Understanding And Maintaining The BMW /2 Electrical System

Short Description
This manual was written to help owners of /2 BMW motorcycles to service their bikes and keep them in running condition. When these motorcycles were made, they had very different electrical requirements to motorcycles today, and used equipment which today’s owner may not fully understand. Doug and Kees hope that this manual is useful to owners of these motorcycles and that it will help owners keep their bikes where they belong - on the road.

Website: www.snafu.org | Filesize: 3245kb
No of Page(s): 28

Content
The BMW /2 motorcycles have what could be viewed as two electrical systems - one for the engine (ignition), and one for all the extras such as lights and the horn. The ignition system consists of the magneto, coil, points and the sparkplugs. The ancillary system includes all the bulbs, the battery, generator, horn, and switchgear. Because of this separation, it is possible for the engine to run quite happily despite major faults in the rest of the wiring system. Early electrical components weren’t very reliable, and this was a major reason why many vehicles, and motorcycles in particular, had this kind of separation. However, after the Second World War, other vehicle manufacturers started moving towards the coil system of ignition, and integrating the electrical systems together. BMW remained with the split electrical system for some years, only changing to coil ignition and a single electrical system when the /5 motorcycles were released in 1970.
…
At a very simplistic level, your /2 ignition works similarly to ignition systems today.
1. A charge is built up;
2. This is released as a voltage spike when the ignition points are opened by a cam on the end of the camshaft;
3. This spike passes through a coil which transforms it to an extremely high enough voltage;
4. This jumps the gap at the end of the spark plug, and thus ignites the fuel in the cylinder.
That was the simple version. The truth is somewhat more complex.
…