I am trying to get to the bottom of this subject, and have found a really excellent section in the ‘Radco’ book “The Vintage Motorcyclist’s Workshop” (highly recommended, and recently reprinted, so easily available again. They were fetching £200 a copy on eBay until about three months ago !). Pages 158 and 159 chart the differences between K and M type magnetos, and also compare them with the German standards. For instance a British A2 magneto should have similar dimensions to a German ZA2, and as I stated, anything with a V in it’s type number was indeed originally a V-twin magneto. On page 160 it also confirms,and I quote, “During the last war BTH turned out some very nice single and twin-cylinder stationary engine magnetos with fixed ignition. These crop up brand new from time to time. The lack of advance-and-retard facilities can be overcome by fitting a vintage BTH contact breaker housing, which will usually go straight on without further modification”.
What we are faced with 70 to 80 plus years later can easily be a mongrel, that has been modified any number of times in desperate attempts to keep a bike going during the long years before our vintage machines began to be appreciated, and specialist magneto repairers began to reappear. I am so glad that my previous comments have been affirmed by a real expert, the late Frank Farrington.
Brian
