Smiths speedometer drives
- Thread starter norflog76
- Start date
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.
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.
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- Nov 20, 2004
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norflog76 said:
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.
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.
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.
