In defence of ET systems

In the December 2020 issue, Tim Britton asked to hear from people who have had good experiences with Energy Transfer (ET) ignition systems. I’m such a person, quite pleased with the ET systems on two of my bikes that I’ve ridden for decades (20 and 50 years).

Although it’s popular to criticize the ET system, my experience is that most such criticism is undeserved. That said, it is more sensitive to sloppy maintenance than a ‘regular’ ignition system, and it only produces 35 Watts for the headlamp. On the other hand, an ET system completely eliminates the need for a battery, along with the cost and maintenance issues that go with it.

Just prior to the Second World War Bendix introduced a ‘low tension’ magneto that placed the high-tension coils adjacent to the spark plugs, eliminating high altitude arcing problem. This magneto was used on all Double Wasp radial engines during the Second World War (Corsair, Thunderbolt, Hellcat, B-26, etc.), proving the intrinsic reliability of the design. The Bendix low tension magneto is electrically identical to the ET system, which also was used to good effect on various off-road Hondas and Yamahas during the 1970s.

What ended the use of the ET system by Triumph and BSA, at least for street bikes, was a 1967 US law that required tail-lights on new machines to remain on when the engine wasn’t running. However, the ET system remained in use by BSA for offroad machines until the end, including on their premiere (and last) 1971 B50MX.

Unfortunately, a half-century later an intrinsic manufacturing defect of ET coils has reared its head, causing some or all of them to die of old age, even when not used. My speculation is the factory used slightly acidic flux to solder the very fine wire of the secondary (0.003in dia.) and that this slowly corrodes the wire with time. Luckily, suitable replacements are now available. Charles Falco, California, via email.