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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Speedo Irregularities
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<blockquote data-quote="ogrilp400" data-source="post: 41513" data-attributes="member: 88"><p>Dear All,</p><p> Nigh on 40 years of fiddling with Vincents and I still come across things that mystify me. As I wrote some weeks back I am having problems with the indications on a 5" speedo. So lets go through a few things and see where I'm at.</p><p>On the thevincent.com site under instruments are some things listed.</p><p></p><p></p><p>1. "At the bottom of the speedo is a small number(1500 or 1000)"</p><p> I have 5 5" speedos here and two 5" faces. Not one of them has a number at all at the bottom of it. Two of the five are unmolested 1950s' speedos.</p><p></p><p>2. "The 1500 goes with the drive unit marked 15/12 and the 1000 goes with the drive unit marked 2/1"</p><p> I have 5 smiths right angled wheel mounted drive units. All of them are three turns of the input shaft, to two turns of the output shaft. Four of them have 25791 stamped in the bottom plugging plate. The smiths factory information shown on the velobanjogents blog site shows that Vincent only ever used the smiths 25791, 1.5:1 wheel mounted drive units on all the B and C series machines. Only 41/13 drive gears where ever used inside of the brake drum.</p><p></p><p>3. The small right angle drive unit on the back of the 5" speedo is a 1:1 ratio with a 16TPI worm drive and 19 tooth brass gear on it.</p><p></p><p></p><p>So put all this together. My HRD with a 21" front wheel has a working circumference of 81.68". At 60mph the speedo cable will be rotating at 1630rpm. Why is it then that the 5" speedo, at approximately 60mph, is showing 108 mph? I have just had the speedo serviced to sort out this problem and they tell me that they have tested it and it is working perfectly?.</p><p></p><p> Phelps.</p></blockquote><p></p>
[QUOTE="ogrilp400, post: 41513, member: 88"] Dear All, Nigh on 40 years of fiddling with Vincents and I still come across things that mystify me. As I wrote some weeks back I am having problems with the indications on a 5" speedo. So lets go through a few things and see where I'm at. On the thevincent.com site under instruments are some things listed. 1. "At the bottom of the speedo is a small number(1500 or 1000)" I have 5 5" speedos here and two 5" faces. Not one of them has a number at all at the bottom of it. Two of the five are unmolested 1950s' speedos. 2. "The 1500 goes with the drive unit marked 15/12 and the 1000 goes with the drive unit marked 2/1" I have 5 smiths right angled wheel mounted drive units. All of them are three turns of the input shaft, to two turns of the output shaft. Four of them have 25791 stamped in the bottom plugging plate. The smiths factory information shown on the velobanjogents blog site shows that Vincent only ever used the smiths 25791, 1.5:1 wheel mounted drive units on all the B and C series machines. Only 41/13 drive gears where ever used inside of the brake drum. 3. The small right angle drive unit on the back of the 5" speedo is a 1:1 ratio with a 16TPI worm drive and 19 tooth brass gear on it. So put all this together. My HRD with a 21" front wheel has a working circumference of 81.68". At 60mph the speedo cable will be rotating at 1630rpm. Why is it then that the 5" speedo, at approximately 60mph, is showing 108 mph? I have just had the speedo serviced to sort out this problem and they tell me that they have tested it and it is working perfectly?. Phelps. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Speedo Irregularities
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