|The mainshaft low gear has not changed much since 1952. The factory did change to a dash-A suffix, which will retrofit to the earlier part without a suffix.
The early parts book list both gears as 29 teeth. This is likely a typo.
|The Iron Sportster mainshaft is a triumph of engineering. The general design has sustained from 1952 to 1984. There were teething problems in the early K-model, but they were all cured by 1957 with the introduction of the Sportster.
Mainshaft low gear is in the darker oval. Gears are named for carrying power, not the order on the shaft. The gears from left to right are mainshaft low, mainshaft 3rd, mainshaft 2nd, and the clutch gear.