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Misc: Speedometers Smiths Chronometric Speedometer

tractorman414

Well Known and Active Forum Website User
VOC Member
I have a 3" Smith chronometric speedo with a rather poor condition dial and by a stroke of luck I happen to have a brand new replacement dial, however only one of the 4 fixing screws is present, and I am struggling to identify what the screws are, they measure 0.077" OD and are 56 tpi of near abouts which doesn’t relate to any thread standard I know, and ideas what they are and more importantly, where can I get some ?
 

clevtrev

Well Known and Active Forum Website User
VOC Member
I have a 3" Smith chronometric speedo with a rather poor condition dial and by a stroke of luck I happen to have a brand new replacement dial, however only one of the 4 fixing screws is present, and I am struggling to identify what the screws are, they measure 0.077" OD and are 56 tpi of near abouts which doesn’t relate to any thread standard I know, and ideas what they are and more importantly, where can I get some ?
The thread is M2 x .45 pitch.
 

tractorman414

Well Known and Active Forum Website User
VOC Member
Many thank Trevor, but horror horror, metric threads on my Vincent.

I did run through the metric thread tables, but could only find M2 listed at 0.4 mm pitch [approx 64 tpi] and only M2.5 listed at 0.45 mm pitch [approx 56 tpi] So M2 at 0.45 mm pitch must by an old discontinued standard ?

Expect I will end up drilling and tapping to an available screw.

Bernard
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Website Moderator
The Smiths chronometric speedo was originally a French design under the Jaeger name and is a completely metric design using metric threads. Even though it is called a 3" speedo, it actually measures 80mm in diameter and even the 2 mounting studs on the back of the 3" casing are M6 and not 1/4 BSF. The name chronometric gives it away. The only imperial part is the calibration for miles and MPH.

Cheers,
Simon.
 

john998

Well Known and Active Forum Website User
VOC Member
Speedo

Wish this had appeared earlier, Just changed the guts of a 5" clock that had a worn out mileometer. The 3" spare donor item only had 2 tapped holes for the dial mount. I cheated and tapped the holes the nearest BA size. Having said that the chances of getting the correct screws do not look good.
Not wishing to be picky but my 3" speedo only has 2 screws fixing the dial. John.
 

nkt267

Well Known and Active Forum Website User
VOC Member
Some have 2 screws and some have 4. 1 Comet in the garage has 4 the other has 2. I have 2 identical 467's in the cupboard 1 has 2 screws the other has 4.I'm sure someone out there has some logic for this as just age cannot be the reason as my '32 Sunbeam has 2 screws for the dial:confused:..John
 

tractorman414

Well Known and Active Forum Website User
VOC Member
Wish this had appeared earlier, Just changed the guts of a 5" clock that had a worn out mileometer. The 3" spare donor item only had 2 tapped holes for the dial mount. I cheated and tapped the holes the nearest BA size. Having said that the chances of getting the correct screws do not look good.
Not wishing to be picky but my 3" speedo only has 2 screws fixing the dial. John.

Thanks John, having stripped this unit I decided to "do up" a couple of others, and note that some have 2 screw dial fixing and others 4 screw. I also mistook the mounting studs as 0 BA ! Great fun straightening a needle with a 120 degree bend and twisted to boot !

Can you tell me about what appears to be dating code on the casing. Stamped on the back is what resembles a dart board grid with 12 radial divisions and divided to form 2 rings of segments. If you look carefully, you may have to clean the paint away, but there are 2 centre punch marks, one in the inner ring and one in the outer. On all the speedometers I am working on the marks are in different segments. So looks like a date code.
 

john998

Well Known and Active Forum Website User
VOC Member
Speedo

Well observed, I had seen that symbol but assumed it was just a trade mark.
Checked all 3" cases to hand, but only one obvious punch mark between them.
I think you are right, it may be a dating system, although it is hard to see how without a year mark. Regards John.
 

clevtrev

Well Known and Active Forum Website User
VOC Member
These sizes are still fooling KTB, now in it`s fourth issue. Still tells you the fixings are 0BA , and the cable nut at the speedo end is some obscure CEI size, rather than the M12 x 1mm pitch that it is. Obviously no one has ever measured the threads, just taken a casual guess.
Perhaps I should also mention the Burman box, and the long studs, that go through the two outer covers. They are not 5/16 studs with a Whit thead ate one end and a BSF thread at the other, the body of the stud is 21/64"dia and it`s actually a dowel.
I think the dating system just shows year and month, I will ask an old Smiths man, and try to find out.
 

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