Bringing a Smiths car clock to life

This has been on my to do list for years and I may just have sufficient knowledge to do it now. These 1960s Smiths clocks sit in the lower of a Smiths Rev counter and are a separate unit. It's a clever mechanism so might be of interest to some here. Nowadays, I suppose all car clocks are quartz but before the advent of stepper motors, Smiths needed a way to make a cheap movement to do the same thing.

Here in my '63 E-Type. I'd previously stripped all the gauges and cleaned them but kept putting this clock back in without even cleaning it's case. Always next month, well next month arrived. This did work intermittently years ago and makes a noise similar to a mechanical watch.


Out of the car with the setting cable (found after thirty minutes in the garage..). The dial part is only about an inch in diameter and the case closer to two inches.


The back with one electrical connection (the earth is through the rev counter body) on the right. My car was positive earth when made so it says "feed lead negative". Makes no difference as it works with negative earth. There's a hole to turn the regulator just above the central shaft but, it's hidden. The mechanism is held and suspended from the body on the four big screws sitting in rubber bushes but, one of them is earthed with the little strip. This means the whole movement is earthed so the electrical parts sit on insulators.


Out of it's case and on the dirty strip down mat. There's a balance wheel and hairspring with regulator on this side. It's this side that needs to be connected to earth as the electrical path is through the hairspring....


On the other side, a coil to generate a magnetic field.


Better view of the balance and hairspring, stud on the right and regulator in the middle, with the screw that comes through the case to adjust the rate. The balance has three permanent magnet segments. This cap jewel is one of the three jewels (the other two being for the balance pinions).


Balance removed. The balance drives the movement and is not there to control the energy release from a mainspring. When it swings, it drives the brass collar on the right hand shaft (that shaft has a piece of spring steel resting on it to stop flutter). When that shaft turns, the worm gear drives the horizontal shaft and it's worm gear drives the central shaft via it's wheel.


On the 'dial' side, the central shaft drives these gears to run the minute and hour hands on the long shafts. Note that some halfwit used red loctite to attach this side meaning I had to heat it to get the screws out...


Here's the balance turned over. The black ring is the one that drives the brass collar above. There's a pin sticking down close to the shaft and as it swings, that contacts the spring in the next picture to complete the circuit to earth via the balance spring. There's some burning on the balance probably caused by arcing due to poor earthing. It also has Endshake measured in mm so, it may be touching something.


Here's the electrical parts removed. The one connection on the back goes to the coil on one side and the other side of the coil is connected to the post with solder. That's connected to the post at 12 O'clock via a spring and the prong sticking out is the one that contacts the pin on the balance wheel.


This is pretty clever and like a small DC motor (although usually, the armature has the magnets controlled by the power). But, it can't be allowed to turn continuously so it needs to be stopped and started.

When the balance swings the pin contacts the prong above completing the coil circuit and generates a magnetic field down the two curved arms. The permanent magnets in the balance react with that to give an impulse to the balance and the mechanism is driven. It's all controlled for rate by the effective balance spring length the same as in a mechanical watch. To start it, the circuit is completed with another mechanism.

It has some problems, excluding the dial and hands that I will need to repaint. The pin and prong are working like points in a distributor so get eaten away. I suspect this is the biggest problem with it.

Easy to repaint the dial but, I want to keep the writing, which is just the Smiths part number. Made the mistake of trying to polish out a score and now it's terrible...


Hands will be fine when painted.


So, it's stripped and will be cleaned (I'll take any oiling advice) to see if I can get it going again.

Cheers, Chris

Hi Chris, that's an interesting project you're working on. Regarding the problem with the dial, why not paint it black and re-do the writing with white Letraset.

You are suggesting a redial?

Don't think it will influence the value of the car but I would still not like the idea..

I sure am, I bet the rest of the car is not original.

Why bother painting the hands and keep a scabby dual? It's not a Patek.

Thanks for the ideas. The numbers and ticks are on the rev counter dial so, it is basically a satin black dial here with just the part number. It seems that most restorers just spray the whole thing black and lose the numbers but I was thinking to mask the number block and spray the rest. It's only black after all so it might blend.

The worst thing is that it was hardly noticeable before I decided to "improve" it. It's only a 25 mm diameter dial and is about half a metre away and this is the problem with looking at it through an eyeglass. Ah well, committed now.

I mounted the balance again to clean it using new solution as I didn't want the magnets picking up old particles. They're very weak anyway. After that, removed it and cleaned the plate again to be sure the jewels are cleaned.


The biggest concern is the pin that is used to complete the contact as it is very worn.

I think this is why the Endshake is so large as at the previous service, the guy may have been trying to get it to work on a different area of the pin. This and the prong must have had a treatment from new but, it's long gone.

Let's see if I can get it running...

Cheers, Chris

Thanks for that. Very interesting. Great pictures.

great project. i have some experience with car clocks ( and pannel clocks {aircraft}). my best advice is to send the dial out for restoration (hope it is not radium) AND replace it in the pannel as - not running - and not wired up. it would increase the value of a jag. remember " lucas is the saint that invented the dark" - vinn2

I thought that Joseph Lucas was the Prince of Darkness. Didn't realised he'd been canonised.

the only thing i know about lucas; is wireing and brakes. the jag is a fine collector car, but like any auto, they all have problem areas

Definitely "Prince of Darkness", plenty of tales about turning on lights to get only a puff of smoke. I've been lucky and my switches have been well sealed so the smoke is still in there and hence they still work.😉 Anyway, all gauges are Smiths.

You're right, Al, the balance staff is orientated fore/aft so the end shake would vary under acceleration/braking. The rest of the time it sits on one side of the jewels. They are pretty good. The end shake was so large that the staff was barely retained. Compare this picture to the balance above and you can see 90% of the pinion.

The screw I'm pointing to here is directly behind the plate jewel and adjusts end shake by moving that jewel.

This is quite neat but, I didn't pay lots of Euros to Horia to then use screwdrivers 🙄 so I pushed it through to bring the end shake to 0.1mm, still loose but these are big pinions.

I may go with HP1300 for the lubrication as I don't have anything with higher viscosity. You're right, it is probably a slow 1Hz movement but it's been years since I heard it. All bearings pegged 👍 and look pretty good. These clocks don't get a lot of use as they are usually broken.... I'm not used to seeing worm gears used like this and am wondering if they might benefit from a light lubrication?

Good news is that the coil checks out so, the electrical side seems fine and will just get a clean with contact cleaner.

Cheers, Chris

Hi Vinn2, I'll sort the dial out but, it is just the plain black circle you see above with CE 1111/01 written in it without any hour markers. Most people just spray the dial satin black and obscure the writing, which is just the Smiths part number, but I'll see if I can retain it. Not really worth sending it out to be honest. I would like it to work though but it adds nothing to the value of the car.


They are becoming collector's cars which is a shame as people are buying them as investments but they should be used. This is pushing the prices to ridiculous levels and out of the reach of enthusiasts. I'll take mine to work tomorrow which starts the day nicely 👍. You can use them everyday and I have in the past.

Yes, there can be problems mainly because they need setting up properly. There are lots of adjustments and shims to set up the front and rear suspension, for example. People just get this wrong and they are complex cars - someone once said something like "there is more going on in one door of an E-Type than in a whole MGB". He's not far wrong.

The biggest problem is the rear suspension set up that ruins most of them leading to poor handling and ride. For example, people rotate radius arm bushes through 90 degrees because they "Know better than Jaguar" and this screws up the way the suspension works.

The inboard rear disc brakes get neglected as well and they get very hot on the track. If you don't replace the fluid regularly (which is not a quick job), you'll possibly boil the fluid in that circuit under hard use such as braking hard at the end of the Lavant Straight at Goodwood. Ask me how I know....

Set up and maintained well, these are terrific cars though 😀

Cheers, Chris

A little off topic, but since we're talking British engineering: I once shimmed the Isolastic suspension on a Norton 750 such that there was no perceived vibration at any RPM. It took me two days.

i stand corrected. that driving your jag every day will counteract the lucas effect. --vinn

Nice project.

Interesting that the balance staff pivots show so little wear, most probably the clock hasn't run very much in it's lifetime.

There certainly a lot of wear on the electrical contact pin, probably best to replace it if possible. More than likely the wear is due to sparking on disconnect with the collapsing magnetic field, in the aviation industry we used many relays and always had a reverse biased diode across the coil to ground out the collapsing field and avoid pitting of the contacts, if the principle of this set up is similar electrically, you may want to consider adding a diode and extending the life of that contact pin.

Certainly the pin wear vs the pivot wear is very uneven, looks as if the weak point is going to be that pin.

I would probably leave the worm and wheels dry, just make sure that they are very clean and they should be fine, oiling them may increase the sticktion to the point that it could affect the running.

Thanks Rob. I think you're right, these clocks have wear almost entirely on the electrical contacts which stops them so pivot wear is minimal. As you say, probably best to view that worm gear as a conventional wheel so no lubrication.

That electrical side is a weak point and I was thinking a capacitor there in the same way as contact breakers in a distributor but a diode would probably be better. I will have a think but certainly have some suitable diodes in my tool box. I doubt I can do more than just polish the pin as it must have had something like a hard chrome plate originally so anything I put is likely to wear quickly. I'll see if I have something suitable though.

Will post when I have some re-assembled.

Cheers, Chris

very good idea - that diode. i have repaired 12 volt car clocks by just cleaning the contact points. your diode idea would have eliminated the "the contact point problem. thanks -- good to have an electronics man in the house