Jaguar clock repair

With lots of parts out at The Surgery for the test fit, I’ve had time to indulge in some “minor but interesting” projects – this won’t be the case shortly when everything arrives back in my garage!

Contents

Overview

While playing about with Jag tachs, I acquired a spare clock in one of the Daimler tachs I purchased to experiment with. This got me wondering about a DIY approach to getting the ever problematic Jaguar Clock working, most of which failed within a few years of leaving the factory. The reason for this is well documented on forums such as Jag-lovers; the clock is an electromechanical design that relies on tiny contacts to create a series of magnetic pulses via a coil which drives the clock mechanism. After a few years the contacts wear out, and the clocks enter the “right twice a day” setting familiar to most Jaguar owners.

I’m aware of various suppliers who provide a repair service for these clocks, but that means sending my clock away for repair, and I like DIY where possible. After some internet research I discovered Clocks4Classics who offer a DIY repair kit for these clocks.

The Clocks4Classics solution bypasses the problematic original design by replacing the mechanical points with an infrared sensor; a microprocessor controls the current in the solenoid coil, creating the magnetic pulses required to drive the mechanism. A full description of the failure mechanism and the Clocks4Classics solution is available on their website. A quick browse of the website convinced me to purchase a kit to try.

I decided to test the kit on the clock from the Daimler tach mentioned above. For whatever reason, this clock and the one in my car have the same screws missing from the case. Strange.

Clocks4Classics provide comprehensive instructions and video guides of the process of installing the kit, which is just as well as most of us are not skilled at clock repair. My LED magnifying lamp, purchased from Jaycar electronics, was invaluable when dealing with the many small parts in the clock.

Disassembly

The first quirk I discovered was that someone had added what I guess was a grounding wire to this clock at some point. Probably this was an attempt to get the clock working. In fact, the small fusible link seen in the image below provides the ground connection.

Undoing the machine screws on the rear of the clock allows the case to be removed, exposing the internal mechanism. You can see the contact pin on the balance wheel just touching the wiper contact in the image below. Click on the image for a full-size view. You can also see where the pin has been eaten away by the small arc that occurs when the current is interrupted when the contact wipes over the pin. This arcing causes the clock to fail.

I connected the clock to my bench power supply and gave the balance wheel a good flick. To my surprise, the mechanism wasn’t dead. It staggered along for a few seconds but could not provide enough energy to maintain the balance wheel’s oscillation. I couldn’t resist giving the pin a good scrape with a knife blade which produced a noticeable improvement. It managed 20 seconds or so before giving up the ghost. Better, but not of any practical use.

Anyway, after that excitement, I began the disassembly process as per the detailed instructions on the Clocks4Classics website. What follows is my highly summarised version.

The first step is to remove the clock face; the screws are tiny and tricky to remove. I then cut the solenoid wires as close to the ends as possible and removed the solenoid.

Next the connector bracket and the balance wheel assembly are removed. I was nervous handling the balance wheel for the first time as I didn’t want to damage it, but you soon get the hang of things.

The instructions refer to a plastic connector bracket support; my clock didn’t have that. I believe these were fitted to later versions and incorporated a diode intended to reduce arcing at the points.

The next steps involve removing the small gears – the escape wheel assembly and transverse wheel assembly – and the contact pillar assembly – which is no longer required. Thankfully, the instructions have all these parts clearly identified which helps keep track of things.

Cleaning, fitting the board and reassembly

The instructions state that the parts should be cleaned in isopropyl alcohol or clock cleaning fluid. I put the components into a small dish with isopropyl and swirled things around for a few minutes which seemed to do the trick. I then laid everything out on a cloth to dry.

I found the video instructions invaluable for oiling the bearings (I chose the kit option that included clock oil) and refitting the transverse gears and associated parts. This is fiddly work; patience and tweezers are required.

The PCB comes with a note in the kit mentioning that it can be sensitive to static discharge, so I assembled these parts on an anti-static mat. The connector bracket retaining screw holds the PCB in place.

The kit includes a sticker (with a black marker stripe) which you stick onto the balance wheel. The sensor uses this stripe to determine the position of the balance wheel. You can see this sticker in the video below. Next, the balance wheel, its support plate, and the solenoid are carefully refitted. Again all this covered in the detailed instructions.

Test

After pushing the solenoid wires into the connectors on the circuit board, the clock can be tested. I hooked the clock up to my bench power supply, took a deep breath, turned it on and … Yes!! One working clock.

In my hurry to test the clock, I didn’t position the brown insulating plate shown in the video correctly. See the images in the disassembly section above for the proper orientation. I also cleaned off the tiny spec of corrosion around the centre spindle in the base plate, although this looks much worse than it is due to the close-up view in this video.

Final Assembly

The final step is to refit the dial face with the hands in the 12 O’Clock position; this is tricky as the minute hand has quite a lot of backlash. Now the clock mechanism can be fitted back into its case and mounted in the tach.

I ran a test to determine the timekeeping accuracy by connecting the clock to a small 12V battery with an in-line fuse. At this point, I noticed the hour hand looked 1/2 an hour out, so something had gone wrong when I set the hands.

As I had to take the dial off again to have another go, I contacted Clocks4Classics about this and received the following reply from Mark Willows.

“With regard to the hands, there is often quite a lot of backlash in the dial mechanism – sometimes the minute hand will move quite a bit before there is any movement on the hour hand, and this can upset the alignment of the two hands.
You can compensate for this in the following way: when you have set the hands to align at 12:00, use the time setting knob to turn the hands anticlockwise to around 11:45 and then turn them clockwise back to 12:00. If the hands no longer line up, then re-adjust their position slightly and repeat the procedure until they align correctly when turning them clockwise towards 12:00.”

I tried this, and after a few attempts, everything seemed to line up correctly, so time for another timekeeping test.

Timekeeping: The clock is surprisingly accurate (IMO) losing around a minute over seven hours in the initial test. After some adjustment and following a tip in the instructions to set the hands a couple of minutes fast to accommodate the backlash in the mechanism, I managed to get things to the point where the clock was accurate over a 30 hour time period.

This is a fun project — Initially, I was a little nervous handling the small parts, but I took my time, and there’s a great sense of satisfaction seeing these little clocks burst back into life again. And to hear them ticking happily away!

Oh, and remember those missing screws; I managed to get a parts clock from the Jaguar Spare Parts club (see blogroll for link). The quid pro quo being that I fit the Clocks4Classics kit into two additional clocks for club stock. Which I’m happy to do.