Crankshaft Deflection -
The Invisible Enemy

Each time the air/fuel mixture inside a cylinder is ignited, the combustion that results creates a torque spike - an extremely rapid rise in cylinder pressure. This pressure, applied to the top of the piston, becomes the force that is applied to the crankshaft through the connecting rod. Each torque spike is like a hammer blow. In fact, it hits with sufficient intensity that it not only causes the crankshaft to turn, it actually deflects or twists it. This twisting action and the resulting rebound (as the crank arm snaps back in the opposite direction) is known as torsional harmonic vibration. If not adequately controlled, torsional vibration causes rapid main bearing and main journal wear and possible crankshaft breakage.

Fortunately, harmonic vibration can be controlled by a vibration damper - which is also called a harmonic damper or erroneously a "harmonic balancer". The main purpose of a "harmonic damper" is to control harmonic vibration, not necessarily to balance the engine's rotating assembly.

Not All Dampers are Created Equal

Although harmonics occur over a broad range of engine speeds, rubber and elastomer-type dampers are frequency sensitive - they are tuned only to control harmonic vibrations that occur within a narrow band of rpm. However, there is more than one area within the operating range of a performance engine that critical harmonic vibrations occur, therefore, elastomer dampers may not be effective. The resulting lack of vibration control could prove to be very destructive. Rubber is also a poor dissipator of heat, and dampers by their nature create heat as they work to reduce vibration. As the rubber gets hotter, it does not work as well. Second, rubber breaks down when exposed to the elements. Over time, the rubber strip can crack and begin to deteriorate due to age and exposure. This can lead to inertia ring slippage, damper failure, and uncontrolled torsional vibration, which leads to costly parts breakage.

For more information on torsional vibration and the difference between Fluidampr and elastomer dampers, click here.