Intended as a direct replacement oil pump, S&S billet oil pumps, incorporate some unique S&S design features. Installations on engines from 1936-'69 can be a simple bolt-on, or the oiling system can be updated with simple drilling steps with the S&S drilling fixture. Engines from 1970-'72 require a drilling step and a plugging step. Engines from 1973-'80 require only the drilling step. Both steps can be performed while the engine is in its chassis. Installations on 1981-'99 engines are strictly bolt-on and require no crankcase modifications. Easy to follow installation instructions are provided with every kit. Features and Benefits: Same width oil supply and return gears as the stock HD aluminum pump. S&S pinion and oil pump drive shaft drive gears increase potential oil volume delivery by 25% over stock on 1972 and earlier engines. S&S pumps for 1936-'67 engines used with the S&S oil pump drive gears deliver 33% more oil than the original cast iron pump. Machined with an oil pressure relief bleed off passageway-relieves pressure build up on top of the valve to maintain consistent oil pressure. Oil pressure regulation bypass routes excess oil directly to the supply side of the pump. reduces the amount of oil returned to the tank, less foaming and cavitation. The standard pump cover allows total flexibility for oil system configuration with a number of oil feed and return options.