Classic BMW Resources
A list of suppliers and resources for classic BMW motorcycles
May/June 2007
By Bill Stermer
A word on magneto ignitions
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BMW enthusiast Darryl Richman notes that most pre-1970 BMWs have magneto ignition, “which is a mysterious device that produces sparks out of nothing. Magneto bikes don’t need a battery, nor do they need a functioning generator. Magnetos are also extremely reliable and can be very long lived. They have two downsides, however. One is that because they produce more power the faster they spin, their output is fairly weak at kick-starting speeds — when you really want the strongest spark. This means that a machine has to be in pretty good tune to kick it to life. The other is that the mag coil is a very specialized device that has thousands of windings in a particular pattern. The old, very fine wire was insulated with a kind of shellac that can break down over the decades and can short out, effectively cutting down the number of windings and the power produced. Or the wire itself can break from vibration.
“The classic symptoms of a magneto going out are that the bike starts when cold and runs, but won’t restart when hot. If you wait 30 minutes to an hour, the bike will often start again. Eventually, the time interval before it will start once again increases. What’s happening is that the shellac is migrating out, but the wires don’t actually make contact with each other until they expand from heat. While the bike is running there are still enough effective windings to keep sparking, but not enough at kickstart speeds.”
BMW Books
Richman recommends obtaining copies of the parts and owners manuals, and a shop manual, when available. The parts books make ordering parts from vendors a lot easier. “There’s a Clymer manual for BMW bikes 1955-69, which is quite helpful. In general terms, however, there are three books, all now sadly out of print, but that show up on eBay and at used book stores (try http://www.half.com, for example) that can be really helpful in choosing a bike and determining completeness and correctness.”
The books Richman alludes to include Bahnstormer, The Story of BMW Motorcycles, by L. J. K. Setright, How to Restore Your BMW Motorcycle - Twins 1950-1969, by Roland Slabon (be careful when searching for this book: Motorbooks has issued a new edition by a different author which appears to be a step backwards) and the Illustrated BMW Motorcycle Buyer’s Guide, 2nd Edition, by Roland Slabon and Stefan Knittel.
BMW Motorcycles (ISBN-13: 978-1-884313-57-8, Whitehorse Press), by Kevin Ash
Just released by Whitehorse Press, this book carries a brief compendium of BMW motorcycles from the very beginning to the new F800 twins. Consider it the latest means of keeping all the models straight.
www.whitehorsepress.com
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