murph wrote:Well to see if this can bring up an interesting conversation I know nothing about, and due to Dave's recent post in the craigslist finds let's see what we get.
I know for a fact that my restored 1962 xlch with late vin has an original chronometric nos tach from harley davidson on it because I bought it on ebay in its original box with all the mounting hardware. The RC# on the dial reads 1302/00.
I also had an original paint 1962 xlch which was in my possession some time ago which also had the factory chronometric tach and interestingly enough the vin # was only off 6 digits from my restored 62. This also had an RC 1302/00
Now with all that said here is my original paint 1959 xlch that has the chronometric tach on it as well, yes I KNOW they never left the factory with the tach in 59 but the original owner did this prior to Harley Davidson and that's how the bike is staying. It's tach has an RC 83 on the dial. My question is What are the differences in the tachometers? My guess is ratio?
https://www.harleykmodel.com/gallery/19 ... index.html
a primer of escapements, hair springs, and timing of those:
cronos tachs dont have a 'gear ratio'.
instead they work by engaging/disengaging the indicator needle to the drive cable.
when the needle jumps (up or down) its connected directly to the cable rotations.
when the needle rests between jumps in disconnected from cable rotation.
so the when the connection time is great so is the needle sweep.
varying the connect-disconect time varies the needle sweep amount.
so given that you can print different background faces with different speed ranges.
print on the that face a code that says what the connect vs the disconect should be for a given cable rpm and you change the escapement to match.
escapment is time engaged vs time disengaged
so
for a given cable rotation rate (motor rpm) the tach needs to be calibrated to engage/disingage the needle rotation.
what cant be changed is that the needle rotation direction follows the cable rotation direction.
as far as the rotary orientation the face and needle thats easily set on assembly.
things change when talk goes to speedos.
for the odometer to be accurate the cable rotation per mile needs to be correct.
speedos faces will say how many cable rotations = 1 mile
then the escapement is calibrated to match 1 mile of cable rotation in 1 minute to 60 mph.
this is skimming of the whole picture.
those who want to fix old cronos-- the problem is allways the same. sourcing the small "swinging" pinion gear
i have no answer for this at the moment.