Repairing the Magnette clock

Details

Written by Colin Goldsworthy

Anybody who is into any English classic car built in the thirty years after the war which sported a clock will know one thing - nowadays most of them don’t work. Even cars that have had expensive restorations often have just one thing that lets them down - the clock doesn’t actually do anything. These days I believe you can get electronic movements which will get them going again (I’ve never seen one) or you can settle for your clock hands remaining motionless as long as the face, hands and bezel are in nice condition. But if, like me, you really would like your clock to work again with its original mechanism the good news is that it can be done. Over 40 years I have owned among others eight ZB Magnettes and three Wolseley 15/50s all of which had a clock which I was able to bring back to life. Of course at the beginning it was a voyage of discovery with various components ending up in the bin and having to be replaced but the mechanism is now like an old friend and I have been asked to write this to encourage others to have a go. This article together with some photos explains the mechanism, what goes wrong with it (there is just one weakness in the design and it is always this that causes it to stop working), how to take it apart, repair it and put it back together again. And it may not cost you anything either as nothing may need replacing, just several (maybe quite a few) hours of careful, and at some points, delicate work but with a real sense of achievement when it starts up again with a lovely ticking sound which I imagine the modern electronic unit can’t give you. My aim has been to produce a piece which provides fullest details to enable someone who has never even seen one of these clock movements before to tackle it successfully but it does mean that the article is very long I’m afraid. Hopefully all of the questions that may arise as you work on it will be answered. I dismantled and worked on a Magnette clock as I was writing this to try and make sure I didn’t overlook anything.

INTRODUCTION

A few general points before getting down to detail. The original mechanism in these clocks is fascinating and ingenious containing many precision engineered parts, some very small. The job involves slow methodical and delicate work. What you are working on is not a car job at all in the usual sense but the upside is that this is a job you can carry out in the depths of winter in the comfort of your own home – no dirt or oil or mess, just lots of fascinating little parts to dismantle and put back together (in some cases very little dismantling at all) and, as already mentioned, there will be just one part of the mechanism that requires attention, and it will always be this that causes the clock to stop, so no fault diagnosis will be required.

You will need good light - when the light is poor I use a desk lamp with a bendy stalk and a 100W daylight (blue )bulb - a small pot or two for dropping little bits in (if you don’t you will lose some!) and for tools, all that is required are some precision (watchmakers) screwdrivers with flat blades in good condition (no crossheads are needed) ranging from ½mm or less (this will be your main tool) through 1, 1½, 2mm plus possibly a few other smallish screwdrivers of varying sizes, some small pointed and flat nosed pliers, some clean thin cotton cloth and some light machine oil. One “luxury” I use (not essential as the flat nosed pliers will do the job) is a Stanley “Screwdriver” handle with a ¼ inch socket end and a 3/16 socket for undoing the four main nuts inside on the back of the movement. I also bought a pair of “off the shelf” reading glasses in Boots with the maximum magnification on offer (x3) which were fine for me for the close up work the job entails. Finally you will need an old car battery to put it on test at various times as you go along. The battery doesn’t need much life in it to operate the clock which incidentally is the reason the mechanism was devised the way it is as the current drain is so small. If the precision tiny parts sound daunting don’t be put off. You just need to keep remembering to take it all carefully and gently.

Virtually every clock fitted to a British car for thirty years after the war was made by Smiths Industries - some for more upmarket vehicles like our Magnette were branded as Jaeger. Although they all looked different and later clocks had the timekeeping screw and hand setting controls on the front of the casing necessitating a few minor changes inside, the three main components of the movement which are the balance wheel assembly, the spring contact assembly and the coil (plus most of the gears) were identical in all of them because, being precision engineered parts, they were expensive to manufacture and the cost of altering them would have been prohibitive and pointless. If you are going to need any replacement parts it will only be the first two items mentioned – I have never needed to replace the coil. It follows therefore that any Smiths/Jaeger clock you can get hold of made anytime in those decades (identified by 4 screws on the back securing the clock mechanism to the casing) will have identical main components to the Magnette unit and can be used to repair yours. You take your chances of course on whether the crucial parts will be any better than your own but they could well be for reasons I will explain further down.

So with all that by way of introduction off we go.

TAKING IT APART

I will leave the description of how it works until you have reached the point where you are holding the movement in your hand. After removing the clock from the car as per the workshop manual instructions first unscrew the knob which sets the hands and starts the clock (just grip the hexagon on its shaft with your pliers and loosen it.) Hold the clock upright as you unscrew it as there is a loose fitting spring washer which may drop off inside (can be retrieved later if it does). Before tackling the clock proper I always renovate the little box made of thin grey card surrounding the illumination bulb holder on the top of the front casing which invariably has suffered hardening and cracking due to heat from the bulb. If you are lucky most of it will be intact but often bits have broken off or gaps opened up through which the light escapes. Don’t be tempted to bend it as bits will break off. Fill in any openings (or make a new box) and seal the open edges with PVC tape or similar (don’t cover the two heat ventilation holes at the back) so no stray light will show through the headlining. Note that directly under this box is a strip of transparent plastic stuck to the front casing covering the top slot which I think was there to stop heat from the bulb burning the green plastic below it. Over the years this strip discolours and reduces the light reaching the clockface so I always remove it (the green plastic has never burnt but the light is better and “greener” on the clockface.) Another little tip for maximising the illumination is when replacing the bulb before refitting the clock make sure it is turned in its holder so the bulb filament is horizontal - ie parallel with the top of the casing not at an angle so there is a maximum spread of light from the filament.

There is a procedure for removing the front casing from the main casing to prevent damage because if the glass is allowed to come out with the front casing, as it will want to do, it will also pull the clockface out as well (over the years the glass will have stuck to the face at its four corners by the rubber buffers fitted there). This will in turn bend and pull the hands off their spindles. To remove the front casing you will see four ears on it, two at the top and two at the bottom, which may or may not be bent down to press against the main case to hold it in place and also to make an earth return to the main casing for the illumination bulb. This was a poor idea and on later Magnette clocks the ears were left straight and the front casing is held in place by two grub screws one on each side. So either bend up the ears or remove the screws (the first little parts for your storage box!) Now with a finger against the glass to keep it in place manoeuvre the front casing off together with the green plastic surround. Remove and discard the strip on the top of the casing. Then unstick the glass at its four corners and remove without lifting the clockface. Now remove the hands. The best way is with two small screwdrivers placed under opposite sides of the hands (minute hand first). Carefully prise them off with equal pressure both sides but not without first placing a cloth or similar over it as it may ping off. Without something to prevent it flying anywhere you may never see it again no matter how hard you look! (I’ve been there). With both hands removed the clockface can now be dropped out and you have your first sight of the movement inside.

Turning to the back of the casing, loosen the tiny grub screw in the timekeeping lever and prise it off noting its position on the scale before doing so and also which side of the lever the grub screw is situated so as to refit it the right way round. Most of these clocks seem to keep the right time with the lever one or two segments on the scale towards the right of the central position (fast). Incidentally if you have need to move the arm inside the movement that moves around the hairspring to alter the timekeeping (you’ll see this when you finally get it out) it will need resetting correctly in relation to the lever you have just removed. With the inside arm pointing straight up, the lever on the back of the casing should be in the mid position between Slow and Fast. Next remove the grub screw securing the earth strap to the centre of one of the four securing screws on the back, loosen the screw at the other end of the strap where it attaches to the case and move it to one side. The four securing screws must now be removed. I have sometimes hit a little snag with these down the years but it is not difficult to overcome once I realised what was happening. Looking inside the case from the front you will see four main brass nuts on the back of the movement. The screws on the back of the casing screw into these. But looking inside you will also see between these nuts and the casing a grey alloy back plate (the knob which turns the hands screws into this) which clips onto the ends of the brass nuts.

Sometimes as the outside screws are undone one or more of the nuts inside unscrew with them off their pillars but the movement will not come out even if the nut(s) inside come fully undone because of this backplate which is clipped on to the end of the nuts. If this happens you need to prevent the nut inside turning (a screwdriver pressed against it using the inside of the case as a lever or a pair of angled end fine nosed pliers etc will do it) and then withdraw the four screws from the back of the casing. This only happens because it may be the first time the clock has been dismantled since the car was new. To avoid a repetition, should you ever need to take it apart again, make sure when refitting that the brass nuts are done up tighter on their pillars than the outside screws which go into them! Now push the rubber grommet on the back through which the feed wire runs into the inside of the casing (if you pull it outside it may not go over the bullet connector without splitting) and withdraw the movement. The grey alloy backplate should now be removed but before doing so, screw the knob that moves the hands back into it (with its spring washer for spacing reasons) and push it up and turn it as you would normally when it is on the car. You will observe two things, first the cogs engaging that turn the hands but also note how a phosphor bronze spring strip is pushed up and makes contact with a pin that runs through to the front plate. I will call this the earth pin and will be referring to it a number of times. When the strip touches the pin the circuit is made live and sets the clock going. Unscrew the knob again and remove the grey plate. It will need prising off as the ends of the nuts which fit through it have flared ends so it won’t just drop off. It won’t get damaged if it’s not pulled off totally squarely – it can be prised up at whatever corner wants to go first.

Now is a good time to stop for a cup of tea and study it for a while. The more you look the more you realise just how many finely engineered parts there are. The part you will have taken in first is the balance wheel with a hairspring attached - just like any normal clock escapement. But the rest is rather different. With your finger, lightly flick the balance wheel and watch what happens as it rotates back and forth. You can pass current through it and see if it wants to go on its own. It may try but will struggle and give up. It is immaterial if your wire from the battery to the feed wire comes from the positive or negative terminal (these clocks work ok on either positive or negative earth). Your other wire from the battery I usually hold against one of the brass nuts.

HOW DOES IT WORK ?

Below the balance wheel is a coil comprising thousands of turns of very fine copper wire with a metal arm projecting from each end which reach up to the edge of the balance wheel. When current passes through the coil the two arms become electromagnets. The balance wheel itself is made of non-ferrous metal (ie incapable of being attracted by a magnet) but bonded to it is a piece of ferrous metal set at three equidistant points around the wheel. When the coil is energised the arms exert a pull on the ferrous parts of the wheel to pull it round against the action of the hairspring. But the current is being continuously switched on and off twice every second. As you were flicking the balance wheel you would have seen a pin attached to the wheel near its centre brushing past a spring contact in both directions comprising two turns of a phosphor bronze spring (like a rudimentary hairspring) to which is attached at its tip a tiny piece of hardened steel about a millimetre in length (or at least it was when new.) It’s not easy to notice but this spring which moves on a pivot pin continues downwards and is fixed to the earth pin. 

As the pin on the balance wheel brushes back and forth over the hardened steel tip of the spring contact the circuit is completed and the coil energised and de-energised twice per second which combined with the pull of the balance wheel’s hairspring causes it to rotate back and forth. The last clever bit is a cam arrangement on the balance wheel spindle which actuates against a wheel with spaced cup shaped teeth which turns as the cam rotates back and forth and this drives the hands through a chain of worm gears and cogs. The thin black strip that presses against the top of the cupped tooth wheel spindle applies gentle tension to stop the wheel moving slightly between each push of the cam as if this happens they can jam up. So the balance wheel as well as being the means of adjusting the timekeeping (you will note the moveable arm fitted over the outer coil of the hairspring ) also drives the clock. There is no motor. Clever isn’t it! The seven photos below show various parts of the movement in situ but without other parts so they can be seen more clearly. Photo 1 shows the back of the clock with the coil and the electromagnet arms surrounding the balance wheel. Photo 2 shows the balance wheel and cam and the toothed wheel against which it operates. The pin on the balance wheel can just be seen but the spring contact has been removed in this picture. Photo 3 is of the balance wheel and clearly shows the pin and the spring contact. Photo 4 shows fully the spring contact/earth pin assembly while photo 5 shows the balance wheel assembly sitting on the T shaped bracket. This picture clearly shows the wear that can take place on the pin where it has been brushing the spring contact. Photo 6 shows the individual parts that secure the spring contact/earth pin assembly and its pivot pin to the front plate while Photo 7 is of the gear train from the cam driven toothed wheel through to the spindles that turn the hands.

THE ELECTRIC CIRCUIT

The live feed is simple. You will see the feed wire is connected to a terminal from where a wire runs to the coil. The earth return is not so obvious. The earth return wire coming back from the coil is attached to the earth pin to which the spring contact is fixed. This earth pin and the pin on which the spring contact pivots are both secured to the front plate but are electrically insulated from it (you will see the brown mica insulation on both sides of the front plate - more on this later). The earth return is via the earth pin, through the spring contact to the pin on the balance wheel, through the wheel itself to its hairspring which is fixed to the T shaped bracket on the back (current can’t flow via the balance wheel spindle as it runs in jewelled bearings) and thence via the brass nuts to the outside fixing screws one of which has an earth strap to the casing as the screws are mounted in rubber to absorb shocks.

WHY DO THEY STOP WORKING?

Clever and beautifully engineered though it is, there is unfortunately one flaw in the design and it will be this and only this that is the reason why all these clocks after a relatively short life start to run erratically and then stop. It lies in the pin on the balance wheel and the spring contact (photo 3). As already noted, these make and break the current twice every second and as the clock is the only piece of electrical equipment on our cars that would have run 24/7 these little bits brush past each other an incredible 63 million times a year! Over time (and I think it only took two or three years when they were new) the pin and contact wear and also get dirty causing arcing so also burn away. On later clocks Smiths added a condenser fitted to the feed wire terminal to reduce this which, incidentally, I’ve only ever seen for use on positive earth vehicles. If you use one of these and your car has been converted to negative earth the condenser will blow instantly although the functioning of the clock won’t be affected. The pin wears where the spring contact’s metal tip has been making contact, (see photo 5) sometimes so much that half the pin breaks off and the metal tip of the spring contact can also wear away to half its size or almost vanish. One other issue associated with the spring contact which will not be readily apparent is that over time it can get permanently deflected out of line with its correct position when at rest which should be pointing straight at the balance wheel spindle. This means it is having to be deflected by the pin more in one direction than the other as it brushes over it which will make it run erratically or stop. It is very delicate and has to be just right to work properly. Further down I’ll explain how to recentre the contact which requires a bit of dismantling. In every case these will be the bits you have to attend to if you want your clock to go again and once you’ve done it, fitting an on/off switch under the dash or disconnecting the battery so it only runs when you use your car should mean troublefree service for a long time.

You may be thinking that with this design flaw won’t my clock and any I buy for spares all be unserviceable ? Well actually no. They really do all vary and I’ve had at least 30 through my hands. Some clocks stopped running early in their life and if the owner has disconnected the live feed and it has never been reconnected the condition of the pin and contact can be quite good and serviceable after cleaning and adjusting the position of the contact against the pin to compensate for wear and no dismantling will be required. Even if the clock has never been disconnected, as long as the pin and contact have not been touching each other much or are so dirty so as to inhibit current flow, they may be good enough to reuse. But if they have been permanently arcing they will have burnt away and will need replacing. I suspect that most owners, like myself years ago, may not realise that though the clock has stopped working nothing has actually burnt out and it could have stopped in such a way as to be permanently draining more current from the battery than it did when it was going!

GETTING YOUR CLOCK WORKING AGAIN

Firstly examine closely the state of the balance wheel pin and the steel tip on the spring contact. Depending on what you find will determine what you have to do. There’s no reason, of course, why you shouldn’t connect it up to your battery and see if it works. If you flick the wheel it may struggle to start and then stop (this will confirm that the coil is ok although in my experience I have never come across one that has burnt out). If the full length of the balance wheel pin is still intact, even though part of it may have worn away where it has been brushing the contact, (photo 5) and there is at least ½mm of the contact’s metal tip left (it was about 1mm when new) then the good news is that you should be able to get it going again without having to replace any parts. Nor will any dismantling be required unless the contact needs recentering (how to do this is explained later). The pin and contact will just need cleaning and the contact resetting in relation to the pin. I’ll deal with this scenario first. The first thing is to clean the pin and the contact. This may look daunting as the parts are so tiny and as they both move freely, neither can be properly cleaned without holding them in various fixed positions. The method I have come up with is as follows. To clean the pin, I rotate the balance wheel with a finger and hold it in various positions (it won’t damage the hairspring to move it round beyond its normal operating range which is a bit less than ¼ turn each way from centre). I clean it around its whole circumference by gentle scraping with a tiny (½mm blade) screwdriver. You could also try a tiny bit of kitchen roll on the end of the driver wetted with methylated spirit, but it is all so delicate I just do it dry with my fine screwdriver. It must be done very carefully because if part of the pin is well worn where it has been making contact it may break off at this point and experience has shown me that the bit that is left will not be enough to reposition the contact on the pin as it will be too close to the wheel. If this happens, a replacement balance wheel, hairspring and spindle assembly will be needed but it is not difficult to fit – more on this later.

For the spring contact the tiny metal tip is the only part of it that needs cleaning. To clean the side that faces up I turn and hold the balance wheel with my finger so the pin is underneath the contact and touching it to act as a support. If part of the tip is burnt away and as you have not yet made any adjustment it may slip past the pin. If so, carefully move the contact tip closer to the pin a fraction by gently pushing the tip from behind. The U shaped part of the contact will bend to allow for adjusting its position. Holding the pin in position with a finger on the balance wheel gently scrape the tip with your fine screwdriver until it is shiny again. This takes very little time. To clean the underside of it, pull the contact round with a tiny screwdriver anticlockwise (with the front of the movement facing towards you) against the action of its phosphor bronze coil spring (this will not stress or alter its tension) and hold it against the main pillar which joins the front and back plates together. You can now scrape the underside of the tip with another fine screwdriver until this is also shiny. At this stage I also apply Everyman light machine oil with the tip of the screwdriver to the cam and cupped tooth wheel and the ends of its spindle, (photo 2), the two worm drives on the gear train and their spindle tips (photo 7) and the pivot pin for the spring contact shown in photo 4 and the “exploded” picture photo 6, (not on the contact and pin itself of course). To oil the spring contact’s pivot pin in the centre of the phosphor bronze coil move the spring coil along the pin by pushing very gently on its centre bit - the balance wheel will stop you pushing it right off. Although the spring coil is straight where it runs down to its fixing point on the earth spindle, moving it sideways a bit won’t twist or damage it. Apply a tiny amount of oil with the tip of your screwdriver then move the spring coil back fully on to its pin. The jewelled bearings for the balance wheel spindle don’t need oiling neither do the cogs on the front plate which drive the clock hands.

ADJUSTING THE CONTACT

You can, of course, run live tests at any stage of proceedings to see whether it wants to go and further down I outline the tests that will tell you for sure if you’ve done it and it will keep going when back on the car. You never know if bending the contact forward slightly so the pin could act as its support while you cleaned it might have set it up just right! But assuming it hasn’t proceed as follows. As already mentioned, part of the pin and contact tip will almost certainly have worn or burnt away and adjustment must be made to bring them back into the same relative positions as when they were new. The position of the contact relative to the pin is crucial and is the heart of the whole job. Whilst maintaining a 90º degree angle of the contact to the pin it must be reset at the right distance from the pin. What do I mean by this? Think about how the balance wheel is made to rotate back and forth. If the pin just brushes the very end of the contact tip because the contact hasn’t been set close enough to compensate for its wear, the wheel will only rotate a small amount each way before ceasing to touch it thus cutting the current to the coil and stopping the pull of the electromagnetic arms too soon. Although the balance wheel may be reciprocating enough to actuate the cam to rotate the cupped toothed wheel leading you to think it’s been fixed, because it is not moving enough in either direction it will not keep going. If on the other hand the contact tip is too close to the pin it will take more effort for the pin to brush over it as the contact will have to be deflected against the tension of its hairspring by a greater amount than the design parameters so this will also make it stop.

Grasping this is the key to repairing them. It goes without saying that the pin must not come into contact with the clamp on the contact in which the hardened steel tip fits as it definitely won’t work. It must be the hardened steel tip itself which now being clean and shiny allows the pin to brush past it smoothly and easily and make good electrical contact. Because the tip will often be shorter now than when new it is harder to set it up correctly and if there’s less than ½mm left you probably won’t be able to and will need a replacement spring contact assembly. Similarly a replacement balance wheel assembly will be needed if the pin has burnt through and partly broken off and the final part of this article describes how to remove and replace them. If the pin isn’t too worn away where it has previously been making contact you can leave the contact to touch at the same place as before so all that should be needed is to move it fractionally closer whilst constantly testing it by applying the current (see the next section to know when it is right). If the pin has worn away a lot you can reset the contact tip to touch the pin further along it on an unused part (the pin in photo 5 would be ok to reuse at the wear point if you didn’t feel confident about bending the spring contact to sit at a different point further along the pin). To do this hold the contact’s spring coil in place on its pivot pin with a tiny screwdriver and with another tiny screwdriver hook the contact at its 90º bend behind the metal tip and pull it towards the end of the pin. The “U” part of the phosphor bronze will bend (it won’t break.) This will tend to cause the tip to take on a slanted position in relation to the pin. Gently manoeuvre it to regain a 90º angle to the pin and with the new unused part of the pin brushing over the steel tip. Keep making tiny adjustments and live testing it until it starts to run properly once more. The next section describes how you will know!

HOW TO KNOW WHEN YOU’VE FIXED IT

Over the years, having replaced clocks thinking they were ticking away happily only for them to stop in a few hours, I’ve found there are two ways which will tell you whether you’ve done it and its going to keep working. Firstly when you’ve applied current give the balance wheel the slightest of touches. It should start immediately and even get up a little extra speed and rotation in a few seconds by which time the wheel should be rotating nearly a ¼ turn in each direction. When you sense it’s running at maximum speed cut the current and see how many times it continues to rotate back and forth before coming to rest. If it is 4 or 5 times you’re there! If this is happening there’s a secondary test you can try. With the current off move the balance wheel with your finger so the pin is below the spring contact and let it return slowly until the pin is resting against the underside of the contact – ie touching (the same position you had it in when you were cleaning the contact tip). Take your finger off the wheel, restore the current and it should start up on its own or, if not, with the very slightest of touches. (You can’t do this test with the pin above the contact as in this position they don’t touch when at rest). Put simply, you sense it really wants to go and is reluctant to stop when the current is cut – the exact opposite of what they normally do! If on the other hand it only rotates 1-3 times before coming to rest and the wheel isn’t rotating nearly a ¼ turn each way, although it may seem like its ok, do not be tempted to put it back as it will not keep working.

RECENTERING THE SPRING CONTACT

I referred earlier to a potential issue with the spring contact that is not readily apparent. This is that with use over time it may have taken on a permanent deflection from its correct position when at rest which should be with the metal tip pointing straight at the balance wheel spindle. If after cleaning and resetting the contact it is still not going well enough to fulfil the criteria in the previous section this may be the reason. To recentre it requires adjusting the coil spring on the contact to reset the position of the tip when at rest. I have found to my cost in the past that if this attempted by trying to pull at the coil or bend it in any way from above or below (it can’t be got at from either side of it) you will mangle it or the two coils of the spring will end up touching each other, either eventuality meaning the spring contact will be scrap and need replacing. In any case it is not possible to properly judge by eye whether it is properly centred without being able to look at it straight on. To adjust it accurately and without damage the balance wheel assembly must be removed. This is not difficult and is explained in the section below. With this out of the way you will have a clear view and access to the contact’s coil spring. Behind the contact tip you will see a coloured dot on the front plate which is the jewelled bearing for the balance wheel – photo 4 shows this clearly. This is your datum point. Viewed in a straight line the contact tip should be pointing directly at this (the picture wasn’t taken in a straight line). If it isn’t place your ½mm screwdriver (almost the only tool you use on this job!) into the outside loop of the coil spring and very gently pull it outward to move the contact downwards or slide the screwdriver inside the inner loop where it joins the centre and pull it round clockwise a little to move it upwards. When it is pointing straight at the jewelled bearing looking straight on at it, it is set correctly but you must ensure that the two coils are not touching each other at any point as this will inhibit the free movement of the contact and it will not work. With the screwdriver gently flick the contact (apologies for keep saying gently but it really is important!) up and down a few times to check that it always returns to its correct datum point.

REMOVING AND REPLACING THE BALANCE WHEEL AND SPRING CONTACT ASSEMBLIES

If you have on inspection decided that the pin and/or contact are unserviceable then you are going to have to replace them. You will, of course, need another clock, or better still clocks, to extract the parts you want and as previously mentioned, they are the same in all Smiths clocks of the period although a number of the other bits will differ. Of course if you have a Magnette clock (or one from a Wolseley 4/50, 6/80, 4/44 or 15/50 which I believe are the same even though they look quite different externally) which has the useable parts you need it may be better to clean and adjust and use that rather than replace the parts, in which case you won’t need to read any of the following unless you want the challenge! The clock in my current Magnette has a balance wheel assembly and spring contact from a brand new clock I was fortunate enough to obtain recently with the timekeeping screw and handsetting knob on the chrome bezel. I don’t know what car it was intended for.

REMOVING THE BALANCE WHEEL ASSEMBLY

To do this the T shaped bracket on the back must be removed You will notice there is a small obstacle to doing this, namely the cog on the outside of the bracket which sets the hands (seen in photo 1). This cog is a press fit on its spindle and though you won’t notice it unless you use a magnifying glass or have brilliant eyesight, there is a flat on the spindle and the hole in the cog to stop it turning on the spindle. The cog must be prised off to detach the bracket and it will be much tighter than the clock hands were. But I have always managed it. If you use the tried and tested two screwdrivers method definitely put something over it as it will fire off like a bullet, or if it’s stubborn, sometimes I have had to lever it up one point at a time working round. Don’t worry if the spindle bends a little doing this – it won’t snap and can be straightened again when the cog is refitted. Note that the way the cog has been pressed out in manufacture means the teeth are rounded off on the side that faces you and straight edged the other side. It should be replaced the same way round to properly engage with the handsetting knob. With the cog removed undo the two brass nuts securing the bracket and the two nuts securing the coil. There is no need to remove the coil but manoeuvre it downwards slightly to move the electromagnet arms away from the wheel. Then holding the movement face up carefully take off the T bracket together with the balance wheel manoeuvering the cam gear around the spring contact as you do so. As soon as the spindle has left the bearing in the front plate the wheel will want to flop about and just be sitting on the bracket but with the hairspring still attached to the bracket by a peg held in a hole by a grubscrew. Try not to let it fall off the bracket so it is hanging by its hairspring! Don’t panic if it does. The hairspring is surprisingly resilient and as long as it is not actually pulled or stretched it will not be damaged. You can if you wish detach the hairspring to allow you to completely remove the wheel from the bracket. I personally don’t usually do this partly because it saves a bit of time and also because the hairspring when attached to the bracket is what keeps the wheel and its pin and cam in their correct positions for refitting (ie don’t try refitting the balance wheel without the hairspring attached to the bracket or the cam will wrongly engage with the cup toothed gear and will jam and can be easily damaged.)

If you do decide to detach the hairspring, observe first the angle of the spring relative to the bracket where it is attached to the peg. The peg, being round, can be refitted in any position in the bracket so ensure it is replaced in the same position so the hairspring tension on the balance wheel is not upset and push it back so the outer coil is in line with the rest of the spring (see photo 5). Then tighten the grubscrew. Note that before detaching the hairspring from the bracket you will need to unhook the outer coil of the spring from the timekeeping lever at the top (see photo 2). On first observation this looks like it is trapped in a little box structure but gentle pressure with your screwdriver on the bottom edge which is contacting the spring coil will cause it to bend downwards and the coil can be slipped off. Don’t forget to refit the outer coil and bend the arm back up when replacing. As mentioned, I don’t do any of this but carefully place the bracket somewhere safe on the worktop with the balance wheel sitting on it.

You will now be able to recentre the contact if necessary and/or replace with another assembly. But do not replace it yet if you are also intending to replace the spring contact assembly as this requires the wheel assembly to first be removed.

REMOVING THE SPRING CONTACT ASSEMBLY

With the balance wheel assembly out of the way next remove the coil from its studs. You will already have removed the nuts. Manoeuvre the coil outwards away from the front plate until it clears the studs then turn it upwards from its left side so the wire which is wrapped around the stud on the right side can come round the other side of it allowing the coil to be moved out of the way enough to expose a large screw situated directly behind the coil’s right arm. This is the first time you will have seen this screw which holds the live feed terminal in place. (see photos 4 & 6). Unscrew this and remove the terminal and the round black spacer bush behind it. The terminal remains attached to the coil by the wire. Do not pull on this wire at all as it is soldered inside the coil to the finest of copper wire and as the sticky tape wrapped around the coil will have lost its stickiness and started to come undone the wire will break off very easily. It can though be reattached after unwinding the tape (which should in any event be reinforced with a bit of new sticky tape) by wrapping the copper wire around the feed wire a few times and applying a bit of solder. After removing the spacer bush this should expose a fabric insulating sleeve which is slid onto a long hollow brass bolt the head of which you can see on the front of the front plate. If the sleeve isn’t there then it has come off with the spacer bush and will be inside it. Pull it out. If the sleeve has stayed behind on the bolt slide it off and remove the bolt from the front. The complete spring contact assembly and earth pin can now be removed – note that the earth pin extends through the front plate. The coil will remain attached to the earth pin by its other wire (note it is not soldered to it but fixed by a natty little clamp.) If you want to reuse your coil just in case the one that comes with the replacement contact assembly is duff, just cut the wire off the earth pin and solder it to the new one (I don’t think any of us would have a tool to undo the little clamp!) The mica insulation plates fitted each side of the front plate will remain in place held by the screw holding the spring contact’s pivot pin and this shouldn’t be disturbed. The first time I sussed all this out I couldn’t help being surprised that the terminal to which the live feed attaches is secured to a bolt which is fixed to the front plate. If the fabric insulation sleeve isn’t fitted correctly there would be a direct and dramatic short circuit! (If the pivot or earth pins weren’t properly insulated at their fixing points there wouldn’t be a short circuit as the current would be passing through the coil but it would be a continuous current so the balance wheel would be held fixed in one position by the electromagnetic arms with the coil permanently live). If you are replacing the spring contact (or the balance wheel assembly) don’t forget to clean the pin and the metal tip of the contact before fitting them – much easier than doing it in situ!

REPLACING THE SPRING CONTACT ASSEMBLY

In the time honoured phrase, replacement is basically a reversal of removal but refitting the insulation sleeve correctly to ensure it passes through the front plate and buts right up against the bolt head can be fiddly (but very important!) I do it the following way. Fitting the sleeve on the bolt first before feeding it through the front plate and mica insulation doesn’t work very well as the fit is so perfect the sleeve tends to crease up and not want to go. So I slide the insulating sleeve part way through without the bolt, then slide the bolt into it so the sleeve fully buts up to the bolt head then push them both right home. Whatever you do after this the bolt must not be allowed to come out of the plate even slightly and then pushed back in as the sleeve may mov a fraction along the bolt and may no longer prevent it from making metallic contact with the plate. Slide the contact assembly along the sleeve up against the mica plate whilst engaging the end of the earth pin in its hole in the front plate and the spring coil on to its pivot pin. Still with your finger on the bolt head slide on the composite spacer bush and finally fit the terminal and tighten the screw securely. Manoeuvre the coil wires around the stud and move the coil down towards its correct position but don’t fit it on its studs yet until the balance wheel assembly has been replaced.

REPLACING THE BALANCE WHEEL ASSEMBLY

Before replacing the wheel assembly remember to check the position of the spring contact tip and recentre it if necessary as described above.

Refitting the wheel assembly is a reversal of the removal procedure but be careful not jam the cam up with the cupped tooth wheel as you fit it. Sometimes it can take a few moments to correctly locate the spindle ends back in their bearings. As you are doing this ensure the spindle for the handsetting cog is entering the hole at the bottom of the “T”. Don’t try to force the bracket fully back on the studs if the balance wheel feels tight – ensure it is properly home in its bearings. When you are satisfied all is well and the wheel is rotating freely, refit the nuts and tighten firmly (so if there is a next time they don’t undo with the outside securing screws!). Then press the hand setting cog the right way up back on its spindle aligning it with the tiny flat on the spindle and cog hole – you will sense when they are mated as you lightly rotate the cog on the top of the spindle. Pushing it right home (the spindle tip will be flush with the cog face) is important otherwise it won’t engage properly with the gear on the hand setting knob. Getting it fully home can be a bit tricky but pressure round the edges and the top of the cog with flat nosed pliers using the bracket edge as a grip will do it and if the spindle was bent at all when removing it pressure at the appropriate point of the cog with the pliers will straighten it up again.

You will now, of course, have to adjust the position of the contact in relation to the balance wheel pin in the manner described earlier and get it running to satisfy the tests outlined above.

REFITTING THE MOVEMENT BACK IN THE CASING

Firstly refit the grey alloy backplate to the clock with its smooth side facing outwards by clipping it onto the brass nuts. The coil is at the bottom of the movement and the plate is fitted with the screw thread for the handsetting knob facing down. An important point to note here is that if you have used a replacement spring contact assembly from a clock that had its handsetting knob on the front, for some reason these clocks were fitted with a shorter earth pin which means that the phosphor bronze spring strip on the backplate that makes contact to start the clock when you push up the knob won’t touch it. The professional way to rectify this would be to solder a bit of the old pin on the end of it but I have never bothered to do this. Instead I mangle and twist the end of the spring strip a bit so it touches the pin and (even more importantly) comes away from it when the knob is released. Not good practice I know but no one is ever going to see it. This can take a few minutes to get right but is do-able - just!

Refit to the case (it can only go in one way as determined by the timekeeping screw that emerges from the back of the casing). Refit the four securing nuts, the earth strap and the timekeeping lever. Clean the clockface and hands (clean the hands gently as the paint, being so old, will rub off easily) and refit them (the ‘6’ on the clockface pointing towards the screw hole!)

To get the hands perfectly aligned, I fit the hour hand (two small screwdrivers again) so it’s somewhere near the ‘6’ refit the handsetting knob and spring washer (and tighten) and turn the hand to point precisely to ‘6’. I then fit the minute hand pointing to ‘12’ which when right will be in a straight line with the hour hand. Refit just the glass with the four rubber corner buffers, then the front casing. I usually fit the green plastic around the clockcase first and then slide the front casing over it. Replace the grub screws if it has them. If not, hold the casing on as firmly as you can while at the same time pressing the ears down against the main case. To ensure a reliable earth for the illumination bulb I slip a thin wire inside the tube for the bulb holder which will be held in place when the bulb holder is pushed in and fit the other end to the screw that secures the earth strap to the case.

Well that’s it. I hope this article will encourage you to restore something that may not have been present in your car for very many years - the sound of ticking!