The History of the Harley-Davidson JD Engine

The History of the Harley-Davidson JD Engine

Harley-Davidson has come a long way since its humble beginnings. In a small wooden shed in Milwaukee, Wisconsin, the first motorcycle was prototyped. Fast forward to today, and the company now produces nearly 200,000 road-ready hogs every year in factories around the globe. Whether you want to cruise in comfort or be part of a passion-fueled community of owners, you can have it all with a Harley.

One of the most pivotal moments in the company’s history was the creation of the JD Engine. Not only did it add some meat to the wiry pre1920s models, but it also produced more power. With a passion for all things Harley-Davidson, Competitive Distributing, a leader in Harley-Davison parts and accessories, explores the history of the iconic JD engine and why its legacy lives on.

The Early Years of Harley-Davidson

Harley-Davidson, Inc was founded in 1903 and officially incorporated in 1907 in Milwaukee, WI. The  classic motorcycle company was founded by William S. Harley, Arthur Davidson, Walter Davidson, and William A. Davidson.

Early on, the team exclusively sold engines that could be mounted on traditional bicycles. Though it was certainly an advanced concept for the time, from 1903 to 1905, Harley-Davidson’s number of sales remained in the single digits. However, in 1906, Harley and the Davidson brothers built their first factory and started producing stand-alone motorcycles. That same year, in a small factory the size of a modest American home, they manufactured roughly 50 motorcycles. 

By 1907, Harley-Davidson’s production increased to about 150 units. By 1908, that number was tripled. And, by 1909, they tripled their numbers again. Much of this surge in growth is thanks to Harley-Davidson’s ingenious idea to integrate the V-twin engine into their motorcycles. This new addition allowed their bikes to have more power and gain faster speeds. As sales continued to peak, use of the V-twin engine became Harley’s new standard.

The Introduction of the J/JD Models

While Harley-Davidson got a taste of selling bulk quantities of vehicles in 1907 to police departments and, to a slightly larger extent, the U.S. Army for the Mexican Expedition. But as America entered World War I (WWI), the U.S. Army demanded entire fleets of motorcycles. At one point, the Army’s need for motorcycles was so great that the government purchased nearly all of Harley-Davidson’s Model J bikes.

By the 1920s, Harley-Davidson became the biggest producer of motorcycles in the world, with bikes in 67 countries. Over the next decade, they’d make several significant changes to maintain their foothold in the market and to fend off the negative impacts of the looming post-war slump. In fact, Harley’s sales halved between 1920 and 1921.

In 1924 the company decided to double down on its tried and true V-twin instead of building a new engine. This decision led to an updated and upgraded J model in 1925, the JD model. Finally, the V-twin got its much-needed overhaul.

First, Harley-Davidson added a 74 cubic inch (1,212.6 cc) V-Twin engine in 1921. In 1925, they designed the iconic “teardrop” gas tank, with was first donned on the 61 cubic inch (cu in) and 74 cu in JD model pocket valve V-Twins. The teardrop gas tank ultimately became one of the most distinguishing elements of the JD model.

The 1925 Harley-Davidson JD model’s form factor gave it a whole new style. With a unique frame design, the saddle sat about three inches lower than their previous vehicles. The wheels were wider but with a smaller diameter, giving the bike a more stout and strapping profile.

The JD model also had a few other notable features. Harley-Davidson replaced the aluminum slugs with iron alloy pistons. Moreover, they added 16 Alemite fittings to the engine and gearbox to ease lubrication. Additionally, this model came standard with a:

  • Front brake
  • Foot-operated rear drum brake
  • Hard-tail rear
  • Kickstand
  • Klaxon horn
  • Luggage rack
  • Manual ignition switch with audible warning alarm
  • New height-adjustable contoured saddle 
  • Schebler carburetor
  • Single unit ignition, including a 6-volt generator battery
  • Sprung front forks
  • Tail light
  • Three-speed hand-shift, sliding gear transmission
  • Two-bulb headlight

By combining all these changes with the iconic teardrop gas tank, Harley-Davidson tapped into a look that continues to grow in popularity.

In a Henry-Ford-esque fashion, Harley-Davidson made their 1925 JD model available in only one color. But, instead of black, they chose Olive Drab.

Continuing the Legacy at Competition Distributing

Harley-Davidson, the iconic and revolutionary American motorcycle manufacturer has come a long way since its modest origins in 1903. In conjunction with its original headquarters in Milwaukee, Harley-Davidson now has factories in York, Pennsylvania; Manaus, Brazil; Bawal, India; and Pluak Daeng, Thailand.

At Competition Distributing, we believe motorcycles are more than a way to get around; they’re a way to live life. If you’re looking for parts for your JD model Harley-Davidson or any other model, please browse our store today. Let us know if you have any questions by contacting us via our contact page.