Balancing Shafts in Engines

Balancing Shafts in Engines are used to offset the vibration due inherent imbalances in IC Engines. 

In engines with certain cylinder configurations, there is an inherent balance due to the firing of the cylinders.  For instance, V engines with six cylinders are inherently unbalanced as they have an odd number of cylinders on each bank. 

Four cylinder engines are another configuration where inertial forces cause vibrations.  These vibrations are offsets by two balancing shafts which rotate at twice the speed of the engine in the opposite direction.  The balancing shaft contains counterweights.  They are located in the crankcase of the engine