Motorcycle Classics Blogs > Tech Corner

Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.


BSA C15S Energy Transfer System Conversion

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Energy transfer conversion

Q: I would like to convert my BSA C15S with the energy transfer system to a 12-volt battery/coil system, but I have no idea how to accomplish the task. Can you help me? — Bruce Riecke/via email

A: To begin, you will need a 12-volt stator. It also wouldn’t hurt to buy a new rotor, as they lose magnetism over time and won’t create as much current. You’ll also need to replace every bulb on your bike with a 12-volt equivalent. You’ll need to replace the energy transfer (ET) coils with conventional 12-volt units. If your ET coils are original equipment and in good shape, keep them someplace safe, as they are worth their weight in gold. You will need a 12-volt battery and a 12-volt rectifier, or you can use a Boyer Powerbox and continue to run without a battery. You will also need to find a 12-degree auto advance unit to replace the 6-degree ET unit. When I got my 1964 Triumph T100SC with ET ignition years ago, I wanted to upgrade to a 12-volt battery/coil but was advised against it by an old flat track racer who lives in my area. His advice was classic. “Does it work now,” he asked? “Yes,” I replied. “Then don’t mess with it.” I’m still running my ET. MC