John,
With the speedometer action you describe it would appear that the
mechanism inside is clockwork. This type of speedo is termed
"chronometric", I believe. In my '36 Series I, Chassis Number 121,
the speedo is of the magnet-driven type and was made by S. Smith and
Sons(M.A) Ltd, London. It has the numbers 34276/1 over 1600 under the
needle pivot.
Best regards,
Tony Souza
Ottsville, PA USA
----- Original Message -----
From: John Mott <johnmott@iinet.net.au>
To: <MSCCDG@yahoogroups.com>; <morgans@autox.team.net>
Sent: Friday, August 17, 2001 3:35 AM
Subject: SPEEDOMETER MECHANICS
> A friend of mine is restoring a 1936 Series 1 Coventry Climax 4/4
> When he tested the speedometer by rotating it with an electric
drill, he
> found that the speed registered jumped up in increments of about 5
mile per
> hour instead of the needle moving smoothly. Likewise it comes down
in
> increments rather than smoothly when the speed is decreased.
> An instrument maker suggested to him that this old speedo is
activated by a
> clockwork mechanism and that this incremental motion is normal.
> My only experience is of speedo's driven by a magnet in a drum, and
these
> move the needle smoothly.
> Can anyone tell us whether this incremental motion is normal, and
perhaps
> explain how these old speedo,s work?
>
> John Mott
> 1981 4/4 4 seater
> Western Australia
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