Rejuvenating a Chronometric Speedo - PHASE 5

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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby clive » Fri Oct 04, 2019 5:58 pm

SPRIDDLER wrote:Such skill! I wouldn't have the courage to fiddle with one.
Great Youtube clips too which convinced me that out of all the engineering on our old bikes the chrono speedo is far and away the most complex, precise and sophisticated part. You can't restore one o' them with a Helicoil or a pair of Mole grips. :(

Very true Sprids. I once counted the parts in a standard Chronometric with trip and established there were more parts than in a single engine, although i think i counted the big end and main bearings as a single unit rather than counting all the balls or rollers separately.
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby Group Leader » Fri Oct 04, 2019 7:25 pm

Thanks chaps for the comments :beer:

I assembled the odemeter and tripmeter drive this afternoon and there discovered a trap for the unwary (that'll include me!).

In this fine article http://www.wdbsa.nl/Jaeger-Chronometric-Overhaul.pdf it states;

"Undo the outer locknut, and unscrew the 7BA bolt from the inside. The order, which can be seen in the photo-graph, is bolt; brass shim; pawl to tripmeter, with spring; eccentric wheel and spacing washer; odometer pawl and spring; driving gear and pin; brass shim; supporting pillar on base; outer plate with pin which takes the two pawl springs; and finally the locknut."

I didn't realise the pin was there when I disassembled it and it certainly wasn't when I went to re-assemble it! So I had to do a bit more turning and produce a new steel pin ~5mm long and 0.9mm diameter. I made one end very slightly larger to provide an interference fit in the brass gear. The pin locates in a hole in the eccentric bush and provides the drive to it. Still, I got away with that one :) Actually, I found the trickiest bit of the re-assembly was getting the ends of the two pawl springs on to the retaining pin but I managed it in the end.

The speedo has now been re-assembled and put back on the bike. It would have been rude not to go and test it particularly as it looks like a wet weekend is ahead. That's a bit of a shame, as I was going to go to the last Shuttleworth Air Display of the season, themed "Race Day" it includes cars and bikes. Maybe I'll have to re-consider my plans.

Anyway, it all seems to be working nicely now so I'll give it a few miles and then I might sneak a look inside just to make sure things are still OK.

Alan
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby clive » Sat Oct 05, 2019 8:56 am

Alan if its working leave it alone til it goes wrong!
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby Group Leader » Sat Oct 05, 2019 1:39 pm

clive wrote:Alan if its working leave it alone til it goes wrong!


You might have a point there!
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby Martin.S » Sat Oct 05, 2019 11:00 pm

I disagree - periodical maintenance - a clean and a light lubrication

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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby clive » Sun Oct 06, 2019 6:43 pm

Group Leader wrote:
Anyway, it all seems to be working nicely now so I'll give it a few miles and then I might sneak a look inside just to make sure things are still OK.

Alan


Martin this was the reason for my advice, given that Alan had missed the pin during his disassembly.

Having said that the most usual fault when I used to fix speedos was lubrication in the slipping clutch. Usually caused by oil lubrication of the speedo cable, or sometimes too much grease. The cable drives it into the speedo through acting as an Archimedes Screw. If you lubricate it does need to be very light.
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby SPRIDDLER » Mon Oct 07, 2019 5:49 pm

clive wrote: If you lubricate it does need to be very light.

Is that Mono or Multi, Clive, and what grade do you recommend?

(Well you did post that you're bored waiting for the girls walking the Camino trail. ;) )
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby markwhitelock » Mon Oct 07, 2019 6:32 pm

This has been a really interesting thread, It appears that the speedo is a very complicated part of the bike!

My Smiths speedo has definitely seen better days, I can’t get the trip to reset and the drive cable is missing so I have no idea if it works (I very much doubt it). I am lacking confidence in trying to rebuild it as described here so was wondering what short term fixes are available that don’t look too out of place (I did consider a magnetic bicycle speedo!). Looking on the internet there are Smiths lookalikes from anywhere from £15 up to a few hundred for an original, what have people done who have had to replace a broken speedo?

I should add that mine is in kilometres per hour and I would prefer it to read in miles per hour for ease of use. Is it possible to change them over if I do get it working? Is it a case of changing gearing at the rear wheel mechanism or in the speedo itself?

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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby Group Leader » Mon Oct 07, 2019 9:12 pm

markwhitelock wrote: I can’t get the trip to reset and the drive cable is missing so I have no idea if it works (I very much doubt it).

To be honest my trip reset is just about unuseable, the spring that you have to overcome to engage reset drive seems ridiculously strong although I've not really looked into why that should be so far.

You can check basic function of the speedo by removing it from the bike and finding a small, square section shaft matching the speedo drive (unlikely but not impossible) or a small (eg jeweller's) screwdriver whose blade is a good fit across the diagonal corners of the drive (far more likely) and inserting either into the speedo drive and rotating it anticlockwise looking at the back of the speedo. If you rotate it between your fingers you can get a twitch maybe up to 10-12mph. If you have a reversible, battery electric screwdriver/drill you can drive it more consistenntly probably upto 30mphish. Either way will show whether the basic instrument is functioning.

markwhitelock wrote: ... here so was wondering what short term fixes are available that don’t look too out of place (I did consider a magnetic bicycle speedo!). Looking on the internet there are Smiths lookalikes from anywhere from £15 up to a few hundred for an original, what have people done who have had to replace a broken speedo?

I believe the very cheap lookalikes are best used as doorstops (and they are not even very good at that as they are probably too light). The reviews/reports I've seen have not been very complimentary and they all appear to be short lived. As to the more expensive lookalike versions, I don't know how good they are or not. If I was going to lash out a few hundreds I'd look for a proper, fully functioning but cosmetically poor original in preference. You can buy a complete replacement body/glass/bezel/seal for ~£35 which is exactly what I've done for my own "Faux Chronometric" electronic speedo that I'm building for my little Beezer 250 project that has no drive for a proper chrono. It uses a couple of rare earth magnets mounted on the front wheel in a similar style to the digital push bike speedos you mentioned.

My speedo is still under development but perhaps I should go into production when it's done! :o

For interest, here are a couple of videos of it being tested; the first shows it on the Beezer the second shows it on the left alongside the proper one on the right on my AJ. To test it on my AJ I just stuck the rare earth magnets to the wheel rim and positioned the sensor accordingly. As you can see, it's still work in progress (just like the rest of the Beezer).

https://www.youtube.com/watch?v=4tPon8KCs74

https://www.youtube.com/watch?v=eU4mqohViyA&t=49s

Of course, you could get yours restored to working order professionally for a similar amount as a proper replacement.

markwhitelock wrote:I should add that mine is in kilometres per hour and I would prefer it to read in miles per hour for ease of use. Is it possible to change them over if I do get it working? Is it a case of changing gearing at the rear wheel mechanism or in the speedo itself?

You need to change the rate at which the odemeter and tripmeter count so I should imagine that's done at the rear wheel end, you obviously also need a re-calibrated dial and possibly to slightly change the sampling period of the speedo section which would be gears in the speedo itself. I'm just guessing here, hopefully more knowedgable types (Clive, where are you?) can confirm or contradict as appropriate.

Alan
Last edited by Group Leader on Mon Oct 07, 2019 9:21 pm, edited 2 times in total.
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Re: Rejuvenating a Chronometric Speedo - PHASE 2

Postby Pharisee » Mon Oct 07, 2019 9:17 pm

markwhitelock wrote:I should add that mine is in kilometres per hour and I would prefer it to read in miles per hour for ease of use. Is it possible to change them over if I do get it working? Is it a case of changing gearing at the rear wheel mechanism or in the speedo itself?


They can certainly be recalibrated. I've had a couple rebuilt by Chronometric Instrument Services in Nottingham. Russell can pretty much turn any Smiths chronometric into whatever you want. It seems to be a case of changing gears and dials. The rear wheel drive stay the same. Speedometer into a tachometer is not impossible. [EDIT]... not driven from the rear wheel, of course. You would need the correct gearbox driven from the engine.

http://www.chronometrics.co.uk/

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