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Primer on Servicing the Harmonic Damper
The most forgotten part of a gas or diesel engine during an overhaul is the harmonic balancer or vibration damper. These terms are synonymous. In addition, when the damper is removed and installed, it is common for the wrong procedure to be evoked, causing potential damage.
The purpose of the balancer mounted on the front of the crankshaft is to absorb the natural torsional or twisting vibrations created by the firing impulses of combustion. They are the result of the difference in speed from a piston that is in the compression stroke while another is experiencing the power stroke. It is important to note that at low rpm and high cylinder pressure (as when an engine is being lugged), the oscillation inputs to the crankshaft are at their greatest. The engineering term for this movement is crankshaft torsional vibration. If left unchecked, it can destroy an engine.
From the outside, the untrained eye would assume that the balancer is a mass of heavy steel with little to no engineering or complexity to it. That could not be further from the truth. It is an exacting and deceptively delicate piece of an engine with a great deal of engineering behind it. The balancer is actually tuned to the oscillation frequency of the engine family it is attached to. This is determined via extensive analysis and is the collective result of the engine’s torque, rpm, crankshaft design, and intended application.
Most light-duty engines (gas and diesel) will employ a balancer that uses an elastomer ring (an inertia ring) that is then surrounded by the metal enclosure. The elasticity of the rubber allows it to act as a dampening material.
In contrast, most heavy-duty diesel engines have a viscous damper that employs a silicone fluid in lieu of elastomer. The shearing of the viscous fluid is what creates the dampening action. It is generally accepted that the viscous material is better suited for the increased cylinder pressure experienced by a large diesel engine at low rpm.
Service is crucial
When removing and installing any damper design, it is necessary to use the proper tools: a damper puller for removal and an installer to put it back on.
Never hammer the damper back on the crankshaft snout. This will damage it and can also impact the crank as it is violently thrown back in its thrust against the rear main cap.
The damper is meant as a consumable. So every engine manufacturer has listed either hours or miles for its replacement, even if no overhaul is taking place.
A damper’s elastomer design loses its resiliency and the viscous style of its design through countless shear cycles. A worn-out damper often results in bearing failure along with fractures in the crankshaft, especially near the journal oil holes.