Tach drive ratio

[medat727]

Hello, can anyone tell me what the Rapide tach drive ratio is, 2/1, 4/1, etc.

Thanks

 

[davidd]

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]

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]

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]

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]

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]

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]

Dear Mr. Hutch,

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

David

 

[mr.hutch]

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