Devlin.. At risk of being too simplistic and painting a very rosy picture, what you have there is the Lucas Magneto, a self contained reliable instrument for generating accurately timed high tension voltage (sparks). The advantage being no external electrical power source is necessary, as in the more modern systems of coil, points or electronic trigger types of ignition. Well they were 70 or more years ago when they were new. Time and tide wait for no man, and problems are to be expected.
That was then, and fortunately there are at least two well known Forum members who can turn the failings of this cursed device back closer to the reality of when they were new.
Standard magneto on that bike is a Lucas K2F. K for the model designation, 2 for the number of plugs, F for flange mounting. Old Joe Lucas was fairly logical. At the other end, with luck there is a stamped identity plate, next to this is the screw for the armature earth brush. It will say K2F AC then numbers like 7 48 and a final long number. K2F is straightforward, that's what it is. AC stands for anti-clockwise, the direction of rotation when viewed from the drive end. 7 48 given here as an example is the date code. July 1948. The final number is the build spec. Lucas units were used throughout the Brit Bike market, and an otherwise almost identical unit fitted to another model or manufacturers' range will have a different build spec. The differences may have been minor, but all variations required their own notation. A cross reference of this spec number on published Lucas Parts lists gives the part number identity of what's inside, from the major components down to the smallest clip, washer or screw. In practice if a magneto fits and works, that's good enough for the likes of me. Perfectionists go the extra mile in the search for correct for the year numbers.
Lucas were always Known as "The Prince of Darkness" for good reason. Wipac had a worse reputation, but in fact set up properly original Lucas stuff is pretty good. It was not designed with longevity in mind, but always down to a price. I'll wait for the laughter to subside, and meantime recommend Priory Magnetos and Brightspark Magnetos as invaluable resources of information and practical help.
That magneto has the bakelite points cover, screw in terminal goes to cut out switch as mentioned by Musky,(some come with a bell push button cut out) later models have a screw on cap again with wire to the cut out switch. A spring/weight controlled automatic advance unit at the drive end was the usual fitting on everyday bikes. More sporting variants have manual advance/retard, along with a fixed drive gear,
Swarfy.
