Are you familiar with the term ‘torsional vibration’? Well, torsional vibration is simply a periodic vibration which would result from the twisting of an object around its axis. In your Mini engine, this vibration would be expected to originate from the crankshaft as the engine tries to turn it. Excessive torsional vibration, however, is unwanted because it may cause various damages not only to the crankshaft but to the engine itself. Simply put, each time that the air/fuel mixture is ignited within the engine’s cylinders, the combustion causes an extreme amount of cylinder pressure. This cylinder pressure is applied to the pistons and then to the connecting rods and is transferred to the crankshaft. This downward force makes the crankshaft turn. Because this pressure is so great, it produces a torsion vibration from the pistons and incorporated with the crankshaft vibrations causes the crankshaft to twist and deflect causing an action referred to as "tortional harmonic vibration."
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