-SG- These magnetos seem to have been used considerably - from before WW1 through to at least the mid twenties, although not on all models: many of the side-valve engined machines from about 1922 onward being fitted with ML instruments. At this distance it is only supposition but the reason for Norton going the CAV way may well have been a result of the take-over by Shelleys - and who owned Shelleys? - C A Vandervell. I have never used a CAV magneto myself and they may well be excellent but the magneto repair man I use declines to accept work on them, using one short four letter word to describe them! CAV's 1922 folder is attached via this link.
Roger recalls that the twenties Brooklands Nortons were fitted mainly with CAV magnetos but the repeated magneto problems during the '100 in the Hour' efforts (June 1927) at Montlhery meant a change to a Bosch for the actual record. He goes on to say that the main problem with the CAV design is the fibre wheel in the contact breaker which distorts, making it impossible to set the points gap correctly. Tufnol versions have been tried with no noticeable improvement so if anyone has come across this problem before and has a good solution for it, it would be good to have details.