Smiths "Bijou" movement stopping - mystery solved?

[Nickthedentist]

Hello electric clock experts,

The little Smiths "Bijou" movement was used in most of their electric timepiece from just before the War until the late 1950s. After a quick stripdown, clean and re-lubrication, they usually work first time and give the impression that they will run silently and accurately indefinitely. Wear is almost never seen, which is not something you can say about all electric clocks.

But I've had a few over the years which are hard to start and then stall after a few seconds or minutes. Very frustrating! I've always put it down to a weak (de-magnetised) rotor, because that's what the service info suggests, even though the rotors always seem to have plenty of torque when operated on the bench, separated from the rest of the movement.

But I now think that it's due to the rotor bearing spring, a flat piece of springy metal that exerts light axial pressure on the rotor pinion bearing, keeping the rotor sat properly on its bearing in the stator.

As Smiths experts will know, there were countless "improvements" to the movement throughout its lifetime, and the rotor bearing spring (as well as the rotor bearing cock that supports it) are no exception.

All the faulty clocks had a RBS made from a copper-coloured material with a small hole in it, which allowed rotor's arbor to poke through the spring, allowing the spring to foul the rotor pinion, causing excess friction.

So what's going on, then? Is there meant to be a hole, or has it just appeared by the "drilling" action of the rotor over the course of 60+ years? Or was the hole meant to be small and has become enlarged through wear?

Note that my oldest (1938) Bijou has a different cock and spring arrangement which is immune from this problem.

Sorry for the poor pics [to follow in a minute] - I've used cropped pics from my files as opposed to taking new ones.

Nick.

[Nickthedentist]

Here's a picture of the old-style cock and spring. There is no hole, the springy bit is made from spring steel(?), and it gives no trouble:

[Nickthedentist]

Here are some pics of the troublesome, post-War cock and spring, which has a small hole in it.

In this later design, the spring sits under the rigid cock, and so is hidden in the LH image.

[Nickthedentist]

And look at this! The hole in this example is way off-centre. Surely it wasn't made like that, but the hole has appeared through wear, off-centre because the spring wasn't carefully aligned when it was fitted to the movement. So maybe these had no holes in them originally.

All comments welcome.

Thanks, everyone.

[keithinuk]

Is there any way to date the movements, as I have one that has an all brass movement?
It has a habit of running backward when started.

[Nickthedentist]

Hi Keith,

The date is often stamped on the front of the front plate, along with the model code "BJM".

The earliest one I have is 1938.

The one pictured in post 1 is from 1947, and is all-brass, like most of the earlier ones.

Nick.

[keithinuk]

I found it on the front of the front plate, not on the brass plate as your picture.
BJM 167, 3 47.

[Nickthedentist]

My picture is of the front of the front plate, Keith!

I have always presumed these stamps to include the date, but it seems an incredible coincidence that yours says "3 47" too, so maybe this is not the date after all.

Thanks for your interest. It seems that fewer members are interested in electric clocks than I thought, especially now Darren Kitson's no longer posting. Nick.

[TomStroud]

Hello!

I am new to this forum, but discovered you yesterday when dismantling an old clock (1930s art deco wall clock) which my grandparents have had since it was new. It seems to have worked for the last 70 years (which is pretty impressive!), but stopped working earlier in the year. Being an engineer, I have taken it upon myself to get this working again.

It has a Bijou motor, which I have dismantled, and the parts seem to be in good condition, with little wear.

Having dismantled the clock, I have come to the same conclusion as you - the little copper spring under that brass clip seems to stop the first cog turning - I have put the clock back together, and if I hold the spring back with a screw driver it seems to work OK. I can only imagine that the hole in this spring was made by wear.

Has anyone else seen this problem? Would anyone be able to suggest a suitable material supplier for buying a tiny strip of copper so I can make a new one?

Thanks for your help!
Tom Stroud

[Nickthedentist]

Hello Tom,

I'm glad that you've found my posts (and this excellent forum), and have something to say on the matter - you're the first to do so in 3 months of the thread being started.

70 years with probably nothing more than a quick service (at best) is indeed impressive.

I'm still not certain whether the cock spring is meant to have a small hole (to keep the rotor's arbor centred), or no hole at all. I suspect the latter.

I've not had the time to experiment to find a cure yet, but certainly making a replacement would be ideal. You could try a modelling shop.

I had toyed with the idea of fixing a small "patch" of spring steel (cut from an old clock spring or similar) over the hole with nothing more than Superglue, leaving the rest of the cock spring original.

Whatever the rotor's arbor revolves against would have to be hard enough to survive without wearing through too quickly, and hard usually means difficult to shape, hence my desire to repair the cock spring rather than replace it entirely.

Are you out there, Mr Phelan (our resident clock expert)?

Nick.

[paulsherwin]

Isn't it possible to adjust the spring so that the bearing doesn't run in the wear hole?

[TomStroud]

Thanks for your quick comments.

I will look into spring steel - sounds like a good idea.

Paul - It would be hard to adjust the position of the spring as there are two holes in the other end which locate it against a screw and a support pin - I dont think it is possible to move its position easily

I'll try and post again later in the week when I've had a chance to look at it again!

Tom

[Mike Phelan]

You called, Nick?

I'd say there shouldn't be a hole. You could make a spring from a piece of cheap feeler gauge to get the thickness right; should be tempered enough to make a hole.

[PaulR]

There is a similar spring in a Ferranti chiming clock I have. The rotor arbor actually runs on the top of a "pimple" pressed into it. Recently the clock was running very noisily and I thought that the spring had lost some tension so I decided to make the "pimple" a bit deeper using a punch. The result was a hole instead of a pimple! I found a small brass screw to fit the hole which acts as an adjustable bearing. Would something like that help here?

Paul

[Mike Phelan]

No, Paul, the spring needs to be replaced. The idea was to have point contact and less friction with the pivot being domed and the flat spring.

I've a Ferranti chiming clock (actually branded Smiths before they designed their own) but the spring on that is flat as well.

You want as little friction as possible as there's very little torque available; the spring only needs to prevent any endshake on the rotor.

Clock bodgers were rife over the centuries, which is probably where the dimples and pimples came from.

[TomStroud]

I've fixed it!! (mostly). I couldn't find any spring steel for sale in sensible (ie tiny) quantities, so have just superglued a piece of aluminium can over the hole on the existing spring. Its now working again - although I will need to take it apart again to replace the aluminium with something more permanent in due course.

The only issue left to sort out is that it doesn't 'self start' - and wont start when you twist the rod sticking out of the bottom either... the only way to start it is to take the cover off and give the cogs a push with your fingers... this is clearly not ideal as there is 240V not far away! Thanks for your help! Tom

[Mike Phelan]

That's probably because of excessive friction in the rotor "mod" or it all needs a clean and lubricate.

[Nickthedentist]

If it's a non self-start version, the rotor should be shoved into rotation as the hand set knob springs back into position. If there's gummy grease on it, it won't spring back sharply enough to have any effect.

And thanks very much for your comments (post 13), Mike.

Nick.