Clock Gauge Rebuild

[Carl Wilson]

Hello all. I'm back at work again. Six weeks aboard ship doing 12 hour shifts. I have 12 hours off each day and I like to spend an hour of this pottering - sometimes reading or working something out for a project I have in mind.

I've decided to take my old 10ths indicator away with me this time:-

I bought this from eBay some time back but just haven't really had time to devote to refurbishing it. Of course I have watched all of Doubleboost's friend Bob's videos on the subject, and I'll be studying them closely throughout.

You can see from the above and following pictures that it does require some TLC. I think it has been thrown at the bottom of an old toolbox for years. There is some minor corrosion on the body and the plunger. Also the lens is scuffed,which I think might polish out. The contact point is also corroded and the ball end is seized. I think most of the exterior rust will come good with very fine scotchbrite and light oil or possibly a fine glass fibre brush.

The clock seems to work well and both hands return fairly smartly. That said there is just the slightest suggestion of stickiness. I think that may be due to lack of lubrication and/or dust and dirt in the mechanism alloyed with the remnants of what lubricant there was.

Here are some more pictures.

In these pictures you can see the seized ball end and the missing keeper screw on the plunger. The bezel locking clamp and thumbscrew are present so no dirt has got in by that route. Hopefully.

As I say I'll be following Bob's knowledgeable videos with care as I proceed. Sorry about the bad shadow in the photos. I will try to get some better images when I start taking the unit apart.

 

[Carl Wilson]

I just noticed that one of those photos has an unintended "Arnolfini and his Wife" effect. Where the artist who produced that painting had painted himself, reflected in a small mirror behind the subjects.

 

[RonA]

If you intend to lubricate it you’ll need to seek out some clock oil don't use 3 in 1 or similar too thick.
RonA

 

[Carl Wilson]

I will have to see what I can find. Of course I'm mindful of Bob's advice when it comes to lubricants. A look at what the viscosity of instrument oil is will help. Straight off the top of my head I know I can put my hands on AWS10 hydraulic oil. This is pretty light, ie 10 centistokes. Still possibly too thick for this application.

There are many types of lubricants onboard and it will be a case of finding one that meets the criteria. The good thing about being here is I have access to good workshop facilities. Not quite like being in my own shop though!

 

[slim_boy_fat]

I just noticed that one of those photos has an unintended "Arnolfini and his Wife" effect. Where the artist who produced that painting had painted himself, reflected in a small mirror behind the subjects.

. You're safe, nobody would ever pick you out in an identity parade from that reflection.

 

[gordon stephenson]

Excellent work, Very sensitive, I preferred the analog to the later digital models.

 

[Carl Wilson]

I've got two digital metric indicators but I prefer analogue ones too.

 

[Carl Wilson]

Got started carefully dismantling the clock gauge today. First the contact point and bezel locking arrangement came off. Then after removing the backplate I popped off the lens with a very fine pick.

I next removed both hands using the approved method.

The next items to come off would be the return spring and crank arm. Both can be seen prior to removal below. At first glance there did not appear to be too much detritus inside the clock.

With the movement now exposed I became aware of a potential cause for concern. I noticed the the counterbalance spring sat neatly and uniformly coiled throughout about 3/4 of the spindle's range of movement. However in the last 1/4 of the travel, the coils of the spring slide up past each other and the whole bunches up to form a cone, telescoping upward. Perhaps this could be the source of the stickiness felt? I'm inviting comment on that.

Anyway, with the return spring and crank arm away I carefully removed the screws securing the journal plate. This also freed up the spindle guide block, into which, incidentally, the crank arm pivot bolt is also threaded.

The journal plate and spindle guide block were then removed. There was some oil and dirt build up on the journals and block, but nothing too drastic.

This is where I stopped for today.

I now think the next stage will be to remove the three black cheese head screws and the movement should come out of the front of the gauge. This will then leave the spindle in it's bearings in the main body of the clock.

I think the main issue is going to be trying to keep the counterbalance spring in place and preventing any unwinding. I also do not know how to clean the counterbalance spring shaft and the gear that is borne on it, since the spring is pinned to one of the journal plate stand offs, seen in the bottom right hand corner. Anyone has any ideas, feel free to chip in.

 

[RonA]

This what you need to remove the pointer safely. Mini instrument puller
RonA

 

[Carl Wilson]

Very nice tool and a fairly straightforward make by the looks of it. Thank you for sharing.

When I said it was the "approved method" for removing the hands, I was referring to the way Bob does it in Doubleboost's series of videos on clock gauge maintenance.

My current thoughts regarding the movement are that cleaning of the counterbalance spring shaft will just have to be done carefully in situ. I don't want to risk damage to a part for which there would almost certainly be no available spare.

 

[Shox Dr]

Do you have an ultrasonic cleaner? (Good excuse to buy one )

Place part in a plastic bag filled with acetone. Suspended over the tank, filled with water. Should give it a realy good clean without touching it.

 

[Carl Wilson]

Finished the strip down a few days ago.

The three internal screws secure the bezel, main dial and chapter ring by means of three tapped lugs. There is also a six pointed spring washer to preload the bezel assembly.

 

[Carl Wilson]

Some more pictures. The chapter ring is keyed to the bezel by means of a cut out and a minute pin. Similarly the main dial is located to the front face of the movement by two small dowels.

Looking at the guide arm on the spindle it seems to have some localised fretting.

All the gears except the counterbalance cluster. Also shown is the main hand drive pinion, together with it's support journal. This journal is secured by means of a countersunk screw and two locating dowels.

Once the bezel assembly was removed, three screws were revealed on the front face that held the movement in place. These screws seat in the peripheral curved slots. The radial slots are for the bezel securing lugs.

I now have to clean all the parts up and I can begin reassembly. There is an ultrasonic bath on the ship. If I can use it is another question. If I can't then I'll just have to clean everything carefully by hand.

 

[Carl Wilson]

The cleaning is going reasonably well so far. I couldn't get access to an ultrasonic bath. Therefore I've had to do all of the cleaning by hand.

This is careful, painstaking work with food grade contact cleaner, a small stiff fibre glass brush pen, air duster spray and electrical grade cotton cleaning buds. I've been holding many of the small parts with the aid of a set of Lindstrom tweezers, which have been very handy.

I have the main body of the clock with the spindle, the main dial and chapter ring and the lense still to clean.

The contact point of the clock has a seized ball end. I suspect there is a lot of microscopic pitting on the ball portion too. The rest of it has cleaned up well. I've thought about how I'm going to clean up and unseize the ball end. I think I'm going to try soaking it in a solution of citric acid. Even if the rust comes off and the ball frees up, I think it might be very rough to turn due to the pitting. I might have to find a contact point from a scrap clock to replace it.

 

[merryman]

Is the ball supposed to be loose? I can't see any point. Using a steel ball bearing makes sense as it is hard, the right shape, and cheap but I would have thought the metal would be peened round it, tight. Honda use ball bearings on the ends of tubular alloy pushrods in their engines, but they are firmly fixed to the tube, not free to rotate.

How did you get the bezel off the gauge? The pointer on my vernier calipers has dropped off and I can't find a way of removing the bezel to fix it back on again. Have replaced the verniers with digital, but the battery is always flat and it looses the display in cold weather, so I would like the old dial type working again.

 

[brightspark]

the ball bearing will be solid it is on all of mine. no point in it revolving it serves no purpose . it only contacts the material on the tip of the ball

 

[Carl Wilson]

Of course, it never occurred to me that the ball would be solid. No need for it to move in this application or a cam follower.

@merryman I will post more on how I got the bezel off. My gauge is Mercer. @doubleboost has his friend Bob on his channel who is the guru on this subject. He shows how to remove the bezel and strip a few different types of clock.

He inspired me to have a go at restoring this one.

 

[Carl Wilson]

@merryman

Here is how I removed the bezel. First of all I removed the lense with a fine pick. I used the pick just to carefully lever out the lense.

Next I removed the small and large hands. I did this using a method shown by Bob on @doubleboost youtube channel. Bob is John Mills's friend who services clock gauges. The photo below shows the method. Essentially one uses a pair of screwdrivers and two small pieces of wood or plastic to carefully pry the hands off their respective shafts, onto which they are a push fit.

@RonA has shown another method up thread using a small puller. I found the "Bob" method worked well.

I'd already removed the back plate from my gauge by this point. I turned the gauge over and removed the plate in which is held the journals for the various gear shafts. This exposed the interior of the gauge and it was possible to see three cheese head screws, shown in the picture below.


These three screws hold the bezel on by means of three small tabs. These tabs engage in a narrow groove machined around the inside periphery of the bezel ring. Removing these screws frees the bezel assembly. The tabs are shown in the picture below. Also shown are the six pointed spring washer that adds friction to the dial so it stays where it is put, the back of the main dial and the front of the chapter ring.

Here is a shot showing the peripheral groove in the bezel ring that the three tabs engage with.

Once the bezel assembly is off, the front of the gauge without the dials looks like this. You can see three more cheese head screws seated in peripheral slots. Removing these allows the main movement plate to be withdrawn from the body of the gauge. This has to be done very carefully indeed to avoid damaging the balance spring or losing the pinion shaft that engages with the spindle rack. Also shown here are the radial slots that the bezel retaining tabs sit in.

I've shown all these pictures before in the preceding posts, but I felt it was worth doing so again to try to clearly illustrate exactly how the bezel is removed. As can be seen, it is a fairly convoluted process on this Mercer gauge. I don't know if all Mercer models are the same as this. Certainly other makes are not.

As I've already said the best reference I've yet seen for this type of work is the video guides by John Mills's friend Bob, on the Doubleboost channel. Bob shows how to disassemble several makes of clock, including removing the bezel.