How Does A Motorcycle Oil Pump Work?

Myron Hill invented the gerotor pump in the early 20th century

This is the oil pump from a Honda CBR600RR. It sits under the engine with its foot down in the oil sump. A lot of people call this a "gear-rotor" pump, but the inventor tells us it is a generated-rotor pump. His acronym is "gerotor." Generated means they created one of the two parts this pump consists of and then it generated the shape for the complementary part.

If we take off the housing, we see a four-lobe inner rotor and a five-lobe outer rotor. A gerotor pump has end lobes on an interior rotor and end plus one on the exterior rotor. As I turn this, you can see this space here is getting bigger. Now it’s become as big as it can. And now it’s starting to get smaller again.

The housing has an intake side and an exhaust side. The intake goes to the side of the rotor where the space is getting bigger so it draws in oil. And then it moves to the other side, where this space is getting smaller. That’s the deliver side of the pump. It sends that oil out to the oil system, first to the filter, then the main oil gallery, and onward to its many duties. Lovely…