This guide will show you how to change the oil in the transmission of the Evolution motor of the Harley-Davidson Sportster. [ … ] The Evolution Sportsters have wet clutch and primary drives. It is recommended to change the oil at 1,000 miles, then every 10,000 miles after that. [ … ] The manufacturer recommends using 20w50 oil. Make sure that the oil you use is approved for wet clutches. Many automotive oils are not, so we recommend purchasing an oil that specifically states it's formulated for use in motorcycle transmissions. 75w90 gear oil is often substituted for 20w50 motor oil in this application.