LO 8-10 Identify and describe the types of crankshaft vibration

Elastomeric Dampers

Elastomer dampers refer to vibration dampers that use rubber as the primary material to absorb harmonic vibrations and reduce torsional stress on the crankshaft. These are made of three parts: The inner hub is attached to the crankshaft, which connects to a heavier, outer iron inertia ring through a rubber or elastomeric ring Figure 67. The damping action occurs as the outer ring oscillates alternately with speed changes in the inner ring’s movement. For example, when the crankshaft slows, the inner ring slows too, but speed inertia of the outer ring will stretch the rubber ring that connects the two metal rings. When the inner ring slows down, the outer ring transmits stored inertial force through the rubber ring to speed up the inner ring. The opposite action occurs as the inner ring accelerates and transmits the sudden speed change through the rubber ring to the outer ring. The outer ring will resist the speed change, thus slowing down the inner ring. The elastomeric damper is tuned to vibrate out of phase with the lowest torsional frequency of the engine. The rubber ring inside the damper also has the ability to absorb harmonic vibrations, much like placing a heavy glove over a ringing bell. Alignment and verification of the proper operation of the two inertia rings is confirmed by a mark scribed in the face of the outer and inner rings. If the marks are not aligned, the rings have debonded from the elastomer ring and the damper is defective Figure 68. Damper runout, when measured with a dial indicator, should be compared with OEM specifications. A damper with a rubber ring that is twisted or falling out of the inertia ring is also likely defective.

FIGURE 08-67: An elastomeric damper’s outer inertia ring and inner hub move in opposite directions during a torsional impulse. The movements help minimize changes to crankshaft speed by accelerating the crank when the ring slows and slowing the crank when the ring speeds up.

FIGURE 08-68: When inspecting a vibration damper, alignment marks on an elastomer damper must line up.