AJS & Matchless Owners Club

As I understand it, the early 60s SN speedo, or Nemag type, is distinct from the 1964-on SM magnetic type. Personally I refer to the SN as Chronometric for simplicity's sake and mainly to distinguish it from the later magnetic speedo. More importantly I think Gaggs are incorrect with reference to the cable type because it contradicts Smiths' own catalogues.

Smiths list the DF1110/22 cables for the Lightweight SN speedos, exactly the same as the Heavyweight Chronometrics apart from the length. When AMC switched to the true magnetic SSM2001 speedos for the Lightweights in 1964, they changed the cable type to DF9110/00, same as the Heavyweight magnetic cable. So I'm standing by the Chronometric/Magnetic speedo distinction for Lightweight cables.

Confusing i am keeping out of this one!

Ah, Ok I think the black ones are referred to as 'Chronometric' and the grey ones as magnetic, when in fact they are all technically magnetic but probably differ slightly in the cable attachment. Interesting. Possibly got the wrong cable then, oh bother...

The main issue with Chrono vs Magnetic cables is that the inner on a Magnetic is 1/8" longer (protruding 9/16" instead of 7/16"), so a Magnetic cable would cause damage to a Chronometric (or SN) speedo. To my knowledge the shorter inner means no damage would occur by accidentally fitting a Chrono cable to a Magnetic speedo.

The grey face issue is a potential red herring. Heavyweight Chronometric speedos had a grey face in the early 1960s, so people often mistakenly assume they're Magnetic speedos. The model reference on the face is the only reliable indicator - if it's got M in the code, then it's Magnetic.

Ok so the earlier cable will fit both, but the later cable will only fit the later instrument.

Not really - I don't think the lesser protrusion of a Chrono cable would be good in the long term for a Magnetic speedo but not as bad as vice versa. I think the simple rule should be Chrono cable for SN speedos and Magnetic for SSM.

Steven S wrote: ↑Thu Jun 24, 2021 11:02 am Not really - I don't think the lesser protrusion of a Chrono cable would be good in the long term for a Magnetic speedo but not as bad as vice versa. I think the simple rule should be Chrono cable for SN speedos and Magnetic for SSM.

You are correct Steven the shorter chronometric cable used on a later magnetic speedo (SSM lightweight and heavyweight) might work initially and would not cause immediate damage. However over time there is a risk that the shorter cable will wear causing damage to both the cable and drive in the speedo. The other way round, the magnetic cable used on a chronometric speedo (SN lightweight or SC heavyweight) will wear out the drive pretty quickly. Given the tendency for our bikes to acquire non standard parts over the last 50 or more years it is sensible, as Steven has said, to work on the number on the face which may mean you need a different cable rather than the correct cable for the bike.