Joined: Sep 2002 Posts: 7,812Alex
BritBike Forum member
BritBike Forum member
Joined: Sep 2002
Your bike would originally have had a grey-face chronometric (SC3313/00 in miles, SC3313/00 in km), but those are pretty rare. Your best route is probably to find a useable chronometric speedometer and have it rebuilt with a reproduction face and the correct ratio. I don't remember the correct ratio off the top of my head, but I believe 1600 revs/mile (1000 revs/km) is correct.
A smattering: '53 Gold Flash '67 Royal Star '71 Rickman Metisse '40 Silver Star '37 Rudge Special sixtyseventy Lightboltrocket road racer...and many more.
Your gearbox ratio is much the same as the rear wheel gearbox ratio of 2:1 which means the speedo needs to be a 1600 revs per mile or 1000 per km as the rear wheel does 800 revs per mile or 500 revs per km. Not seen an aftermarket speedo covering that ratio.
Sorry to hijack this thread, but as it is rather convenient, I'll ask about this here.
Can anybody tell me how to tell apart chronometric an magnetic speedometers? I have a speedo that says "S.467/59/L CHRONOMETRIC SMITHS M.A. MADE IN ENGLAND" on the face. However, if I was asked, I would say the clock is operated by some kind of a magnetic system. Is the chronometric speedo mechanic, do I have some kind of a replica?
The speedo shows speed readings that are total nonsense and the odometer gives distances in miles that can be converted to kilometers By a coefficient of approximately 2,6 and it seems to work this way rather consistently.
Judging by the behaviour of the odometer it's easy to come to a conclusion that the speedo drive on the rear wheel hub might be too slow, but AFAIK this very clock has previously worked with an original Smiths 1,25:1 drive, which has since been replaced with a repro. Besides, wouldn't a 2:1 drive be even slower?
Last edited by Beezaster; 05/17/151:56 pm.
Some of them call me "Teddy"
'71 A65 Thunderbolt "The Killer Bee" (Also the frustrated owner of a Triumph Spitfire 1500)
Right, well there's definately no clockwork inside my speedo, so a knock off for sure. The drive gearbox is probably the wrong one, but even so, the speedo should still work logically, just giving too low readings. I went a short strech flat out in fourth gear last night and as I looked down at the speedometer it showed a steady 10 mph. I don't think that's correct.
I'm thinking of getting magnetic replica clocks (no tacho at the moment), but are they any good or just a waste of money?