|The mainshaft 3rd gear has not changed much since 1956. The factory did change the number of teeth on the earliest gear, from 21 to 20 in K-models and Iron Sportsters from 1954 to 1984.
||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 second 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.