mk1-forum.net

Hi All. When refitting the centre part of the speedo do you lift the needle above the speedo stop pin? Not sure if you have to wind it round at all and missed that when I dismantled it. Even google and youtube can't help me on this one....

On some Smiths speedos there is a faint line or dot printed on the face before the zero stop. You fit the needle so that it points at the line or dot with the mechanism relaxed, then you either lift it over the stop or take the stop off and position the needle past it. This should give the correct amount of amount of pre-load to the spring and make certain that it always homes back to the zero stop.

Tim

Hallelujah! Thanks Tim. I cannot believe the lack of replies on this one. The internet has next to nothing on this subject either which is really frustrating especially as the old speedos are getting what you might regard as rare nowadays. Many thanks and if anybody else has anything to add please let me know. Best wishes. Mark

tim is correct that the spot below the pointer stop should be used as the reference for absolute zero if it is there.
You cannot calibrate an instrument uless you have the zero point correct in the first place.
The issue will be whether the instrument you have has retained
all of its original magnetism
hairspring tension
mechanical tolerances.
The reason that there are very few references to instrument making on the net is that there are very few of us doing it professionally these days and there is a little more to it than there first appears.

The only internet resource I've ever found on the subject is the manual that Anthony Rhodes has written about Smiths and Jaeger speedos, available here:http://home.comcast.net/~rhodes/speedo.html. I'm pretty sure thats where I first learned about the 'dot'. I've cleaned and rebuilt a few speedos, but without access to replacement parts its hard to do much in the way of repairs to them. I must admit that I damaged the last one I pulled apart by being ham fisted with the springs. Thats when I realised that Australian Smiths speedos are quite different from UK ones inside.

Tim