Harley Davidson oil pumps are two-sided, gear-type, positive-displacement pumps. The oil pump drive shaft is driven by the cam gear-train which passes through the case and into the back of the oil pump body. Two sets of gears are keyed to the drive shaft: a thick set and a thin set. The thin set supplies high-volume, low-pressure oil to the engine’s oil system. The thick set, or return set, draws oil that is collected by the breather valve and forces it through the oil filter and back into the oil tank.
Installing Harley Oil Pumps
1. Locate the drive key slot in the drive shaft close to where it exits the case. Insert a key into the slot and insure that it nests fully in the groove evenly without cocking. Slide the thin drive gear onto this shaft and engage the drive gear key into its slot on the gear.
2. Place the thin driven gear onto its mounting stud on the backside of the pump body and hold it in place. Place the new inner pump gasket onto the locating studs on the case and slide the pump body onto the drive shaft. Rotate the driven gear until the drive and driven gears nest together, allowing the pump body to slide up tightly against the case.
3. Insert a key into the drive shaft where it exits the front of the pump body. Slide the thick drive gear onto the shaft and engage the drive gear key onto its slot on the gear. Slide the thick driven gear onto its mounting stud and rotate the gear until it nests with the thick drive gear.
4. Place the pump cover gasket onto the locating studs. Slide the pump cover onto the locating studs and install the cover bolts finger-tight. Tighten the cover bolts to factory spec and in the approved pattern set by the manufacturer. Install the oil return line onto the spigot on top of the pump and install a new clamp with the factory crimping tool.