Norton singles clutch spring dimensions

Here's a triplet of New Year teasers for the combined brains of the Norton Owners Club. Nobody I have asked so far can give me chapter and verse on this, so here goes:-

I have a couple of standard 3-spring clutches that I am putting together from a pile of bits. The parts list shows the clutch spring box [Part No. A2/400] for Models 1, 16H, 18, ES2, 30 and 40. As is usually the case, there is a similar but presumably slightly different item for the 30M and 40M [Part No. A11M/400].

The clutch spring boxes I have are the same diameters, but some are 40mm and others are 36mm long.

• Is one of these A2/400 and the other A11M/400?
• Does the shorter one go with a 30M or 40M clutch that has a total of 7 plates against the total of 10 for the rest of the bikes?
• Is the shorter one used to produce a stronger clutch pressure by compressing the spring more?
• Am I looking at two sets of clutch spring boxes from a number of years apart?

It gets worse. There is more than one version of the clutch springs:-

• Set 1 - Uncompressed length 45.5mm; cross section 2.65mm
• Set 2 - Uncompressed length 44.2mm; cross section 3.00mm
• Set 3 - Uncompressed length 42.3mm; cross section rectangular 2.6mm x 2.5mm

Am I simply seeing a variation in length due to use or a different manufacturing spec? Were there different spring lengths and sections for different models at different times? The parts list indicates Part No. A2/399 for all the road Models but I seem to remember somebody telling me that the Manx ones [Part No. A11M/399] are the square springs. Is this true?

Lastly, there are two thicknesses of clutch back plate. I have one at 2.3mm and a thicker one at 2.9mm. Can anyone shed any light on why there is this difference and what Models these might fit?

At the end of all this, it is not too much trouble to set things up with the various parts and see how it all behaves, but it would be interesting to know what this all means.