Smiths Chronometric Part Numbers

[simon.holyfield]

Folks,

Casting around the net, we can find lists of Smiths speedos and their application to motorcycles relatively easily.

But can anyone shed any light on what the Smiths part numbers actually mean? This might help us find speedos which are a close equivalent to ones which are actually designed for our machine, when the likelihood of finding exactly the right one is pretty small...

[david.anderson]

The speedo on my 49VH is original (with original face) and carries the numbers S 467/11/L. The speedo on my 57VH has the numbers S 467/195 which I believe is correct.
Most speedos now have been rebuilt and to justify the money for the rebuild a new speedo face sticker is attached. Many of the new faces have no numbers or a wrong number is stuck on by the repairer as he doesnt have the vast array of stickers necessary. I have a couple of chronometric speedos on Ariels with the wrong numbers but they still display the correct speed.
There is another number that some chronometrics have which represents the number of turns of the speedo cable per mile. Some MGs have this number below a line and I have seen a separate number on a couple of BSAs ( to the right of the main code no and it was 1500 and in another instance the number was above the word 'chronometric'). The attached photo is of a 48NH that has a rebuilt speedo. It shows the number 1600 above the main code number on the new face(that number was not there on the original dial). Being a rebuilt speedo I cant guarantee that it is the right sticker for the speedo but the speedo is accurate. It is the only speedo I have that includes the most important number of all (if it is right)

[david.anderson]

just found a bit more info on speedos. According to Waller all chronometric speedos for ariels should be 1610 turns of the cable per mile, so any chronometric with 1600 on the dial should be right. When I had my 48 NH speedo done up the repairer clearly had a suitable sticker. A PA speedo should be 2240 turns per mile.
David

[Bernie Blundell]

Just to add chronometric speedo for leaders are 1584 TPM

[Chris Sealy]

Just for interest. As with all mechanical speedos, the Chronometric is really measuring revs per minute, of the cable connected to it.
The clever thing about it; is that you can trim the reading on the dial by adding or subtracting weights to the balance wheel.
When in use, the balance wheel oscillates under the control of a coiled spring. The heavier it is, the slower it oscillates.
The balance wheel is at the left side of the picture, with the weights clipped to the shaft above it.