can be determined by removing the brush holder and they had definitely seen better days. They were quite heavily grooved so the renovation soon turned into a full rebuild. At this point I started to research the workings of the Lucas 11AC alternator to help understand what I was taking on. I came across the Rootes website which covers an upgrade of the internals to a more modern design.

The upgrade involves adding an additional three rectifying diodes, the output of which will be used to energise the field coil. The main benefits would be that by changing to be self-energising, the rotor winding wouldn’t be susceptible to burn out in the event of the alternator belt failing, there’s no need for the alternator relay or 3AW ignition light relay and it provides a “softer” start, therefore providing better protection for the other electrical components.

Unfortunately I had destroyed the 3AW relay when the car was dismantled – one of its spade connections was more strongly attached to the female connector on the wiring loom than the relay itself and broke free! I’d also read that some viewed the relay as a weak point in the charging system and prone to failure, although modern solid state units are available.

It made sense to make this upgrade while the alternator was dismantled and would avoid needing to source a new 3AW unit. The upgrade didn’t appear to be too complex and hopefully within my DIY skills!

The diagram is for a positive earth alternator but does reflect the interior component for negative earth models

The main components of the Lucas 11AC alternator are; the alloy drive end bracket, the rotor, the stator laminations & windings, the rectifying diode heatsink and the alloy slip-ring end bracket. The diode heatsink is attached to the rear casing via three insulated threaded studs, which act as the electrical terminals. The stator is clamped between the two end brackets with the rotor passing through the middle.

The dismantling of the alternator proved to be much harder than the other electrical components. This was because the design uses a woodruff key which, despite all efforts, was refusing to come out. The woodruff key is a semi-circular disk that is inserted into a slot in the alternator shaft, leaving a protruding tab. This tab mates with key slots in the belt pulley and cooling fan to prevent them from rotating relative to the shaft. The pulley and fan are held in place by a retaining shaft nut and can be withdrawn, once the nut has been removed, to reveal the key.

A slot in the pulley mates with the protruding woodruff key

With the end nut removed, the pulley and fan can be removed

The woodruff key is then revealed - on the left hand sie of the shaft

The difficulty in removing the key was that it did not protrude enough to enable a drift to get onto the end of the key with a sufficient angle away from the shaft. After many frustrating hours getting nowhere, I decided to do some research on the internet in the hope that I would find useful tips on how to remove them. After many frustrating hours surfing the internet and getting nowhere, except for pearls of wisdom as useful as a chocolate teapot (“then remove the key with pliers”), I left it for several days to have a re-think.

In the meantime the rest of the alternator was dismantled by removing the three clamping bolts holding the unit together. This enabled the alternator to be split in half; the front drive end bracket & rotor and the rear slip ring end bracket with the attached rectifying diode heatsink and stator.

Complete unit prior to dismantling

Rear slip-ring end bracket with the rectifying diode heatsink and stator

View of rectifying diode heatsink which houses the six button diodes

As mentioned, the diode heatsink is attached to the rear casing via three threaded terminal posts. Once the external retaining nuts have been removed from the terminals, the stator and diodes heatsink can be withdrawn. The two are connected by the wires for the three stator windings.

Care was taken to note the various insulating washers and fittings on the terminal posts. Both the B+ and AL posts are insulated from the slip ring end bracket while the third terminal post acts as the negative earth connection. The plastic housing holding the sprung slip ring brushes was removed, followed by pressing out the rotor shaft bearing from the rear casing.

Electrical connections at the rear of the alternator

Removing the plastic housing cover reveals the rotor brushes, which can then be withdrawn

Stator and stator winding, with the diode housing attached

I could put it off no longer – the woodruff key had to be removed. The solution that finally worked was very Heath Robinson, essentially using a vice to press the bottom of the key into the shaft. This caused the key to rotate in the slot resulting in pushing the upper part ever so slightly outwards but enough to get a drift onto it. It still required a reasonable amount of force to drift it out but at least I could now continue.

Now the key had been removed the rotor and front casing could be separated. All that remained was to remove a circlip holding in the front rotor bearing so it could be pressed out. The bearing had almost seized solid and couldn’t be rotated by hand so I was glad I had decided to overhaul the whole unit. The two end casings were then sent away for ultrasonic cleaning while parts were sourced for the upgrade/rebuild.

The commutator was showing signs of wear so it was removed. Replacements are still available

Grooves had started to form in the commutator where the brushes make contact

Finally the front rotor bearing was removed