Balance shaft

Balance shafts are used in piston engines to reduce vibration by cancelling out unbalanced dynamic forces. The counter balance shafts have eccentric weights and rotate in opposite direction to each other, which generates a net vertical force.

The balance shaft was invented and patented by British engineer Frederick W. Lanchester in 1907.^[1][2] It is most commonly used in inline-four and V6 engines used in automobiles and motorcycles.