Sunday, September 5, 2010

The Vincent speedometer.....

Posted by car 2011 at 8:01 AM

Throughout my various earlier blogs there are references to chronometric speedometers and tachometers and of course I have showcased Phil Irving's involvement with The Vincent Motorcycle.
So perhaps this is the time to post some data of the Smith's instruments and ancillaries used on the Vincent motorcycle.
All the Vincent speedometers used on the 500cc and 1000cc models were Smith's chronometric instruments, including the tachometer on the Black Lightning and Grey Flash racers.
Prewar the cable fitting attached to the speedo via what is called in the instrument trade "a Jaeger fitting". The threaded fitting came during WW2 and used a 12mm x 1mm thread.
Interesting the use of metric threads...but the chronometric is a French Jaeger instrument and thus totally metric.
Left click on the images to enlarge.

In the 1930's most of the chronometric speedometers supplied to the motorcycle trade were 80mm ( 3") diameter 85mph often Non trip, but otherwise trip and 140kph for metric areas of the world. But some did use 120mph, such as the Rudge Ulster, the BSA Gold Star, Brough Superior and the Vincent "A" twin . I don't have evidence for the single 500cc Meteor, but would be inclined to think it used the 85mph/140kph speedo.
After WW2 the trend for 85mph speedos continued up until around 1949 with many manufacturers, but Vincent-HRD, then just Vincent used the 120mph trip chronometric with side exit trip as the speedo was mounted in the open.
Note above the Smiths logo...we call this the shield logo and it was used up until the mid 1946, when the circular "MA" was removed and the text became SmithS with the "S" at either end in capitals.
From the mid 1950's, but more likely 1959 on, the logo was SMITHS...






Following WW2 the Vincent-HRD company used the following for the series B and series C Comet and Rapide.
With the imminent introduction of the Black Shadow, PEI recalls on p.365 of his autobiography the need for a 150mph speedo with a 5 inch dial.
This is one of the available photos that show the prototype speedometer, published in the Australian motorcycle magazine "Motorcycling in Australia"
I do not know how many of this "lashup" of a speedometer were made.
But the cast aluminium version, stove enameled black is a nice looking speedo.
The following are photos of the reproduction of the original I still make.
The speedometers were available as 150mph, but in metric areas, a 250kph version was offered.
Around the same time a racing version , the Black Lightning, made in very limited numbers was supplied with an 8000rpm 4-1 ratio anti-clockwise cable rotation chronometric tachometer with yellow lettering and some had speedometers...a 18omph  80mm (3") dia. chronometric or a 280kph 80mm (3") chronometric for the minuscule number available for metric areas. Again yellow lettering.
A racing version of the 500cc Vincent Comet, called the Grey Flash was also supplied with an 8000rpm 4-1 anticlockwise Smiths chronometric tachometer and was offered with a 125mph or 180kph speedometer with white numerals.
Both the Black Lightning and the Grey Flash used a Smiths bronze casting tachometer drive type 70549 of 2-1 ratio and reversing format.


The reason for the special anticlockwise tachometer was that the majority of British motorcycles drove tachometers off their magneto and when you looked at the shaft which the drive gear attached to, it rotated anticlockwise.
Smiths only offered the bronze type 70549 tachometer drives in 1-1 reversing and 2-1 reversing.
So with the Vincent having a clockwise rotating magneto, the use of the 2-1 reversing tachometer drive gave the 4-1 anti-clockwise tachometer requirement.
When the fully enclosed models arrived in the mid 1950's...the Victor, Black Knight, Black Prince the speedometers were all 80mm ( 3") dia. but as they were in a dashboard, they had flanged bezels and and extended reset shaft. The Victor and Knight has 125mph/180kph dials and the Prince 150mph/240kph dials. 
The speedometers had a small angle drive on their back of the same type as the earlier Black Shadow, but with a keyplate and two 4BA screws to secure it to the case.
Finally the drive to all the speedometers was from the pre WW2 type front wheel diecast speedometer drive gearbox in the brake plate with the driver gear bolted inside the front hub.
These small diecast drives are 1.5-1 ratio. The large gear was 41 teeth ( same as a Velocette KSS and MSS) . The small driven gear was 13 teeth ( again same as Velocette KSS and MSS) both 12 D.P. tooth form.
The front wheel "nominally" turns 750 times in a mile. 
This is calculated as follows....
21" wheel with 3.00 tyre, gives a diameter wheel/tyre diameter of 27".
C=pie x d...3.142 x 27 = 84.8" rolling circumference.
1 mile = 63,360 ". 
So 63360/84.8 = approx 750 wheel turns per mile.
The two gears give a 41/13 = 3.15 ratio and the 1.5:1 reduction in  the drive gives a total ratio of 2.1:1.
So 2.1 x 750 = 1575 cable turns per mile calibration factor. 
Most of the speedometers were available as 1550 to 1600 TPM.
Now I may come back and amend this blog, as it is after midnight as I post it...
The Black Shadow never had a 5" Smiths chronometric tachometer as standard, but some time after the Vincent company went into liquidation and closed after 1955.....5" diameter  8000rpm tachometers in the cast speedometer case became available in limited quantities.
I have have also made them and illustrated below is one , with the bronze type 70549 drive for a customer.
Following are some Smiths Equipment Schedules for Vincent which give instrument, drive and cable information as supplied to the Vincent Company.


Speedometer cable lengths to 1948.





































 

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