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Speaker 1: Brain with today's question, what gives a Harley Davidson motorcycle
Speaker 1: it's distinctive sound? There's no denying that a Harley Davidson
Speaker 1: motorcycle has a unique sound, especially if the mufflers have
Speaker 1: been removed. Even with the mufflers on, however, it sounds
Speaker 1: different from other motorcycles. The reason for the sound has
Speaker 1: to do with the way the engine is designed. In
Speaker 1: a basic four stroke gasoline engine, a piston goes through
Speaker 1: the intake, compression, combustion, and exhaust strokes every two revolutions
Speaker 1: of the crank shaft. When your lawnmower is idling, you
Speaker 1: can hear the pop pop pop pop pop sound of
Speaker 1: the individual strokes. What you're actually hearing is the sound
Speaker 1: of the compressed gases in the cylinder escaping when the
Speaker 1: exhaust valve opens. Each pop is the sound of the
Speaker 1: exhaust valve opening one time, and it happens on every
Speaker 1: second revolution of the crank shaft. Now think about a
Speaker 1: normal two cylinder engine. It has two pistons. The pistons
Speaker 1: are times so that one fires on one revolution of
Speaker 1: the crank shaft and the other fires on the next revolution.
Speaker 1: So one of the two pistons fires on every revolution
Speaker 1: of the crank shaft. This seems logical and it gives
Speaker 1: the engine a balanced feeling. To create this type of engine,
Speaker 1: the crank shaft has two separate pins for the connecting
Speaker 1: rods from the pistons. The pins are a hundred eighty
Speaker 1: degrees apart from each other. A Harley engine also has
Speaker 1: two pistons. The difference in the Harley engine is that
Speaker 1: the crankshaft has only one pin and both pistons connect
Speaker 1: to it. This design, combined with the v arrangement of
Speaker 1: the cylinders, means the pistons cannot fire at even intervals anymore.
Speaker 1: Instead of one piston firing every three hundred sixty degrees
Speaker 1: on the crankscheft, a Harley engine goes like this. The
Speaker 1: first piston fires, the next piston fires at three hundred
Speaker 1: and fifteen degrees. Then there's a four hundred and five
Speaker 1: degree gap, and then a piston fires. The next piston
Speaker 1: fires at three hundred fifteen degrees. Then there's a four
Speaker 1: hundred five degree gap, and then this cycle continues. At idle.
Speaker 1: You can hear the pop pop sound followed by a pause.
Speaker 1: So it's Papa, Papa, pa pap. That is the unique
Speaker 1: sound you hear. It's caused by that gap in the timing.
Speaker 1: For more on this and thousands of other topics, visit
Speaker 1: how stuff works dot com. Audible dot com is the
Speaker 1: leading provider of digital audio books and spoken word, with
Speaker 1: over one thousand titles to choose from. Audible lets you
Speaker 1: listen to your favorite books anywhere, any time. Go to
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Speaker 1: free audio book download of your choice when you sign
Speaker 1: up today.