speedometer type

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chris.matthews
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speedometer type

Postby chris.matthews » Sat May 04, 2019 1:24 am

Greetings from springtime Japan.
My 1939 VB has speedo in the tank panel. Its a Smiths PA.
My 1948 All Iron 4G also has a speedo in the tank panel. Its a Smiths Chronometric.
I wonder if the 4G should be PA - I hope not due to hens teeth & cost.
When did the changeover occur ?

Interestingly, my 1938 Velocette has a Smiths Chronometric - I believe it to be correct as I have never heard reference to PA on the Velo Forum.

Best regards,
Chris Matthews

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Re: speedometer type

Postby Dave.Barkshire » Sat May 04, 2019 9:49 am

Hi Chris

So far as I know the chronometric is correct for post war Ariels.

My 39 Velo MAC had a chronometric and they are correct for pre war Velos.
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chris.shearwood
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Re: speedometer type

Postby chris.shearwood » Sat May 04, 2019 1:17 pm

Hi Chris,
According to Roy Bacon's book, 1948 was the year all Ariels went chronometric. My 46 Sq4 has a PA.
Regards, Chris
1946 4G, 1950 NG and 1951 VH

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Re: speedometer type

Postby Brian Petheram » Sat May 04, 2019 5:23 pm

According to the 1939 catalogue a fork mounted front wheel driven speedo was optional for the VB - presumably a Chronometric.

I'm very aware of this because my 1939 VH needs a speedo. It left the factory without one, presumably because it was originally exported to Denmark, but I need one to be road legal in the UK. The PA speedo situation seems rather challenging to say the least - if anyone has one please PM me, I have swaps and cash! I expect I'll end up with a blanking plate in the panel although a chronometric with a right angle drive would fill the hole.

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simon.holyfield
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Re: speedometer type

Postby simon.holyfield » Sat May 04, 2019 5:52 pm

Curious that the PA and the Chronometric were being sold at the same time - but then I guess chronometrics & magnetic speedos were sold by Smiths at the same time too.

Is the performance of a PA similar to that of a chronometric? Were they significantly cheaper than one another?
cheers

Simes

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Re: speedometer type

Postby paul.jameson » Sat May 04, 2019 6:59 pm

The Chronometric speedo, as the name implies, works in a manner similar to that of a clock. As a result, it is highly accurate, provided of course that the gearing to drive it is correct. On Ariels, it uses a flex speed (speedo cable rotation at 60mph) of 1610.

The PA speedo works on the governor principle but can be surprisingly accurate. It relies upon a small coil spring to determine the movement of the pointer and these springs vary depending whether the speedo was originally 60, 80 or 100mph. Most 60mph PAs went into cars and had a flex speed of 3360. The Ariel ones had a flex speed of 2240. Logical really, given that in the 1930s a car's cruising speed might be 40mph whilst a bike could do 60mph easily enough.

I have a number of PA kits available now and I hope to be able to bring some for sale to the Annual Rally in Pershore, providing that I can get them put together by then.
Paul Jameson
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Re: speedometer type

Postby john.whiting » Mon May 06, 2019 12:02 pm

Would not a prewar chronometric speedo be a British Jaeger?

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Re: speedometer type

Postby TonyBaxter » Fri May 10, 2019 8:21 am

Is there an angled drive that fits the back of a chronometric, or is it a special chrono that has the drive exiting at an angle?

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Re: speedometer type

Postby andyhughesflattankarielpre25 » Fri May 10, 2019 10:04 am

There was an angle drive adaptor used by Vincent for the big clocks they used,this was also used on ford d series and jags, and probably others as well,they had a wheel that you turned to screw them on the back of the clocks and the cable then fitted on ok.

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Re: speedometer type

Postby john.mitchell » Sat May 11, 2019 10:35 am

Is this what you are talking about? I would be interested to discover what this was used on.
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