Rejuvenating a Chronometric Speedo

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Rejuvenating a Chronometric Speedo

Postby Group Leader » Sat Nov 03, 2018 12:04 am

Well, after 4000 odd miles my speedo has decided to be troublesome (or maybe it just wants a rest!).

The symptoms it developed were to occasional indicate speeds in excess of the speed I was actually travelling (I know the bike can't do anything near 80mph!) and then flick back to the correct speed. Last week it started doing this more and more until it was basically solidly stuck at 80.

Now I could, in slow time, send it away to the professionals but having read some of the interesting and more informative articles on the net I decided to follow the instructions and have a go at fixing it myself.

First job - get the bezel off. The gloved hand didn't budge it, even after letting some "encouraging solutions" soak into the threads for a good few days. So I got hold of a strap oil filter wrench and gave that a go but no joy. After some considerable faffing about and the application of a reasonable amount of gentle heat from a hot air blower the bezel finally yielded and so out came the innards. Unfortunately these seem to be fairly liberally coated with a thick oil/thin grease of a sort of treacle colour. Not certain where it's come from as the speedo cable is fairly clean and has, if anything a faint smearing of grey molygrease. The worm drive is dripping in it but also, up the other end the escapement rocker and cams are also covered so from what I've learnt it seems likely that it could do with a really good clean-up. To do so requires the chrono section being removed from the rest of it and therin lies the problem.

Try as I may, I cannot get the needle off of the output shaft. It is, allegedly, a push fit and can be eased off with a couple of screwdriver blades acting by rotating them gently against the dial face and the back of the central hub. Not in my case though ......

I applied as much twist as I dare but no hint of movement. Eventually I gave up and decided to do it properly and make a little puller (there's a small hole in the centre of the hub presummably for just this purpose). After a happy hour or so using my little Emco Unimat and a bit of filing etc said puller was made. As you can see it fits on snuggly but unfortunately there's still no joy shifting the pointer. Did a PO stick the thing on with an industrial grade epoxy - looks like it or am I just doing it wrong?

So I wonder if someone with real knowledge of the subject (e.g. Clive) could possible make any suggestions regarding what might be going on and why my puller doesn't seem to be cutting the mustard? Also, can they confirm that the gunk is likely to be the culprit causing my problem. Any suggestions gratefully received!

Speedo.jpg


Puller.jpg


In Action.jpg


Thanks,

Alan
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Re: Rejuvenating a Chronometric Speedo

Postby Dixter » Sat Nov 03, 2018 3:33 am

You might need to lengthen the small diameter end of the threaded shaft. The small end needs to enter the central hole in the needle hub, and be able to lift perhaps 3 mm.

Watch carefully for the small 3mm shims between gears on the various shafts. Use proper watch oil, and take care not to get any liquids on the mile meter painted surfaces. Very fragile.

Ciao, DC
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Re: Rejuvenating a Chronometric Speedo

Postby clanger9 » Sat Nov 03, 2018 9:23 am

As Dick says, the thin, fixed shaft is deep inside the hole you can see in the pointer. The pointer and the sleeve (that you can see) are one piece and should just pull off the shaft.
Once you puzzle out how a Chronometric works, it should be pretty clear which bit is at fault. The mechanism that "resets" the pointer every few turns is prone to sticking if there's any gunk on it. I washed mine off with meths, then applied a small amount of machine oil and it's been fine ever since.
Also, heed Dick's warning about the fragile number wheels. I made the mistake of trying to clean mine and the numbers just wiped straight off... :headbang:
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Re: Rejuvenating a Chronometric Speedo

Postby clive » Sat Nov 03, 2018 9:41 am

Hi Alan, the good news is you are probably correct about the problem being the grease. Basically what happens is someone (probably easiest to blame the PO) decides its a good idea to grease the speedo cable and runs it through their fingers covered in grease all the way home. This excess grease is then forced under Archimedes Screw action, as the cable rotates, up into the speedo. There is a slipping clutch which controls how long the drive is applied to "test" the speed. Once it starts slipping then the speed registered is too high and eventually goes round to the top speed and stays there. The camshaft assembly that is likely to be the problem is in the middle of the illustration on page 2 here http://archives.jampot.dk/technical/Speedo/Speedo_exploded_Views.pdf ignore the references to available etc as the company went out of business many years ago. I have always advised people not to grease the last 2 foot of the cable and rely on what has been already drawn into the cable outer by lightly greasing the earlier part of the cable. Don't use oil on the cable. Once you have cleaned up the innards be very sparing with any light oil used to lubricate the parts.
As to how to get the needle off, I have never had a problem using a single penknife blade rotated below the face and against the top plate below. However before doing this the 4 face screws have to be removed so the face can push up against the needle. I may be wrong but it does not look to me as though a screwdriver has ever been applied to those screws since it was built. Do it over a soft cloth as the face and needle tend to ping off together. If it all goes pear shaped I can probably supply a needle (Note to self severe telling off for advertising on the forum!). As Dick says watch out for the numerals and face, the earlier ones were painted by blown powder paint and come off the second you touch or try to clean them. In the illustration yours looks to be the later type which are more robust.
good luck, there are more parts in the speedo than in a single engine!
clive
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Re: Rejuvenating a Chronometric Speedo

Postby Group Leader » Sat Nov 03, 2018 10:19 am

Many thanks for all the advice chaps, very helpful.

I will make the point longer to go further down the hole as Dixter mentions. Can't think why I didn't spot that - in my defence I'll put forward the excuse that it was late last night when I got the puller done and I was tired ...... Anyway, I'll give it a go.

Clive may well be correct in the assertion regarding the screws. I certainly haven't touched them yet as I thought I'd leave the dial intact whilst I faffed with the needle but actually that seems like a good plan as the the screw drivers/blades can then push on the back of the dial so any marks won't be seen. I did try putting something behind the dial to support it and give the screwdrivers more to react against but to no avail.

With regard to the gunge. I'd seen mention of the need to keep at least the top end of the speedo cable dry and I've not disturbed it previously. It may well be that a previous owner of a another bike over-lubricated it as the speedo is not the original, as was pointed out to me in my earlier thread on how to reset the trip meter - the speedo is actually a later headlamp mounted one. What puzzled me though was how the gunge got up the escapement end if it was an over-oiled cable. I think an over-lubricated instrument is probably to blame and maybe now its colder it's just too thick.

Comments on the fragility of the markings also noted.

Anyway, I'll report back later and thanks once again.

Cheers

Alan
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Re: Rejuvenating a Chronometric Speedo

Postby 39speedtwin » Sat Nov 03, 2018 1:28 pm

Alan, as you know Clive is the pro!
I have had several instances of grease in the movement, after removing the needle and face, I use an aerosol can of brake/carburettor cleaner, but be careful not to get it on the milometer drums.
Just take care.
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Re: Rejuvenating a Chronometric Speedo

Postby Dixter » Sat Nov 03, 2018 1:37 pm

Hi Alan, your timing is excellent. A week ago I serviced an old speedo for my ‘46 G80. The symptoms were much like yours. I’m attaching three articles I found on the web. The first from the Vincent Owners Club was excellent at showing how the needle shaft worked.

http://www.voc.uk.com/net/docs/10.1/10.1-653-27.pdf

This shows the construction of needle shaft and individual components. Being of a concentric nature, I could readily see that old sluggish lubrication inside a sleeve limited free movement of the needle. Armed with the camera in my phone, a clean sheet of paper toweling on which to arrange parts, and an assortment of small screw drivers, I completely dismantled the ‘clock’ portion of the speedo. I left the mileage meters intact and attached to the frame, remembering a sad experience from the past.

Washing the shafts, bearing plates, and various cogs was done with an artists brush and some mineral spirits, and blotted dry. I had some clock oil on hand. I spent a few pleasant hours and put all right. Neatness and grouping component parts with their mating fasteners paid big rewards, as did having many images on the phone close at hand.

Here are the other two articles.

NB having a nice pair of tweezers is a big plus. One tiny ‘click’ sound and seeing the glint of a flying screw will change your entire day.

Ciao,
DC

http://www.hells-confetti.com/Technical ... hanism.pdf

http://www.wdbsa.nl/Jaeger-Chronometric-Overhaul.pdf
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Re: Rejuvenating a Chronometric Speedo

Postby Group Leader » Sat Nov 03, 2018 3:34 pm

Armed with a longer "Pointy Bit" I had another go with the puller and initially the pointer still refused to budge. Armed with the knoweldge that if the pointer did succumb there was a potential source of replacement I became bolder (i.e. I screwed the rod down much harder despite the pointer arms bending up slightly) and eventually it came off.

I removed the screws and then the dial and found the paper backing sheet stuck to the four mounting pillars with a some sort of blue adhesive and so the paper backing had to be surgically removed with a scalpel but we got there in the end :)

Dial Off.jpg


I removed the clock mechanism and, discretion being the better part of valour, decided to just imerse the mechanism in some meths and give it a good clean with small Sable paint brush. I'll save complete dismantling until a) I have a spare or b) I have to. Particularly stubborn lumps of gungy grease were helped along with the tip of the scalpel. Not possessing any clock oil I settled for some very thin silicone trumpet valve oil (I used to play the trumpet at school ~50 years ago and I hate to throw things away :D ) which seemed to do the trick nicely. I also cleaned as much of the gunk from the drive worm and gear using some dry cloth - I thought sploshing meths around however delicately might be asking for trouble.


Here are some before photos (sorry they are not of the finest quality but they sort of show the imortant bits)

Before 1.jpg


Before 2.jpg
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Re: Rejuvenating a Chronometric Speedo

Postby Group Leader » Sat Nov 03, 2018 3:48 pm

And here are a couple of after shots.

After 1.jpg


After 2.jpg


After re-assembling it all a quick test on a battery powered drill showed that it was working up to ~ 20mph so I reset the trip and odometer (it's not the original speedo and how many miles the bike is lost in the mists of time and, oh yes, I'm not going to be selling it anytime soon :D ) I was going to set it to the number of miles I've actually covered but as has been mentioned elsewhere it's easy to set them to zero but harder to go from zero. I'll just have to add 4411 to the odometer reading to keep a tally.

There was nothing for it but to test it properly so I was forced to go out for a spin. It appears to be working perfectly up to 58 miles an hour although I'll check the calibration when I next pass a radar speed indicator.

I have to say I think the Chronometric speedo is a wonderous device. What a superb bit of engineering/clock making. It is astonishing that these old instruments still perform their function after all those years and miles in a relatively harsh environment. I'll be looking out for a correct one for my bike and look forward to doing a more in depth restoration -I'll get my tweezers ready!

Thanks chaps for all of the advice and guidance. I know a lot of the comments have been made previously on old threads (I did spend an hour trawlling through them the other day) but it really helps to have a bit of interactive dialogue as you go.

Cheers

Alan
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Re: Rejuvenating a Chronometric Speedo

Postby Pharisee » Sat Nov 03, 2018 5:27 pm

The springs on the pawls that drive the odometer ratchet reels can weaken with age. I had problems with the main odometer and trip odometer on my G3 speedometer 'missing' miles and getting out of step with each other. After a lot of taking apart and putting back together again with no really positive result, it was put down to vibration causing the pawls to miss teeth (they always under read, never over read). It was only cured when another, slightly stronger spring was used to keep the pawls in contact with the ratchet wheels. There may be a penalty to pay in slightly increased wear on the pawl tips but I'll cross that bridge if and when it arises.

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