Reckon Flashback's theory is the most-often-stated one . . . but how many manual mags used fibre-drive? Haven't met a plastic sprocket or chain yet. So the built-in 'first point of failure' argument does not work for me. And yet, so many manufacturers went with the fibre option for twins. BSA, Triumph, Velocette, Vincent even. I have no real idea why. Norton twins managed with chains and steel like any good sado-masochist, so did Royal Enfield, AMC ran steel pinions on twins. Nobody apparently told them they shouldn't. Fibre's quieter, almost for sure, but that's about it. And when there are up to six pinions in the train for any bog standard twin camshaft motor, what's the difference in practical terms? Maybe it was Mr Lucas who proposed it, as I imagine he sent the ATDs ready assembled to the factories. All I can say is I wish he hadn't.
And another thing - Magdyno pinions for the dynamo . . . yuk.
