WHILE HARLEY-DAVIDSON was selling the JH and JDH to sport-minded riders, it was developing a new line of sidevalve engines. Most early motorcycle companies started out building motors with an inlet over exhaust valve configuration because it worked. Over the next few years, other valve configurations were proven to work as well, and the best researched of these was the sidevalve (also known as flathead) top end. Sidevalves, with both valves face up in a valve pocket, were proven to be reliable and powerful by the end of World War I.
A 1933 Harley sidecar outfit. The bird design on the tank was unique to 1933..
By the late 1920s, the inlet over exhaust motor design—which Harley-Davidson had used since the company started—was looking long in the tooth. The exposed intake valve gear left a light coating of oil mist on the rider’s pants. Extensive overhauls were needed at 5,000-mile intervals.
Artistic illustration from a 1931 racing program. Hillclimbing was the most popular form of motorcycle sport during this period.
Overhead valve and even overhead cam motorcycles were then racing in England and Europe, but adapting these fast, responsive motorcycles for everyday use was problematic. Valve- and valve-spring steel left a lot to be desired in the late 1920s and early 1930s, and broken valves and broken valve springs were very common. Motorcycle top-end lubrication was just beginning to be understood by engineers, and the available lubricant was, by today’s standards, filled with contaminants. Motors had to be disassembled and the carbon-filled combustion chamber scraped out on a regular basis. Given the technology of the 1920s and early 1930s, sidevalve engines were probably the best choice for everyday use.
Once Harley’s sidevalve singles had proven themselves, the company started producing 45-cubic-inch (746.33 cc) V-twins. The first of these appeared in July 1928 and although they experienced teething troubles, the problems were quickly fixed. The company, feeling confident, started building 74-cubic-inch (1207.07 cc) V-model sidevalves a year later. The introduction of this model was a disaster. All of the motorcycles sold between the August 1929 introduction and October 1929 had to be completely rebuilt by local dealers, using parts shipped from Milwaukee.
The rebuild effort restored consumer confidence in the sidevalve twins, but the creeping fingers of the Depression started to touch Harley-Davidson. Sales of 23,989 motorcycles in 1929 dropped to 18,036 in 1930 and 10,407 in 1931. New tariffs in the Commonwealth countries and Japan dried up formerly lucrative export sales. Excelsior, the third major American motorcycle factory, decided to stop motorcycle production in 1931, leaving only Harley-Davidson and Indian still standing, but this event did not stop the free-fall of sales.
In 1932, Harley-Davidson entered into a licensing agreement with the Japanese importers, Alfred Rich Child and the Sankyo family, to build V-model Harley-Davidsons in Japan. Harley sent its engineers east, where they helped the new Japanese company, Rikyo, set up a modern motorcycle factory. The licensing fees replaced some of the lost income from imports.
The 45- and 74-cubic-inch sidevalve twins were good motorcycles, but they did not supply the competitive edge Harley was looking for, even though Indian had been forced by the economic crisis to discontinue its best anti-Harley weapon, the 101 Scout. Advances in metallurgy and lubrication were making the production of an overhead-valve engine seem feasible. Despite the horrible economic situation, Harley engineers started working on an overhead-valve project.
This is a 73.73-cubic-inch sidevalve twin with high compression magnesium alloy pistons. Harley-Davidson tried several types of piston in its sidevalve twins in the 1930s. in 1933, Harley-Davidson offered bikes in five standard color combinations: black and mandarin red, olive and brilliant green, sunshine blue and white, police blue and white, and, as on this bike, silver and turquoise.
The Harley sidevalve engine: a massive, sturdy twin that can be repaired without specialist tools. It was so popular for commercial use that Harley continued to build it, despite the success of the overhead-valve Knucklehead, until 1948.
A sidevalve motor introduced by Harley-Davidson in late 1929. Each valve stem is contained in a separate round cover. The lubrication system was total loss. Harley first used the Linkert carburetor in 1934.
A second initiative was the organization of amateur racing through the American Motorcycle Association. Racing was seen as an excellent way to stimulate interest in motorcycles, and amateur races would require no investment from the cash-strapped factory. Both Indian and Harley-Davidson worked with the AMA to create Class C, which quickly became the dominant form of motorcycle competition in the United States after its introduction in 1934.
This 74-cubic-inch sidevalve V-twin was the top of the Harley line for 1934. Chrome was only used for small parts at this time. This heavily built motorcycle was able to cope with all-day riding over the poor roads of the day.
The economy improved in 1934 and 1935. The company continued building its 74- and 45-cubic-inch sidevalve twins while working on the overhead-valve machine that was to replace them. The singles were discontinued in 1934: the export markets they were destined for were gone. Good management and severe belt-tightening had gotten the company through the worst times, and things were now looking up.
The first production overhead-valve (OHV) E and EL V-twins came off the assembly line in January 1936. Unlike Harley’s disastrous introduction of the sidevalve “74”s, the rollout of the new overhead-valve V-twin went relatively well. There were problems with oil consumption for the dry-sump engine. There were mid-production changes to the kick-starter gearing and to the timing-case cover. There were three changes to the oil tank and oil line setup during the 1936 model year. But in general, Harley got it right.
A first-year Knucklehead, such as this one, is now worth a fortune. This 60.33-cubic-inch overhead-valve twin is the ancestor of the Big Twins Harley builds today. In its day, the Knuckle was one of the most powerful production road-going motorcycles available.
The other side of the Knucklehead motor. The four-speed constant mesh transmission shifted by hand. The clutch pedal is just above the footboard. In addition to the overhead-valve setup, the Knucklehead had a recirculating oil system.
For starters, the styling was so spot on that even today, over seventy-five years later, many new Harley-Davidsons look like the original 60.33-cubic-inch (988.56 cc) E that reached dealers in 1936.
The EL sport version, with 7:1 compression, produced 40 horsepower at 4800 rpm and could reach 90–95 mph—faster than was safe on most roads of the time. A four-speed state-of-the-art constant mesh transmission transferred power to the rear wheel. As with almost all motorcycles of the time, there was no rear suspension. Front springing was provided by heavy-duty chrome-molybdenum tubular leading link forks.
The Harley-Davidson E was one of the first large-capacity mass-produced overhead-valve motorcycles. Other big OHVs of the time, such as the Vincent, Brough Superior, and the Crocker, were basically custom motorcycles built in small quantities for the discerning few. The new Harley made overhead valves available to the masses.
At this point, no one referred to the E as a Knucklehead. That nickname was not given until twelve years later, when it was needed by riders and mechanics to distinguish the first version of the overhead-valve twin from the second, the Panhead introduced in 1948. But if you look at the left side of the engine, you can see the reason for the name—the top end looks like a clenched fist.
Women have always ridden motorcycles. This stylish rider is astride a 1937 Knucklehead with an aftermarket exhaust.
Harley did not discontinue the sidevalve machines—they were popular for commercial applications—and continued to build them, adding an 80-cubic-inch (1340 cc) version to the catalog in 1936. The “80” had been available by special order almost a year earlier. The combination of the E and EL sporting machines and the sidevalves worked well for the company through the rest of the 1930s.
A more casual female rider, on a 1937 Harley sidevalve.
Although most of Europe was embroiled in conflict by 1939, the United States was officially neutral. Unofficially, the country was preparing for war. Prototype military motorcycles were in the hands of the army in August 1939. The military was impressed by Harley-Davidson reliability and the relative power of the company’s 45.12-cubic-inch (739.38 cc) engine.
The economy was definitely looking up by 1941, and Harley-Davidson responded by introducing three new models: a 73.73-cubic-inch (1208.19 cc) version of the overhead-valve Knucklehead, referred to in company literature as the F and FL; and two 45-cubic-inch production racers: the WRTT with brakes and the WR without. Contemporary racers thought that brakes were dangerous on what was then the most popular type of American motorcycle competition: the flat track race around a dirt oval. The WR was specifically designed for Class C competition in these events.
A summer day and a young man on his motorcycle. Wyndham Hills is a community in York County, Pennsylvania. The logo was used by Harley Davidson on its 1941–46 models. The saddlebags, windshield, and spotlights on each side of the headlight were typical period accessories.
No date on this ad, but the Harley 125 cc two-stroke pictured has springer forks, so it was drawn between 1948 and 1951. Note that women were encouraged to ride, and no one was wearing a helmet.
On December 7, 1941, the Japanese Air Force bombed Pearl Harbor, and flat tracking and other forms of civilian sport ceased for the duration of the war. Harley-Davidson had already been significantly involved in the production of motorcycles and other vehicles for the United States military.
In January 1942, Harley-Davidson won a significant corporate victory: its WLA—the military version of the 45-cubic-inch V-twin—was accepted as the US Army’s two-wheeled vehicle. The Canadian military also bought significant numbers of Harley’s military twin, naming its version the WLC. The first US Army contract was for 31,393 motorcycles to be delivered before the end of 1943. The company worked extra shifts until February 1944.
Most civilian production was outlawed, but it was possible, especially after September 1944, to purchase a new motorcycle if you filled out the right paperwork. Police departments and workers in essential industries who needed to get to work were the most likely to get permission to buy a new ride. Some motorcycles with a two-color finish were pictured in wartime issues of The Enthusiast, Harley-Davidson’s magazine for customers.
With the end of the war in August 1945, thousands of military 45-cubic-inch twins were sold as surplus. Thousands of people were introduced to motorcycling through these military surplus bikes. Motorcycling was very popular with the returning GIs, and sales of new motorcycles climbed to pre-Depression levels. Harley-Davidson was able to buy extensive surplus machine equipment, boosting the factory’s capabilities.
The war’s end also produced two new developments on the motorcycle industry scene. Many veterans had seen, and been intrigued by the lightweight and sporting English motorcycles they had seen while serving in Europe. Triumph dealerships started popping up around the country.
At the same time, the Indian Motocycle Company, the only other American motorcycle producer, was in a downward spiral. E. Paul Du Pont, who had guided the company through the Depression and World War II, decided to sell the company. After some industrial intrigue, Indian was purchased by Ralph Rogers, who thought the future lay in lightweight motorcycles. He was right—but the lightweights he produced were both expensive and unreliable. Indian was forced to borrow large sums from an English firm named Brockhouse. Part of the deal was that Indian dealers would sell Nortons, Vincents and other British makes.
Introduced in 1948, Harley-Davidson sold thousands of this little two stroke to veterans going to college on the GI Bill. It had a foot shift, hand clutch and, after 1951, telescopic forks.
Harley-Davidson had seen the same future as Indian. Instead of building a new and untried design, Harley started with a small two-stroke, designed in Germany and acquired as war reparations. BSA in England used this design as the basis for the Bantam. Harley’s version was the Model S, a cheerful little machine that, while cheap, was built with traditional Harley attention to reliability. Over 10,000 were sold in 1948, the year they were introduced.
Ad for the Sportster H, the junior touring model, from 1958. This version of the Sportster was quickly eclipsed by the hot-rod XLCH version.
Also in 1948, a major update to the OHV reached showrooms. The bottom end of the Knucklehead was sound, proven and reliable. The top end tended to leak and run hot. The 1948 update featured aluminum cylinder heads with internal oil passages and hydraulic valve lifters. The new version of the OHV ran quieter, cleaner and cooler. The next year, the leading link forks (often called “springers”) were replaced with beefy telescopics and the front brake was enlarged. Enthusiasts started referring to “Panheads” (the rocker-box covers looked like baking pans) and “Knuckleheads.”
First-year Panhead. The Panhead motor was essentially a top end swap, offering better oil control. For the first few years, Panheads came in smaller (60.32-cubic-inch, nominally 61-cubic-inch) and larger (73.73-cubic-inch, nominally 74-cubic-inch) versions.
And then... the GIs started getting married and having babies. Harley sales started dropping. By 1954, sales were back down to pre-war levels. It did not help that a popular Hollywood movie—The Wild One—portrayed motorcyclists as law-breaking, scary hell-raisers, or that a lot of those who kept riding were veterans who had never really returned from the war. During the 1950s, Harley-Davidson often made ends meet doing subcontract work for General Motors.
There were bright spots. In 1952, Harley introduced the K model, a sidevalve midweight with foot shift and rear suspension. In 1957, the K model gained overhead valves and became the Sportster. For some reason, this new machine was designed to look like a junior Panhead. The California dealers demanded a sport version of the Sportster, and they got it the next year. The 53.9-cubic-inch (883 cc) XLCH had an excellent power to weight ratio, and, with a little tuning, could turn drag-strip times worth bragging about. Harley sold a lot of Sportsters.
In 1960, the company bought a 50 percent share in Aermacchi, an old Italian motorcycle company that was building a nice line of lightweights. These up-to-date and attractive little machines soon acquired a following.
Still—despite the efforts of Harley-Davidson and the British importers—the general public saw motorcycling as a fringe activity engaged in by people it would be best to avoid. This opinion was about to change, due to an innovative Japanese company named Honda.
This 1966 ad invites readers to become part of the “In Crowd” and enjoy the Swinging Sixties by buying an Italian-American lightweight.
A motorcycle dealer’s fantasy from 1962. Harley only sold 11,144 motorcycles that year, but in this ad, even the family kitty cat is buying a Harley-Davidson. Harley built the Topper scooter between 1960 and 1965.