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Tach drive ratio

davidd

Well Known and Active Forum Website User
VOC Member
Medat727,

The tachometer should be a 4:1, anti clockwise. RC.103 is the original for production Flashes and street twins. It is an 8,000 model. A good chronometric repairman can convert a 2:1 clockwise.

David
 

medat727

Well Known and Active Forum Website User
VOC Member
Thanks for the info, can I assume that the tach drive itself is 1/1, one turn at the rev counter drive dog equals one turn at the cable?
 

davidd

Well Known and Active Forum Website User
VOC Member
There is a 2:1 angle drive on the ATD cover that when combined with the 4:1 tach head reads correctly. If you need info on the tach drive it is in Know Thy Beast, Figure 23, I believe.

David
 

mr.hutch

Well Known and Active Forum Website User
VOC Member
Quite correct David,
pages 189-190 of the third edition.
Just out of interest though, I have always had a 1-1 ratio gearbox on the outfit, all I do is halve the reading on the dial, which happens to have yellow numbers, needle etc., RC115 on the dial. These were quite common I'm told although I have never come across a similar one.

go carefully mr hutch. :)
 

davidd

Well Known and Active Forum Website User
VOC Member
Thanks for checking my work as I was doing it from memory. I would not have called the RC115 common, but I was not around when they were! It is lovely to have an origianl Black Lightning tach.

David
 

mr.hutch

Well Known and Active Forum Website User
VOC Member
Hi David,
thanks for the response, are you saying that the Smiths RC115 was sort of exotic like lighning stuff?

go carefully mr hutch
 

davidd

Well Known and Active Forum Website User
VOC Member
Dear Mr. Hutch,

Yes I am! Did you notice an increase in power when you mounted it?

David
 

mr.hutch

Well Known and Active Forum Website User
VOC Member
As it has been fitted since day one, I can't say, but maybe if I disconnect it there should be a marked loss of power? I will experiment.

go carefully mr.hutch

Dear Mr. Hutch,

Yes I am! Did you notice an increase in power when you mounted it?

David
 
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