Robert Allen wrote:
> For those still following this, I cannot find any adjustment for either
> the spring or the magnetized disk. I am just curious which is changed to
> effect calibration: the tension in the spring or the degree of magnetism
> in the spinning disk.
This is what I remember from a speedo article or manual I read a while
ago. Of coure I can't find it, but this is how I think you adjust it.
Or, in other words, I'm no expert, use at your own risk.
Usually (I can't speak for Smiths specifically though) you calibrate
by moving the magnet closer or further away from the 'pan'. This can
be acomplished two ways, either moving it 'inward' towords the pan (still
centered) or sideways (off center) so the edge of the magnet disk is
closer to one side of the pan lip.
Either way the closer the magnet is to the pan, the more magnetic
influence it has, therefore the higher the indicated speed. Conversely,
the farther away, the slower the speedo.
Look for some fine threads somewhere for adjustment. Usually there is
some access hole or screw to adjust the speedo externally, but I suppose
with the obfuscated British mechanical philosophy you might have to
actually bend or replace something.
As far as changing the spring goes, it does seem that the weaker the
spring the higher the speedo would read, so I suppose you could adjust
or replace accordingly. But, I've never replaced a spring, so I'm
unsure how 'do it yourself' it is. Seems a little too delicate though...
I've looked in a few of my repair books, and none of them seem to be
of any help. Even the German manuals (where there's a measurement for
everything and a unique tool too) are silent on the subject.
"always in a automotive frenzy"
P.S. It might have been a motorcycle manual.....
I will keep researching, if no one posts a definitive answer.