The crankshaft, regarded as the "backbone" of the engine, serves to change the reciprocating motion of the piston into rotary motion and handles the entire power output.

The torsional vibration absorbers of reciprocating piston engine crankshafts are the earliest and most commonly used kind of damped dynamic vibration absorbers.

However, diesel engine is a typical reciprocating machine, its monitoring and diagnosis are very difficult because of its complex structure.