Counterweights are fitted against each crankpin the crankpin. The function of the counterweight is to balance the crankshaft. The counterweights serve to offset the weight of the piston and the connecting rods.
The crankshaft is said to be "internally balanced" if the counterweights alone can balance the crankshaft.
If the counterweights are not properly chosen, the crankshaft can be seriously damaged during rotation.
