Ratio Rev Counter

[Pan47]

Hi,

the ratio that i mean is 1:4 1:2 or 1:5

You can read this sometimes on the display of the revcounter,

Never hear ratio definition 20;3

The master question was what ratio has the serial original cb77 revcounter.

[/b]I can't believe that nobody in this forum now this.

Christian

[DJM]

20:3 IS the correct ratio for the CB77 and most if not all Japanese lightweights.

The figure appears on the dial of some instruments and is in the Shop manual for my CB72 since 1960 so I know it is correct.

[Pan47]

Hi,

means that 20 rev from the crank makes 3 rev on the cable?

Or 3 rev on the cabel makes 20 revs on the Display?

We have the revs on the crank than the revs from the gear on the enginehead and at last the revs from the gear in the revcounter.

Oh my good

[DJM]

Well actually both,

(Say) 2000 revolutions (per minute) of the crank becomes 300 revolutions per minute on the cable.

Then the reverse happens in the instrument, 300 revolutions per minute on the cable shows up as a reading of 2000 revolutions per minute.

The reduction ratio is just there to keep cable speeds within sensible limits.

Big British bikes (small ones rarely had rev counters fitted) were slower revving so a reduction of 2:1 or 4:1 was enough to keep cable speeds low.

Higher revving Japanese engines needed a higher reduction ratio 20:3 or 6.666:1 to keep cable speeds down.

If you can get a 7:1 instrument that will be close but the rev counter will actually read around 5% slow. Probably near enough, many rev-counters, aren't that accurate (within 10%) anyway. Hope this helps.