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Old 01-28-2008, 04:14 PM   #64
mach007
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Join Date: Dec 2007
Location: Palm Springs, Cali
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Re: Under Drive Pulleys..and the problems they cause.

Yes. Just some food for thought.


Torsional vibration is a concern in the crankshafts of internal combustion engines because of several factors.

Alternating torques are generated by the slider-crank mechanism of the crankshaft, connecting rod, and piston.
The motion of the piston mass and connecting rod mass generate alternating torques often referred to as "inertia" torques
The cylinder pressure due to combustion is not constant through the combustion cycle.
The slider-crank mechanism does not output a smooth torque even if the pressure is constant (e.g. at Top Dead Center there is no torque generated)
Engines with several cylinders can have very flexible crankshafts due to their long length.
There is inherently little damping in a crankshaft to reduce the vibration
If torsional vibration is not controlled in a crankshaft it can cause failure of the crankshaft or any accessories that are being driven by the crankshaft (typically at the front of the engine, the inertia of the flywheel normally reduces the motion at the rear of the engine).

This potentially damaging vibration is often controlled by a torsional damper that is located at the front nose of the crankshaft (in automobiles it is often integrated into the front pulley). There are two main types of torsional dampers.


Tuned absorber type of "dampers" often referred to as a harmonic dampers or harmonic balancers (even though it technically does not dampen or balance the crankshaft). This damper uses a spring element (often rubber in automobile engines) and an inertia ring that is typically tuned to the first torsional natural frequency of the crankshaft. This type of damper reduces the vibration at specific engine speeds when an excitation torque excites the first natural frequency of the crankshaft, but not at other speeds.

Over time, the energy dissipating (rubber/clutch/fluid) element can deteriorate from age, heat, cold, or exposure to oil or chemicals. Unless rebuilt or replaced, this can cause the crankshaft to develop cracks, resulting in crankshaft failure. (have these ever been looked into as a factor?)
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