Author Topic: Smiths Speedo Drive  (Read 293 times)

Offline ramwing7

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Smiths Speedo Drive
« on: September 26, 2020, 04:25:59 PM »
Can anyone tell me if all the Smith's speedometer drive gearbox are the same for all BSA, Nortons, Triumphs, etc.?
Thanks.

Offline Mark M

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Re: Smiths Speedo Drive
« Reply #1 on: September 26, 2020, 04:44:21 PM »
Yep, they aren't. Variations include drive cable exit above or below the wheel spindle, spindle hole size (usually larger on heavier bikes,) and crucially, gear ratio. Most British bikes used a standard 2:1 ratio but there are numerous other variations. On later boxes this will be stamped onto the circular keeper plate that holds the ring gear in place but can only be seen when the box is off the wheel. Earlier models (up to about 1961?) were a different shape, rather square in section, and have the part number stamped on the brass plug that retains the small worm gear. These do not have the ratio on them.
REgards, Mark

Offline R

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Re: Smiths Speedo Drive
« Reply #2 on: September 26, 2020, 11:21:03 PM »
If this is for your Electra ?, you need to study the parts book to see what Smiths speedo drive AND SPEEDO was specified.

Somewhere about then, speedos switched from chronometric (clock mechanism) to magnetic type, and the speedo
drives switched from generally being 2:1 ratio to 12:15 ratio.
The numbers on the speedo face will tell you what you have, and need in the way of speedo drives, but need some interpreting.

Be aware that India now supplies a vast range of replica stuff, but you need to be sure what you need for it all to work together,
they supply a number of varieties that are not entirely equivalent to what used to be supplied.
Beware in particular of 12mm fittings on cables and speedos, this is a new standard and must all be matched.

Offline Rex

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Re: Smiths Speedo Drive
« Reply #3 on: September 27, 2020, 08:38:32 AM »
The Indian stuff looks OK if you just want to fill the space where a speedo should be, but as the speedo heads are all magnetic the cable entry is central unlike Chrono heads where the cable entry is off-set, and this causes fitting problems for some bikes.
I wasn't aware that the Indian stuff had any variables with regards to ratios etc, and in my (thankfully limited experience) they only have two settings, new or fecked, and with a month's gap between the two.
But then for twenty quid.... :-\

Offline Mark M

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Re: Smiths Speedo Drive
« Reply #4 on: September 27, 2020, 09:31:28 AM »
Yes, Rex is right about the cables being different. Fortunately Hitchcocks Motorcycles sell a selection of lengths with the correct Smiths fitting at the drive end (rear wheel) and the appropriate Metric (12mm?) fitting at the instrument end. He is also correct about the cable entry point on the Indian speedometers but they are also deeper in section than either Smiths Magnetic or Chronometric units which might be an issue on some makes, especially if it's mounted in a headlight shell.
REgards, Mark

Offline L.A.B.

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Re: Smiths Speedo Drive
« Reply #5 on: September 27, 2020, 02:09:13 PM »
According to the Smiths list, the correct speedo drive gearbox for a Norton Electra would be a 2:1 reversing BG 5330/257.

The speedo would be an SSM 2001/02 and 5ft. 2 inch DF 9110/00 cable.
   
L.A.B.

Offline R

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« Last Edit: September 29, 2020, 10:00:20 AM by R »