Harley Davidson built the Panhead engine from 1948-1965.These engines were called panheads because of the rocker covers which look like upside down roasting pans.The biggest improvement on these engines was the addition of hydraulic lifters.By using hydraulic lifters it cut down on valve train noise and made maintenance eaiser as hydraulic lifters are self adjusting and do not require periodic adjustment like solid lifters.Another improvment occured during 1952. When Harley introduced the hand clutch footshift.This did not catch on rite away almost half a decade after being introduced most riders made the switch.