Every engine — gas or diesel — has a harmonic damper on the front of the crankshaft and while many owner/ operators and mechanics don’t give the damper much thought, all engines depend on the damper to reduce the destructive effects of the harmonic vibrations in the rotating crankshaft assembly. Quite often, service centers (even of major brands) downplay the importance of the harmonic damper and basically ignore the roll the damper plays to ensure that the engine runs at peak performance, extending the life of the engine bearings and crankshaft. The high compression of a diesel engine and ever increasing nozzle pressures coupled with the high torque at low RPM are leading contributors to increased torsional harmonic vibrations. The frequency of vibration is unique to each engine due to the differences in structural design of the various engine components.
Each time the air fuel mixture inside each individual cylinder is ignited during the combustion cycle, the explosion within the cylinder creates a torque spike that is applied to the crankshaft through the pistons and rod assemblies resulting in a torque spike that is like a hammer blow, so severe that it not only turns the crank assembly in rotation but actually twists the crankshaft ahead of its normal rotation and then it rebounds back. All of the sequences of firing, rpms, cylinder pressures and torque spikes result in the twisting of the crankshaft which is known as torsional harmonic vibration. Torsional harmonic vibrations are similar to the frequencies of a tuning fork, constantly hammering on the crankshaft which causes metal fatigue. The twisting motion of the crankshaft is similar to bending a stuck nail back and forth, eventually the metal weakens and breaks.
Unchecked torsional harmonic vibrations can cause:
• Excessive bearing wear
• Excessive gear wear or failure of accessory drives
• Fracturing or cracking of accessory drive brackets
• Broken camshafts
• Loosening or broken bolts
• Broken crankshaft
• Poor engine performance resulting in loss of HP torque
• Poor fuel economy
• Slapping or throwing of belts
• Driver fatigue
• Catastrophic engine failure
The harmonic damper is a vital, functional engine component
An effective replacement damper that consists of a free rotating inertia ring surrounded by a highly viscous silicone fluid enclosed in a hermetically sealed housing is a great choice. Silicone within the damper is 45,000 times thicker (more viscous) than 30 weight motor oil. The damper assembly is neither a totally solid steel assembly nor completely filled with oil or silicone. The silicone fluid fills a precision engineered shear gap between the inertia ring.
How the damper works
When torsional vibrations occur with every power stroke of the engine, the outer housing rotates with the rotation of the crankshaft while the inertia ring inside the housing moves out of phase with the housing. This relative motion between the inertia ring and the housing causes the inertia ring to shear through the silicone damping the harmonic vibration. The shearing action of the inertia ring through the silicone is what allows the inertia ring to tune to the frequency of vibrations at any given operating parameter of the engine. Contrary to popular belief, the harmonic damper does not balance the engine; it removes the harmonic vibrations from the engine.
The properties of silicone result in high energy dissipation. It is the silicone that allows the inertia ring to rotate freely, tuning to the harmonic vibration frequency at any RPM, however in heavy-duty applications the silicone does wear out. (A viscous type performance damper as used in performance racing applications will never be worked hard or long enough to wear out.)
Why the heavy duty damper wears out
Over time, the constant lugging, torque, heat and hours of operation on heavy duty diesel applications makes the silicone start to revert to a solid state. As this progresses, the silicone becomes thicker; the reaction time and shearing motion of the inertia ring begins to slow down, which inhibits the ability of inertia ring to tune to the different harmonics of the engine throughout the RPM operating range. When a damper reaches the end of its life, the silicone will convert to a solid paste — locking up the inertia ring — usually resulting in severe harmonic vibration and potential catastrophic engine failure resulting from a broken crankshaft.
While recommended replacement intervals vary depending on the engine manufacturer, the average life is approximately 500,000 miles or 15,000 hours of operation or at every in-frame or major overhaul.
Worn out dampers
Take a look at the worn out damper pictured above. The dark coloring is coagulated silicone collecting in pockets in the shear gap. The bright areas are dry areas of bare steel with no silicone present. The silicone in this damper has deteriorated to nearly a solid paste and the inertia ring was close to completely locked in place. At this stage, the reaction time of the inertia ring would have been greatly reduced and could have possibly caused the inertia ring to intermittently stick and then break loose causing severe harmonic vibration conditions.
This damper came from an engine that had been rebuilt but the damper was not replaced. The end result was a broken crank. The deteriorated condition of this damper was clearly a major factor in the failure of the crankshaft. It also contributed to severe wear of the bearings and crankshaft before the rebuild and if it had been replaced during a regularly scheduled or routine preventive maintenance the associated metal fatigue from the harmonic vibrations would have been greatly reduced or eliminated. The fact is that uncontrolled harmonics cause metal fatigue.
The damper should be visually inspected for signs of abuse, such as dents or leaking around the weld. If there is a dent in the damper, it is likely that the shear gap has been compromised, reducing the shearing action or locking up the inertia ring.If there is a leak, it is usually caused by the damper being dropped or abused during installation or removal. Never use a hammer to install or remove a viscous damper. Since the silicone is thick, it will not look like oil running out but will be a tacky consistency right at the point of the damage.
Spinning the damper in a lathe will not determine if it is functional. Testing of a viscous type damper takes proprietary and specially designed equipment to test for functionality and even then the remaining life is difficult to determine.
It is always best to follow the guide lines of actual service in miles or hours.
Consider replacing the vibration damper as an insurance policy against a future broken crankshaft. It’s not worth the risk and never let anyone talk you out of replacing the damper if it falls into any of the replacement criteria.
For more information, please contact Vibratech TVD, LLC, 180 Zoar Valley Road, Springville, NY 14141. Call 716-592-1000 or go online: www.vibratech.com.
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