If you don’t change your Harley-Davidson bike’s primary oil on time, it caned up, damaging your bike. Fresh primary oil will lubricate the transmission and clutch. If you allow the oil to get too old, it can start breaking down and form sludge. It could clog up the transmission and create problems with shifting gears. Moreover, it can lead to premature wear on the clutch plates. In other words, you must change the primary oil on your Harley-Davidson bike on time if you want smooth performance.