Each time a cylinder fires, a force acts upon the crankshaft, causing it to twist. But this force also causes vibrations in the crankshaft, and at certain frequencies, the shaft can resonate, which makes the vibrations even worse. These vibrations from the engine can become too much for the crankshaft to bear, causing it to fail. This is where the harmonic balancer comes in. It is bolted at the front end of the crankshaft to help absorb vibrations.