Introduction to How Harley-Davidson Works

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100th anniversary harley emblem
Photo courtesy Harley-Davidson Motor Company
Harley-Davidson 100th Anniversary Tank Emblem with Chrome Bar & Shield

How do you write about Harley-Davidson? When someone mentions the words "Harley-Davidson" several things come to mind:

  • The company that produces motorcycles.
  • The actual motorcycles that the company produces.
  • The history and tradition that surround the company and the products.
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And, there's something else, too -- the aura of Harley-Davidson. Some call it Harley mania. Others refer to it as Harley culture. If you're having a hard time understanding this concept, just consider this: Every year, hundreds of thousands of Harley-Davidson enthusiasts converge on towns like Sturgis, S.D. (August), Myrtle Beach, S.C. (May) and Daytona Beach, Fla. (March) for an entire week of partying and vendor demos. These folks ride their bikes hundreds if not thousands of miles just to participate.

Unlike any other major brand of bike, there's a certain something that Harley-Davidsons carry with them. It could simply be the sound of a large V-Twin engine through straight pipes at full throttle -- this has certainly been glamorized in dozens of movies. But we think it's more than that. Call it mystique if you like. There is definitely something to it.

a 2003 Harley Screamin' Eagle Softail Deuce
Photo courtesy Harley-Davidson Motor Company
The 2003 Screamin' Eagle Softail® Deuce, shown here in custom paint colors - Centennial Gold and Vivid Black.
See more motorcycle pictures.


In this article, you will have a chance to learn about the Zen of the Harley-Davidson from a HowStuffWorks perspective. We will cover the evolution of the engines, the current product line and the customization process. The next time you pull up alongside a Harley-Davidson, you'll see it in a completely different way.

Before you can begin to understand the Harley mystique, you'll need to have a basic understanding of how motorcycles work.

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­At its very simplest, a motorcycle is a bicycle with an engine. If you go all the way back to the beginnings of Harley-Davidson Motorcycles in 1903, a motorcycle is exactly that. The first production Harley-Davidson was a bicycle with a slightly modified frame to make the engine easier to mount. A leather belt carried the power from the engine to the rear wheel. This motorcycle had pedals, so you could pedal it like a bicycle if you wanted to. It also had a normal coaster brake in the rear hub that you could apply with the pedals (by pedaling backwards), just like you would on a normal one-speed bicycle today.

the first Harley
Copyright Harley-Davidson Archives
Photo courtesy Harley-Davidson Motor Company Archives
The first Harley-Davidson was basically a motorized bicycle.


That original Harley-Davidson motorcycle had a 24.75 cubic inch (405 cc), single-cylinder, air-cooled engine with an F-head valve configuration. The engine weighed 49 pounds.

Today a motorcycle does not really look at all like a bicycle. Both vehicles have two wheels, but that is where the similarity ends. Read on to learn about today's motorcycles.

A Basic Motorcycle Today

Two things worked in concert with each other to make motorcycles look so large today:
  1. The engine grew bigger and bigger, so the motorcycle grew bigger to hold the engine and support the weight. As the motorcycle grew heavier, the wheels and tires got bigger and stronger to support the weight, as did the brakes, the frame, etc. The fuel tank also expanded to give the larger engine the fuel it needs.

  2. With growing engine sizes, motorcycles became much faster and could travel much longer distances. Higher speeds meant the addition of a transmission. Rider comfort in the form of bigger tires, suspension systems, seats and so on were added to make the ride better. Additional speed also makes the tires more important for performance, so the tires got wider.
You can see all of the advanced motorcycle features in the motorcycle pictured below.

a Harley-like custom motorcycle
Today's motorcycles are very distant relations to the motorized bicycles of the past.

This motorcycle is not a Harley -- it is a Harley-like custom motorcycle that strips a modern motorcycle down to its bare essentials. For example, this motorcycle has an engine and a transmission:

the two-cylinder V engine of a Harley-like custom motorcycle
88 cubic-inch (1,450 cc), two-cylinder V engine

the exhaust pipes of a custom motorcycle
The stainless steel exhaust pipes are connected directly to the engine's cylinders.

In this case the engine is an 88 cubic-inch (1,450 cc), two-cylinder engine. The cylinders are arranged in a V configuration with a 45-degree angle to the V. The engine uses dry sump lubrication, and the external tank for the oil mounts above the transmission. Exhaust is simply a pair of stainless steel pipes connected to the exhaust port of each cylinder. There is no muffler or catalytic converter of any kind.

The transmission sits just behind the engine. It is a 6-speed sequential manual gearbox. The engine transmits its power from the crankshaft to the transmission through a primary drive. The power then moves from the transmission to the rear wheel through the final drive, which in this case is a chain as seen in this photo:

the final drive of a custom motorcycle
The primary drive on this motorcycle is a very wide Kevlar/rubber belt. The large chain is the final drive.

All the engine's power ends up going to the back wheel.

motorcycle back wheel
The engine's power ends up going to this extremely wide back wheel.

You can also see the rear disk brake, as well as the back portion of the frame. In the above photo, as well as the photo below, it's obvious that motorcycle frames can be extremely simple.

a motorcycle frame
This motorcycle frame has a simple design. Because it has no rear suspension, it is called a "hard tail."

The frame is just a few steel tubes bent and welded together. See this page for photographs of several different frames. This motorcycle has no rear suspension and is therefore called a hard tail.

The front fork, the only suspension component on this bike, is located at the front end of the motorcycle.

motorcycle front fork
The front fork is the only suspension component on this bike. It can compress to act like a shock-absorber.

You can see that the front wheel is much smaller than the rear. There is a single disc brake at the front. The front fork can compress to absorb shock. At the top of the front fork are the handlebars and headlight.

Certainly this motorcycle is not as simple as the first Harley-Davidson in 1903, but it is not super-complicated either. This is minimalist gasoline-powered transportation. So, how does a Harley compare to this basic-bike? Let's take a look.

What is a Harley?

the 100th anniversary emblem
Photo courtesy Harley-Davidson Motor Company
Harley-Davidson 100th Anniversary Tank Emblem with Chrome Bar & Shield
You can get all kinds of motorcycles today, mostly from Japanese manufacturers like Honda, Yamaha and Kawasaki. But, most folks would argue that none of them have the aura, tradition, name recognition or mystique of the motorcycles from Harley-Davidson. You're probably wondering what it is that is so unique about a Harley, so let's start with the engine.

Here are some of the distinguishing characteristics of the engine:

  • Until 2001, Harley-Davidson had been devotedly married to the two-cylinder V-twin design with a 45-degree angle between the cylinders.
  • The engines are air-cooled.
  • The engines have overhead valves that are activated by camshafts in the crankcase.
  • Oil comes from a dry sump lubrication system.
  • Harley engines have a long stroke. This means that the engines are low-revving and have lots of torque. Redline is typically in the 5,000 RPM range.
  • Harley engines have a single-pin crankshaft, giving these engines a unique sound. We'll have more on that distinctive sound in the next section.

In 2001, Harley made what was for it a radical move. A new engine called the Revolution™ engine was introduced, to be used in the upcoming 2002 VSRC. The Revolution is still a V-twin but it has a 60-degree V, is water-cooled, has 4 overhead camshafts and is high-revving (9,000 RPM redline).

the Harley Revolution engine
Photo courtesy Harley-Davidson Motor Company
The Revolution™ engine is currently used on only one Harley production model -- the VSRC. Both the 2003 VRSCA V-Rod™ (shown here) and the 2002 VSRC sport the Revolution™ engine.

Beyond the engine, Harley motorcycles themselves have their own look and feel. Because of the big engines, Harleys tend to be big bikes. The biggest Harleys weigh close to a thousand pounds (453.6 kilograms) and tend to incorporate retro styling. We'll discuss the new engine in more detail a little later on in this article.

Next, we'll learn about the Harley mystique and its distinctive sound.

Harley in the Movies
From "Easy Rider" to "The Terminator 2" to "Mission: Impossible II" -- motorcycles have been making the movie scene for decades.
dvd cover of 'harley davidson and the marlboro man'
Photo courtesy Amazon.com
In fact, Harley-Davidson gets top billing in the 1991 movie entitled "Harley Davidson and the Marlboro Man." Featuring two main characters: one named for the famous motorcycle company and the other a popular cigarette brand, this movie continues to have a following. Some other products are also given a nod in the film -- there's a character named "Virginia Slim" (like the cigarettes) and another named after the famous whiskey "Jack Daniels."

The Harley Mystique and the Distinctive Sound

Where does the Harley mystique come from? Think about a Marlboro cigarette. It's simply a bit of tobacco wrapped in paper. There are hundreds of other brands of cigarette that are nearly identical, but the Marlboro brand has mystique. Part of it comes from image advertising, but the other part is cultural. The people who smoke Marlboro cigarettes tend to be a certain type of person. Because they advertise and reinforce the brand image, they in turn attract more of their kind to the brand -- and so on.

In the case of Harley-Davidsons, although some amount of advertising is done, far more of the brand image comes about in other ways:

  • The use of Harleys in the movie and television industry.
  • The huge Harley rallies that can attract over 100,000 bikers.
  • The people who ride Harleys, and the image they project in public.
These elements along with a few others create a resonating, grassroots type of promotion that is extremely rare, but fascinating when it happens. This begins to convey the Harley mystique. Now let's discuss something else that resonates -- the telltale Harley sound.

There is no denying that a Harley-Davidson motorcycle has a unique sound, especially if the mufflers have been removed. The sound is part of the mystique. The reason for the sound has to do with the way the engine is designed.

the 2002 Ultra Classic Electra Glide
Photo courtesyHarley-Davidson Motor Company
Favorably fitted and ready for the road, the 2002 Ultra Classic® Electra Glide® is equipped with the Twin Cam 88® Engine, air-adjustable rear touring suspension and triple-disc brakes.

If you have read the HowStuffWorks article How Car Engines Work, then you know how a basic four-stroke gasoline engine operates. A piston goes through the intake, compression, combustion and exhaust strokes every two revolutions of the crankshaft. When your lawn mower is idling, you can hear the pop-pop-pop-pop sound of the individual strokes. What you are 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 crankshaft.

In a two-cylinder, horizontally opposed engine, the pistons are timed so that one fires on one revolution of the crankshaft and the other fires on the next revolution -- so one of the two pistons fires on every revolution of the crankshaft. This seems logical and gives the engine a balanced feeling. To create this type of engine, the crankshaft has two separate pins for the connecting rods from the pistons. The pins are 180 degrees apart from one another.

A Harley engine has two pistons. The difference in the Harley engine is that the crankshaft has only one pin, and both piston rods connect to it. This design, combined with the V arrangement of the cylinders, means that the pistons cannot fire at even intervals. Instead of one piston firing every 360 degrees, a Harley engine goes like this:

  • A piston fires.
  • The next piston fires at 315 degrees.
  • There is a 405-degree gap.
  • A piston fires.
  • The next piston fires at 315 degrees.
  • There is a 405-degree gap.
And the cycle continues.

At idle, you can hear the pop-pop sound followed by a pause. So the sound of a Harley is pop-pop...pop-pop...pop-pop. That is the unique sound of a Harley-Davidson motorcycle.

The Name Game
William Davidson, Walter Davidson, Arthur Davidson and William Harley
Photo courtesy Harley-Davidson Motor Company Archives
From left to right: William Davidson, Walter Davidson, Arthur Davidson and William Harley.
The Harley-Davidson Motor Company got its name from founders William S. Harley and Arthur Davidson. In time, Davidson's brothers, William and Walter, joined the company.

According to the Harley-Davidson Archives, Harley's name comes first because "it was his drafting, designing and testing that made the first motorcycles ever produced by the young company a possibility." The men included the hyphen in the name so that it would be clear that the company had two founding fathers, not just one.

Harley Engines

We live in a world where computer technology changes on a daily basis. Japanese motorcycle companies tend to create new engine designs every year. Car lines are completely revamped every three or four years. Then there is the Harley-Davidson Motor Company.

the Harley-Davidson Open Road Tour at the Altanta Motor Speedway
Photo courtesy Harley-Davidson Motor Company
As part of the 100th anniversary festivities, Harley-Davidson went on tour. This photo is from the Open Road Tour stop in Atlanta: Harleys as far as the eye can see outside the Atlanta Motor Speedway.

Harley-Davidson seems to work on a completely different clock, with new engine designs arriving every 15 years or so. Between 1936 and 2003, engine designs released by Harley represented a constant tweaking of the same basic V-twin, 45-degree, air-cooled engine design. In 2001, Harley released its first truly new design in a commercial motorcycle, yet it was still a V-twin. If you ignore the first few years of the company's history as a period of experimentation, there really have been only seven major engine revisions during the company's 100 year existence:

  • Flathead engines - Manufactured between 1929 and 1974. Flatheads did not have overhead valves. Instead, the valves ran alongside the engine and opened upwards into a chamber beside the combustion chamber. The advantage of a flathead was simplicity -- no pushrods or rocker arms, and the head was a simple casting with a hole in it for the spark plug. A typical flathead engine had a displacement of 45 cubic inches (742 cc) and produced about 22 horsepower.

a flathead engine
Basic design of a flathead engine.

  • Knucklehead engines - Manufactured between 1936 and 1947. The knucklehead came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations able to produce 40 and 45 horsepower respectively.

  • Panhead engines - Manufactured between 1948 and 1965. The panhead also came in 60 cubic inch (990 cc) and 74 cubic inch (1,200 cc) variations and produced 50 and 55 horsepower respectively. Big differences between the knucklehead and the panhead included aluminum heads on the panhead and internal oil lines, as opposed to external lines on the knucklehead.

  • Shovelhead engines - Manufactured between 1966 and 1985. Shovelheads displaced 74 cubic inches (1,200 cc) and produced 60 horsepower.

  • Evolution engines - Manufactured between 1984 and 1999. Displacement is 81.8 cubic inches (1,340 cc), and the engine produces 70 horsepower. Although the Evolution 1340cc is no longer in production, the Sportster® model line of motorcycles receives Evolution engines with 883 cc and 1200 cc displacements (manufactured 1986 to present).

    the 2003 XL Sportster 883R
    Photo courtesy Harley-Davidson Motor Company
    This 2003 XL Sportster® 883R is equipped with a rigid mount 883cc Evolution® engine.

  • Twin Cam 88 engines - Manufactured starting in 1999. The Twin Cam gets its name from the fact that it has two cams in the crankcase to activate the valves. At 88 cubic inches (1,450 cc) of displacement, it is the largest production Harley motorcycle engine, and it produces 80 horsepower. The engine remains air-cooled, and uses overhead valves activated by pushrods. The 88B version of the engine, which came out in 2000, contains counterbalancing shafts to reduce engine vibration.

  • Revolution engines - Manufactured starting in 2001. The Revolution engine is currently used on only one Harley production model -- the VSRC. While all of the engines previously mentioned are largely the same and represent incremental improvements, the Revolution engine is different. This engine is water-cooled rather than air-cooled and its V angle is 60 degrees rather than 45. It has four overhead cams rather than two cams in the crankcase and is fuel injected. This engine is smaller -- only 69 cubic inches (1,130 cc). It has a much shorter stroke, allowing it to rev to 9,000 RPM, and it produces 115 horsepower.

the Revolution Engine
Photo courtesy Harley-Davidson Motor Company
The Revolution™ Engine

The Harley Product Line

Over the years there have been hundreds of Harley-Davidson models and variations, but if you are going to speak Harley-ese, there are certain model names in the current lineup that you need to be able to recognize. Here are the biggies:
  • The Sportster - Harley's entry-level bike. It is lighter and sportier than most Harleys, hence the name. The 2003 Sportster comes in seven different variations. It is 88 inches long, weighs about 500 pounds and prices start around $7,000 or so.

    the 2003 FLSTF Fat Boy
    Photo courtesy Harley-Davidson Motor Company
    This "Terminator-Worthy" 2003 FLSTF Fat Boy® is equipped with a rigid mount, 1450cc Twin Cam 88B™ balanced engine.

  • The Softail - A general-purpose bike. It is about 95 inches long and weighs about 650 pounds. Prices fall between $14,000 and $19,000. Recognizable names in this line are the "Deuce," the "Fat Boy" (made famous in the movie "Terminator 2"), and the "Springer Softail," so named because of the sprung front fork (rather than a hydraulic fork).

  • The VRSC - This is currently the only production Harley-Davidson motorcycle using the Revolution engine. It is 94 inches long and weighs about 600 pounds and is priced at about $19,000.

    the 2002 VRSC
    Photo courtesy Harley-Davidson Motor Company
    This 2002 VRSC is equipped with the new Revolution™ engine.

  • The Dyna Glide - This classic Harley chopper is 94 inches long and about 630 pounds, with prices ranging from $13,000 to $18,000.

  • The touring bikes - The touring bikes include the "Road King," the "Electra Glide" and the "Ultra Classic." These bikes are all 94 inches long and weigh between 700 and 800 pounds. These bikes all have saddlebags and other touring trim. Prices start at about $15,000 and head toward $22,000.

    The 2003 FXDWG Dyna Wide Glide
    Photo courtesy Harley-Davidson Motor Company
    This 2003 FXDWG Dyna Wide Glide® is equipped with a vibration-isolated, Twin Cam 88® engine.

The Harley-Davidson Web site has full descriptions, spec sheets, pricing and payment calculators, etc. to let you learn all about the different models.

Customizing and Aftermarket

Charitable Choppers!
The Harley-Davidson Motor Company has raised more than $50 million since 1980 for the Muscular Dystrophy Association (MDA). As part of the company's 100th anniversary celebration in 2003, Harley-Davidson raised $7.3 million in that year alone.
Source: Harley-Davidson Web site
A strange thing has happened in the Harley marketplace.

Just like people enjoy customizing their cars, people enjoy customizing their Harley-Davidson motorcycles. The customizations can be simple, like putting on a different exhaust system, or they can be radical, like putting on chopper-style forks.

The supply of parts for customization is called the aftermarket. There are thousands of companies producing aftermarket Harley-Davidson parts.

Over time, the Harley aftermarket has grown. Harley-Davidson has helped this process by being slow to change. The aftermarket now produces every single part on a Harley motorcycle in multiple forms: engines, transmissions, frames, forks, brakes, wheels, gas tanks and so on can all be purchased in the aftermarket.

Harley 2003 FLHRSEI2 Screamin' Eagle Road King
Photo courtesy Harley-Davidson Motor Company
Who needs aftermarket add-ons? You don't if you've got the 2003 FLHRSEI2 Screamin' Eagle Road King® parked in your garage!

What this means is that you can now go to suppliers, buy all the parts you need and assemble, completely from scratch, your own custom Harley-like machine using off-the-shelf parts. You buy an aftermarket frame, an aftermarket engine, an aftermarket transmission, and so on. Once you have it all together, you have a something that looks a lot like a "Harley," but it does not include a single Harley-Davidson part.

An aftermarket supplier like Cyborg Cycles is typical of the kind of company that can sell you all the parts. Cyborg caters to the build-your-own marketplace. You can also buy complete motorcycle kits including every part you need to assemble a Harley-like clone yourself. If you have never built a custom motorcycle before, a kit can take a lot of the guesswork out of the process and improve your chances of success.

You can literally do anything you want in the Harley aftermarket. You can spend anywhere from $10,000 to $100,000 on a bike that has the exact features and "look" that you want.

To learn more about Harley-Davidson motorcycles and the Harley aftermarket, see the links on the next page.

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