Rejuvenating a Chronometric Speedo

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Re: Rejuvenating a Chronometric Speedo

Postby clanger9 » Sat Nov 03, 2018 5:50 pm

Top job! Chronometrics are marvellous things, aren't they?
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: Rejuvenating a Chronometric Speedo

Postby aobp11 » Sat Nov 03, 2018 7:06 pm

clive wrote: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.
Those who are familiar with the working principle of the speedo know of course what Clive wants to say. For others it may sound a little strange or contradictory.
The clutch is always slipping. The problems start when the friction force in the slipping clutch drops too far.

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Re: Rejuvenating a Chronometric Speedo

Postby 56G80S » Sun Nov 04, 2018 8:33 pm

Great thread and photos.

I've bookmarked tis. I had my Chrono rebuilt by Autotempo quite a long time ago and over the last couple of years the register of speed has become more "stepped" although still relatively accurate (over reads true speed by about 4/6 mph at indicated 70 mph).

And the trip has stopped resetting.

So if I get other things sorted I might attempt a clean up. No response required to this just thanks for the account of progress, pictures, references and guidance.

Johnny B

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Re: Rejuvenating a Chronometric Speedo

Postby Group Leader » Mon Nov 05, 2018 10:19 pm

56G80S wrote:......... just thanks for the account of progress, pictures, references and guidance.


That is the joy and benefit of a good internet forum - to have literally hundreds of years valuable experience on tap to help the new boys like myself out is invaluable. Hopefully, by posting the trials and tribulations encountered will help others too, infact, you've just confirmed it :)

I've found on many forums, relating to a host of different interests, that you very quickly spot the bods who really know their onions (and the ones that don't) and hence the ones to trust and it's certainly no different here.

Just to wrap up then; the best video I could find of this splendid device in action - how fiendishly clever!

https://www.youtube.com/watch?v=_csMpNiqLw4

Alan
1953 AJS 16MS and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:

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Re: Rejuvenating a Chronometric Speedo

Postby Flash » Tue Nov 06, 2018 10:11 am

I don't believe I could tackle the hassle of trying to repair a speedo these days, trying to hold anything small I do tend to shake quite a bit, even small jobs like soldering if I have to hold two elements together, I'm lucky if I get it spot on. I have just recently sent off a chronometric speedo to Chronometric Instrument Services in Nottingham, who do a complete refurbish, re-calibrate to your requirements for £140 plus £8-50 postage, looking forward to its return now.

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Re: Rejuvenating a Chronometric Speedo

Postby Richard Mills » Tue Nov 06, 2018 5:25 pm

Flash wrote:I don't believe I could tackle the hassle of trying to repair a speedo these days, trying to hold anything small I do tend to shake quite a bit, even small jobs like soldering if I have to hold two elements together, I'm lucky if I get it spot on. I have just recently sent off a chronometric speedo to Chronometric Instrument Services in Nottingham, who do a complete refurbish, re-calibrate to your requirements for £140 plus £8-50 postage, looking forward to its return now.


I would be pleased to hear what you think of their work once you have it returned and installed.

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Re: Rejuvenating a Chronometric Speedo

Postby JDFS79 » Tue Nov 06, 2018 10:48 pm

I have used the same chronometric service, and they are very good , a little expensive for me, but if you want perfection they will do it.

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Re: Rejuvenating a Chronometric Speedo

Postby Pharisee » Wed Nov 07, 2018 9:40 am

Richard Mills wrote:
Flash wrote:I don't believe I could tackle the hassle of trying to repair a speedo these days, trying to hold anything small I do tend to shake quite a bit, even small jobs like soldering if I have to hold two elements together, I'm lucky if I get it spot on. I have just recently sent off a chronometric speedo to Chronometric Instrument Services in Nottingham, who do a complete refurbish, re-calibrate to your requirements for £140 plus £8-50 postage, looking forward to its return now.


I would be pleased to hear what you think of their work once you have it returned and installed.


I've been up to Chronometric Instrument Services, it's a small unit in an industrial complex. Russell, the guy who runs it, is an ex Smiths Instrument engineer and extremely knowledgeable. He worked very hard to get my speedometer working correctly when I plagued with the odometers under reading (by 30 miles on a 90 mile trip) although the speed indication was correct. In the end, it was cured by Russell making and fitting a special 'leaf' spring on top of the ratchet pawl to keep it in contact with the ratchet wheel. Vibration from the engine seemed to be causing the pawl to miss about one tooth in three. Mounting the instrument on rubber grommets and fitting a piece of sheet rubber between the mounting bracket and the top yoke also helped. It now reads correctly, thank goodness.

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Re: Rejuvenating a Chronometric Speedo

Postby 39speedtwin » Wed Nov 07, 2018 10:04 am

I have read with interest the various postings, nearly £150 is very expensive for a refurb!
Also my repairer states that mounting a Chronometric on rubber increases the vibrations.
Also avoid cables that are not from the U.K. as most have the inner above the stop too long, they should be a maximum of 7/16”, any longer and damage to the clockwork will occur.

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Re: Rejuvenating a Chronometric Speedo

Postby Flash » Wed Nov 07, 2018 11:15 am

Well, I have just received my speedo, back from Chronometric Instrument Services for my G9 and what a fantastic job they have done on it, it originally went to them as a speedo from a BSA a10, he rebuilt it and put a new face etc also re-calibrated it for the G9, I am delighted with the end result and will definitely be sending any other speedo I need doing to Russ, three week turn around, I have heard some woeful stories about other repairers but I strongly recommend Russ at Chronometric Instrument Services.

Kind regards Flash AKA TTJohn

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