Ignition Systems 1970-1978

Disconnector contacts in the camshaft cover.

A breaker cam that sits on the camshaft eliminates at least the gear pair that drives the distributor shaft. Any gear pair inevitably introduces backlash. Thus, in the precise control of an ignition timing, backlash is not welcome. Therefore, in 1970 on the Big Twin series and 1971 on the Sportsters, the breaker base plates were integrated into the camshaft covers and the centrifugal adjusters were placed on the camshaft. Fun fact on the side: on the 1929-1936 side valve models, the breakers were also already controlled directly by the rear exhaust camshaft. Only that at that time, they still controlled the ignition timing from the left end of the handlebar and not by centrifugal advance.

The individual components were the same for Sportster and Big Twins, only that the alignment of the cams and the breaker contacts were offset by 90 degrees.

Spare parts

Parts for these ignition systems are available from W&W either as a complete set or, as has always been the case with Harley-Davidson, as individual parts. When selecting parts, please refer to the year of manufacture and model number given with the parts or to the OEM number you have found in a spare parts manual. ACCEL offers a worry-free parts kit that's also great for your saddlebag - just in case.

How do I adjust the ignition?

The gap for the breaker contacts is 0.20 - 0.22" (0.5 - 0.55 mm). The ignition timing is set to the mark on the crankshaft with the engine stopped and the centrifugal weights disengaged. It is best to use a test lamp for this purpose. It is connected to the ignition coil at the same terminal as the cable to the breaker contact. The tip then to ground (engine case, etc.). When the breaker contacts open, the lamp lights up. This is your ignition timing.