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