Author Topic: Smiths Chronometric Speedo's  (Read 6480 times)

Offline Brucie64

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Smiths Chronometric Speedo's
« on: 13.08. 2009 22:07 »
Just purchased a very expensive authentic Chrono speedo for my Spifire at long last, however I fear it may need a little TLC before it gets strapped onto the bike. The two options are to send it off to a professional to sort out (at even more of a cost) or pull it apart myself to clean and lub. I decided to bite the bullet after reading various posts here and there telling me how easy it is and opted to service it myself.

However, the first problem I have come across is how do I remove the odometer reset knob on the back from it's spindle so I can remove the workings from the case?.

Bruce
Spitfire
UK

Online chaterlea25

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Re: Smiths Chronometric Speedo's
« Reply #1 on: 13.08. 2009 23:28 »
Hi Bruce,
If the reset knob is at the back of the speedo, then its not quite the right model for your bike,
(as far as I know)
Non nacelle BSA's have the reset knob coming out  at around the 5 o clock position pointing towards the rear wheel,
The ones coming out the back are for nacelle fitted bikes, these have a long piece like the outer of a control cable attached to the pin, I think its only forced on over the pin (wound)
the other types have a tiny splitpin holding on the knob.

If the bezel is stuck on, carefully wrap some double sided adhesive tape around the bezel, wrap a length of webbing strap around this (bike tiedown strap) and hold the two ends in the vice
a flat bar with two suitably drilled holes for the mounting stude can be used to unscrew the speedo from the bezel
without damaging the bezel or case!! *smile* *smile*

Beware there are lots of tiny bits in there *ex* *ex*
It takes quite a while to become familiar with the workings of a chrono

Best of luck
John O R
1961 Super Rocket
1963 RGS (ongoing)

Online RichardL

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Re: Smiths Chronometric Speedo's
« Reply #2 on: 14.08. 2009 03:16 »
Bruce,

If you go to http://www.a7a10.net/forum/index.php?topic=680.0 you will see the story of my rebuild and several photos of the guts (hard to find elswhere, I think). Then, if you go to http://www.thevincent.com/vininst.htm and scroll down a bit you will see some good information on cleaning and service.  I have several more photos if you don't see what you need. When the time comes, you will probabaly want to reset the odometer. This can be done by very, very gently lifting the metal tabs (like, with a sewing needle) that prevent back turning, then, rotating the subject wheel into position.

Let me know if there is any other way I can help, after all, I have rebuilt an incredible number of these things, meaning, one.  *lol*  I believe I recall that others here have rebuilt multiples, so you can certainly get the help you need, once inside the casing.


Richard L
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline a10gf

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Re: Smiths Chronometric Speedo's
« Reply #3 on: 14.08. 2009 09:49 »
off topic
Richard, excellent speedo post from 2008, I've not seen if before!
e

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Offline Rusty nuts

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Re: Smiths Chronometric Speedo's
« Reply #4 on: 14.08. 2009 10:32 »
I decided to bite the bullet after reading various posts here and there telling me how easy it is and opted to service it myself.

Don't want to put you off but my brother is a horologist (clock & watchmaker) & he wouldn't touch mine!
He is exceedingly lazy though.
I found a couple of articles on the web:

http://www.hells-confetti.com/Technical%20data/Jaeger%20Instruments/Jaeger%20Chronometric%20Overhaul.pdf

One from the classic Motorcycle 1992 clear instructions lots of pics see below.
 This web page very slow to load can appear as broken link.
 and another good one here  http://pcbunn.cithep.caltech.edu/jjb/TR6/speedo.pdf (More for car speedos TR6' & 4's but still some interesting technical stuff)

If you find something broken or it needs more than a clean & you decide it's beyond your abilities I can highly recommend David Woods here in West Sussex:
http://www.chronometricspeedos.co.uk/index.html

1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

Offline Brucie64

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Re: Smiths Chronometric Speedo's
« Reply #5 on: 15.08. 2009 08:33 »
Speedo all done (ish), dismantled/cleaned & lubed. The speedo runs up to around 76mph when run from an electric drill in reverse which is a vast improvement than before it was done.
It wasn't a totally successful venture though, I tried literally for hours to screw the chrome bezel off but to no avail. In the end (and to stop damaging the speedo casing) I decided cut the bezel off with careful strokes with a miniture hacksaw, 2 minutes and it was off with no damage to the rest of the speedo.

Question is does anyone know where can I get a replacement 80mm chrome bezel for a Chronomentric speedometer?
Bruce
Spitfire
UK

Offline Rusty nuts

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Re: Smiths Chronometric Speedo's
« Reply #6 on: 15.08. 2009 09:39 »
Had to do same with mine completely corroded on.

David Woods see link above has them £10 - £15 depending on the quality you want.
Also has rubber seals etc.
1949 A7 Plunger
1947 A7 Rigid Star Twin
1969 Triumph T120R
1972 Triumph T120V

Offline Goldy

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Re: Smiths Chronometric Speedo's
« Reply #7 on: 16.08. 2009 19:03 »
There are two things that I would never touch on a motorcycle. One is wheel building and the other is the Speedometer. I took mine to http://www.speedograph-richfield.com/ Excellent repair clean and re calibrate. I understand that they were once part of Smiths. Regards.
56 A10 Golden Flash - Restore, ride, relive.                                          
56 C12 BSA project ongoing

Offline Brucie64

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Re: Smiths Chronometric Speedo's
« Reply #8 on: 20.08. 2009 16:09 »
Does anyone know how accurate chronometric speedo's should be?.

I measured the speed of mine against a Sat Nav strapped to my tank and found the speedo to always show around 5-8mph slower than the Sat Nav.  I am sure that the Sat Nav will have some degree of inaccuracy but on the whole is this level of descrepancy acceptable or should I be looking at getting the speedo calibrated?
Bruce
Spitfire
UK

Offline alanp

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Re: Smiths Chronometric Speedo's
« Reply #9 on: 20.08. 2009 16:38 »
Unless I was broke, I'd send any in need of tlc to David Woods. Guys like him can spot worn parts and replace them which most of us can't. Yes, we can clean up, reset mileage readings etc (I've done that myself) but come on chaps these things are ancient and need professional eyes and facilities or it will develop the dreaded needle wobble or some other disease we've all seen and need their expertise sooner rather than later.
Member of the 'Last of the Summer Wine Club - Jennycliff'.

Online RichardL

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Re: Smiths Chronometric Speedo's
« Reply #10 on: 20.08. 2009 17:18 »
I agree with Alan regarding changes to the internals, but you can figure out for yourself if you have the correct unit by matching your rear-wheel turns per mile to the speedo turns per mile based on the ratio at the gearbox. I did my best to figure this out for my own speedo, and that attempt is described at http://www.a7a10.net/forum/index.php?topic=701.msg4399#msg4399.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline Beezageezauk

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Re: Smiths Chronometric Speedo's
« Reply #11 on: 20.08. 2009 20:17 »
Hi Bruce,   I see that you are from the UK.  OK...an accurate way of checking your speedo is to find one of these villages with a speed sign that flashes up if you are over the speed limit.  You know the ones I mean??  If the speed limit is 30mph and you are doing 31 it will make it clear that you are going too fast and warn you to slow down.  If you are doing 30mph it remains dormant.

All you need to do is approach the sign at a slow speed then gradually increase the speed on re-runs until you know what your speedo reading is when the sign flashes and tells you to slow down.  You then know when you are doing 31mph and can compare your speedo reading.

Maybe non-UK members can advise if these machines are in use in their own country? 

Beezageezauk.


Offline MikeN

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Re: Smiths Chronometric Speedo's
« Reply #12 on: 20.08. 2009 23:25 »
If you decide to get your speedo re-callibrated ,I know that Dave Woods will ask you to carry out the following so that he can set it up corectly:
a)Unscrew cable from speedo head and attatch a pointer to the end of the inner cable.A little flag of masking tape will do.
b)Check correct inflation of tyres
c) sit astride bike on road and get an assistant to put a chalk mark at the 6 0clock position on the rear .tyre and a corresponding mark on the road.
d) Get assistant to push bike with you sitting on it (important for an accurate result) one full rev of the wheel whilst counting the revs of the cable pointer.
e) mark road after 1 rev with chalk.
f) Using a tape measure ,measure the  distance travelled and make a note of the cable revolutions.
For greater accuracy you could do (say ) 4 wheel revs then divide your results by 4.but you need a longer tape measure.
 This is the way Woodsy told me to do it.I must get round to it someday,as my speedo is way out.
Mike

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Re: Smiths Chronometric Speedo's
« Reply #13 on: 20.08. 2009 23:26 »
HiBruce
Chrono speedo's should be extremely accurate!
However there are many factors that affect the gearbox driven on BSA "A's"
Gearing/ sprocket sizes
Tyre sizes,pressure  and even tyre wear affect the speedo and milage readings
If you buy a cycle speeo/computer and calibrate this to the tyre circumference
you will be easily be able to compare it to the chrono
I measure the circumference by putting a spot of tippex or white paint on the tyre, sit on the bike and roll forward a couple of revolutions of the wheel, measure the distance between the paint spots and enter this value to the cycle computer.
Compare the readings at various speeds, if the difference is more or less the same through the range you can re position the needle to correct the difference, the needle is on a taper but be careful pulling off the needle as the spindle is hollow and a normal (pressure gauge ) needle puller cant be used.
I use a thin piece of steel with a narrow slot in it this can be hooked under the needle boss and pop it off
HTH
Regards
John O R
1961 Super Rocket
1963 RGS (ongoing)