Lesson 1/Learning Event 1
As you can see, the order in which the cylinders produce power strokes is determined by the crankshaft throw
arrangement. This order is called the firing order of an engine and is given by a group of numbers. For
example, the firing order of a six cylinder engine is 153624. These numbers mean that the engine fires or
produces power strokes beginning with cylinder No 1, then No 5, No 3, and so on.
Some crankshafts are quite long and tend to twist when some pistons are on their power strokes. This causes a
shaking or vibrating of the shaft that is called torsional vibration. To understand how this can happen, think of
the crankshaft as being made of rubber. When the front cylinder fires, it tries to turn the crankshaft very
quickly. The heavy flywheel, which is bolted to the opposite end of the crankshaft, resists this sudden
movement which causes the crankshaft to wind up or twist. When the power stroke ends, the crankshaft will
unwind. The repeated winding and unwinding causes the torsional vibration.
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