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18S speedometer #771382 04/18/19 1:10 pm
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klektermaniac Offline OP
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Hello All,

I have a 1954 AJS Model 18S and now I am up and running I have discovered a new problem.
When travelling at approx. 30-35 mph, the speedo is showing around 80 mph. Where do I look for answers? I have had the rear wheel off (which includes the speedo drive gearbox) and speedo cable detached, but that is all.
The speedo is a Smiths chronometric 120 MPH with the numbers 5C 6301/45 1050.
RogerH.

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Re: 18S speedometer [Re: klektermaniac] #771457 04/19/19 3:35 am
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Rohan Online Content
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The speedo drive unit on the rear wheel is the 1st place I'd be looking.
A chronometric mph speedo requires a 2:1 ratio.

Pretty much all later speedos use something that spins the cable slower/faster.
I'd guess you have something later.

I don't recognise that speedo number at all in respect of chronometric speedos.
Smiths had a convoluted system of numbering, which takes some deciphering.
However, that 1050 in the speedo number could mean its something quite unusual,
Its related to rpms, and I can't readily find any reference to it.
Could it be km/hr, with a mph face ???
The parts list for my Ajay lists all the chrono speedos that could have been fitted from new that year,
do you have similar ?

So, what is written on your speedo drive unit ?

Re: 18S speedometer [Re: klektermaniac] #771506 04/19/19 5:03 pm
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Gordo in Comox Offline
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I would think that the issue is with the actual speedo and not the drive unit. The drive unit ratios did not vary enough to cause a 130% display error.

Gordo


The roadside repairs make for the best post ride stories.
Re: 18S speedometer [Re: klektermaniac] #771561 04/19/19 11:35 pm
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Rohan Online Content
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Lets start with the basics.
That 2:1 drive is about mandatory with chrono speedos.

I did mention that number quoted on the speedo is odd though, that doesn't come up
anywhere in connection with chronometric speedos. ?
And that 1050 rpm per mile ? (per km ?) is somewhat out of the usual ?

Re: 18S speedometer [Re: klektermaniac] #771584 04/20/19 3:34 am
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Bodie Offline
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I'm no expert on AJ's or what speedometer ? - But just out of curiosity I did do a quick search on your question & it looks like your bike should have an 80mph speedo fitted not the 120mph as per info from AJS & Matchless owners club ~> http://inetc976.inetc.net/forum/viewtopic.php?f=18&t=22364&start=10

It "Might" be just as simple as swapping out the 120mph face for an 80mph face or maybe easier if one of these are correct for your bike ? .https://www.eBay.co.uk/itm/293056485776?ul_noapp=true …. https://www.eBay.co.uk/itm/233197577561?ul_noapp=true

Re: 18S speedometer [Re: klektermaniac] #771587 04/20/19 4:56 am
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Rohan Online Content
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I too think it may be a dial face issue, possibly coupled with a speedo drive mismatch ?

The parts book for my 49 Ajay lists both 80mph and 120 mph chronometrics, as well as km/hr equivalants.
In later years there were also illuminated and non-illuminated, as well as trip and non-trip versions.
I think that gives at least 16 different varieties ?

And, I rather suspect this may be a magnetic rather than a chronometric ?
That number doesn't seem to connect with the known usual chronometrics.
And Indian sourced ones can say anything on the face, even if they are mostly all magnetic.
There are also car type ones, which are not so dissimilar and another kettle of fish.

Re: 18S speedometer [Re: klektermaniac] #771655 04/20/19 11:28 pm
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Rickman Offline
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I think I am going to suggest that the first two digits, instead of being 5C, should be SC?

Please take a closer look under brighter light and maybe a magnafying lens, and make certain sure of what is being read? And really clean the glass face, or twist off the threaded bezel to get a clearer look, if possible?

I may be wrong, as I certainly have never seen every chrono speedo ever produced, but even my late production grey faced chrono speedo for my '62-'63 A-65's is prefaced with that "SC" numbering...

Re: 18S speedometer [Re: klektermaniac] #771657 04/20/19 11:55 pm
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Rohan Online Content
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Thats a good suggestion.

Also examine the other numbers carefully, as even searching without a prefix I didn't find any 6 type speedos.
Which is not to say they would all have made it online - and they are not in the Smiths docs I have sighted.

P.S. In fact, SC 5301/xx seems to be a very widely used series of speedos.
xx seems to occur as quite a range of numbers, as does the rpm figure.

Re: 18S speedometer [Re: klektermaniac] #771862 04/23/19 3:47 pm
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klektermaniac Offline OP
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Hello All,
Thanks for the replies but the Good Lady told me to have some "Family Time" over Easter, hence no shed time!

First Rickman is correct in that the first two digits should read SC and not 5C - they are right under the needle and difficult to read. Also I have had a senior moment and the correct speedometer number is 5301/45, space, then the 1050.
The drive on the rear wheel is a Smiths 2 to1 ratio - British Patent 529397. Are the Smiths drives normally reliable or can they play up?

I bought this bike off a mate some 3 1/2 years ago, hence the recommissioning, and although he only rode it a couple of times he seems to remember the speedo working OK at the time. He is mechanically challenged but even he would notice that, and if it needed any work he always took it to a garage to be fixed, so he would not have been fiddling with something he did not understand. However this bike is a bit messy, having a 350 clutch, and a Q/D rear wheel which I did not think were fitted to a '54 model.

I do also have a Matchless G3 with a 120 MPH speedo fitted (optimistic?) and on that one the 0 to 120 go from 1 o'clock to 11 o'clock, but on this AJS 18S they go from 7 o'clock to 5 o'clock, which probably means nothing.

RogerH.

Re: 18S speedometer [Re: klektermaniac] #771877 04/23/19 9:36 pm
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Rohan Online Content
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Well that solved the numbers quandry easily enough.
That 1050 bit is still a bit of a mystery though, most of the SC 5301 speedo types
about seem to have numbers more like 1600 or 1620 etc, which refers to revs per mile,
so maybe your particular one is for something a bit unusual - don't some later bikes
have a speedo driven out of the gearbox, no idea what sort of ratios they use.

Drives can play up - as the teeth wear they can skip, but tend to read less, not lots more.

Just a thought - could you try the G3 speedo on this bike.
And does its speedo have the rpm number printed on the face ?

If this proves successful, a good speedo shop could likely delve into the internals of your errant speedo,
and change the gearing inside - apparently Smiths were made as one size fits all, you 'just' need all the suitable bits.
No idea what this might cost though...

A lot of makers offered the 120mph as an alternative to the 80 mph one, inc AMC,
maybe it made the owners feel faster ?


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