Technical Q and A for classic motorcycle maintenance and repair.
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 your subject.
Triumph T100SS and an Energy Transfer System
Q: I am now in the process of rebuilding my first bike. My 1963 Triumph T100SS Scrambler has no battery, as it runs on the energy transfer system. It hasn’t been on the road since 1986, when it got a pencil-sized hole in the right piston. All the books, maintenance manuals and online materials are too general, showing illustrations that do not match my engine or directing me to steps that do not apply to my particular bike. Have I just not been fortunate enough to find a truly appropriate manual, or were too many of the specifics of different models lost over time so that now all materials are just too generic? My engine number is H30587 and is stamped a T100SS. Can you direct me to any materials or sources of info you may have pertaining to these energy-transfer machines. — Kevin Gennario/via email
A: It took me the longest time to really understand the ETC system; it’s so different from a standard battery/coil ignition. In fact, it’s closer to a CDI-type ignition than battery/coil. The biggest difference between the ETC system and battery/coil is the way the coils are charged and discharged. In a battery/coil system the alternator’s output is rectified from AC to DC and smoothed out to provide a steady level of voltage to charge and discharge the coils. In the ETC system the ignition voltage is taken directly from the alternator. Since the alternator is supplying the voltage directly, and it is alternating current, you have rising and falling voltage as the rotor spins inside the alternator coil. You want to fire the coils as the alternator is generating peak voltage. In a normal battery/coil ignition the points are in series with the primary side of the coil. Voltage charges the coil, then the points open, interrupting the primary coil circuit. The magnetic field collapses, inducing high voltage in the secondary windings, which is discharged through the spark plug. In the ETC system, the points are in parallel with the coils. The primary side of the coil is kept grounded until the alternator reaches peak voltage, then the points open, allowing the voltage to flow through the primary side of the coils. The surge of current induces high voltage in the secondary windings of the coil, which is discharged through the spark plug. Because you are taking the output of the alternator directly you want to time the peak alternator output to the instant of the points opening. This gives you a very narrow range of ignition advance and is why the points plate on an ETC system only allows a 5 degree advance. Just a few degrees one way or the other can really keep the bike from running well. The back of the ETC alternator rotor has three holes that can be engaged by the matching pin on the crankshaft. They are marked S, M or R. For most street use you will want to use the S setting, which puts the maximum advance at 37 degrees BTDC. The M and R settings are for racing and can make the bike difficult to start because they preset the advance higher than normal. This Triumph Service bulletin explains it all. MC