This covers the instruments introduced with the BMW/6 models in late 1973 for the 1974 season.
Initially the R60/6, R75/6, R90/6 it was followed by the R60/7, R75/7 then R80/7, R100/7 and with the introduction on the monoshock rear end the R80, R100.
The mechanical tacho was used from 1974-1977.
While still a black background, the colour of the numbers/text changed from white to green.
As well the 52mm dia. clock that was available changed from an impulse type to a quartz type.
So the dial colour is a good dating mark.
The speedometers were 140mph for imperial areas such as the UK , USA and 220kph for all the metric areas.
There were some 85mph speedos made for the USA market during the Reagan era in an attempt to slow vehicles down.
The ratios for the speedometer which relates to the final drive used is marked on the dial as w=xxxx. For example with a 32:10 rear drive in a Km speedo it would be w=0.737 and w=1.186 for mph speedo.
What this means is that for the km. speedo, the inner cable rotates 737 times for one km.travelled.
So if the cable rotated at 737rpm, the speedo would show 1km/minute which is 60km./hour.
You'll note they show a large nut on the speedo and tacho mainshafts where the drive cable attached.
The threads are... speedo 18mm x 1.5mm and for the tacho 16mm x 1.0mm.
These nuts were designed to lock back down onto the cable nut, presumably to stop the cable nut unscrewing.
But in all my years in the instrument trade this was never a problem and in fact causes a problem with these Motometer instruments over time.
It becomes difficult to undo them.
So my advice is to remove them completely..they are unnecessary....
From 1978 the speedo use a plastic bushing for the mainshaft to rotate in.
Detail of the speedcup shaft bottom pivot length. This wears on the end stone in the bush at the top of the mainshaft and the inside of the aluminium speedcup "poles" on the magnet, eventually destroying it.
You can lightly stone the worn end of the shaft and then tap it though the brass piece in the speedcup to the correct setting...0.140" protruding.
From DQs notebooks...electronic tacho calibration information.