Smiths speedometer drives

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Dec 26, 2006
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I see from previous posts that some of you have taken considerable time to figure out and document which instruments went on which model bikes.

Does anyone know which smith speedo drives go with which speedometers?
 
Joined
Dec 26, 2006
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And the silence was deafening!

I measured the rear tire circumference and made some calculations with the following results:

If using a Smiths speedometer with the number 1600 following the part number, use a speedometer drive with the ration of 2/1.

If using a speedometer with the number 1000 following the part number, used a speedometer drive with the ratio of 15/12.

I am using a "1000" on the featherlastic, and with the rear tire being used, the 15/12 ratio drive results in a 3.5% speedometer error.
 

L.A.B.

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norflog76 said:
And the silence was deafening!

Sorry I did intend to reply sooner!

However...

All Commando MPH drive gearboxes were (as far as I can tell from the parts books) 15/12 (1.25:1) ratio, as the Norton drive gearbox part number (060627) was the same from 1968 to 1974 although the very early KPH (060733)speedo used a different drive gearbox (030208) and by 1971 (or possibly earlier) there was only the 06-0627 drive box listed, so it would appear that a different type of KPH speedo was then used with the the same drive box as the MPH speedos? The known KPH speedo types being: 600 (cable) turns = 1Km, and the MPH speedos: 1000 turns = 1 mile.

The Smiths number stamped on one of these units I have is: BG5330/171. I don't know if all 060627 numbered drive boxes were *171* type or not -unfortunately.

The 850 Mk III used a different (065540) drive unit mounted at the left-hand end of the rear wheel unlike all earlier types.
 
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Thanks L.A.B.
You are probably correct on the Commando speedos/gearboxes, but when you're digging through that box of parts in your shed or at the swap meet (autojumble in your case), you might find a good speedo marked as a 1600 (as I did). It's good to know that it can be used on a Commando if the appropriate gearbox is used with it. Many 1600s were used on BSA, Triumph, and Atlas. So what if it only goes to 120 MPH? I've never had a Brit bike over 120 MPH.

I'll put your speedo info in my info bank. It's quite useful when one wants to do a proper restoration. Have never before seen a summary of instruments for Commando in any of my reference books.
 
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