Crankshaft Deflection

Each time the 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 rods. Each torque spike is like a hammer blow. In fact it hits with sufficient intensity that 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 vibration. If not adequately controlled, torsional vibration causes rapid main bearing and main journal wear and possible crankshaft breakage.

For years, vibration dampers have been mistakenly called ”harmonic balancers” which has led to a lot of confusion because this true purpose of a “harmonic balancer” is to control harmonic vibration, not to balance the engines rotating assembly. The balancing operation involves weighting the components of the reciprocating assembly, then machining each component as required to bring it within a predetermined weight tolerance. Another part of the balancing operation involves lightening or adding materials to the crankshaft counter weights so they properly counter balance the weight of the piston and rod assemblies.

On an internally balanced engine, all the counter weights are located within the oil pan that is on the crankshaft itself. In an externally balanced engine some to the required crankshaft counter weight is located on the flywheel, vibration damper or both. The fact that an engine is “externally balanced” does not mean that the vibration damper will bring the crankshaft to the proper weight tolerance. It means that a portion of the counterweight needed to counter balance the weight of the pistons and rods is located on the damper and / or flywheel. We use the Fluidamper® performance harmonic damper style. They utilize race power. Viscous Fluid (a unique silicone fluid) that resists the relative movement between the housing of the damper and the inertia ring reducing the torsional vibration. Invented by Vivratech in 1946, and introduced in 1986 to the performance automobile after market there is not a competitive racer world wide that does not use this style. Now this is included as original equipment on all diesel engines.

Control of crankshaft vibration across an engine’s entire operating range is an insurance policy that provides extended crankshaft and bearing life, less pars breakage and more consistent power output.

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