If you had a need for speed, the Harley-Davidson JDH, arguably the first Superbike, was the machine for you.
1929 Harley-Davidson JDH
Claimed power: 29hp @ 4,000rpm
Top speed: 85mph
Engine: 1,207cc (74.7ci) air-cooled IOE 45-degree V-twin, 3.424in x 4in bore and stroke, 6.5:1 compression ratio
Weight (wet): 408lb (185kg)
Fuel capacity: 4.75gal (18ltr)
Price then/now: $370/$45,000-$65,000
Is the Harley-Davidson JDH the first Superbike? When motorcycle magazines started talking about Superbikes in the late Sixties they were big-bore motorcycles with speed and panache, bikes that broke quarter-mile times and turned heads with equal ease. The implication in the excited magazine articles was that this type of machine was a recent development. As Exhibit A in the “It Ain’t Necessarily So” department, Motorcycle Classics presents the Harley-Davidson JDH, the machine that helped the Twenties roar.
The JDH has been the stuff of legends for over 80 years. It weighed about 408 pounds, was powered by a 74-cubic-inch V-twin and was good for 85mph in standard trim — 100mph if you matched the manifold to the cylinder heads and knew how to tune the beast. Based on factory racing designs, a JDH would blow away almost everything else on the road, two wheels or four, when it was introduced in 1928. In the late Twenties, if you had a need for speed, a JDH was the cat’s pajamas.
The bike that became the Harley JDH took shape in the period around World War I, a time when Harley-Davidson’s archrival Indian concentrated on selling bikes to the American expeditionary forces, starving its dealers and leaving the field open for Harley to expand. In 1915, Harley sold over 16,000 motorcycles, mostly 61-cubic-inch twins. Good sales led to improvements in the product. An electric headlight and taillight were offered as an option, as well as Harley’s first 3-speed transmission. The oiling system was improved, and Harley guaranteed its twins would develop 11 whole horsepower.
The valve gear on Harley’s 1915 V-twins was inlet over exhaust, with the intake valve operated by a cam lobe in the crankcase via a long pushrod and an exposed rocker to the valve, which sat atop a valve pocket cast into the cylinder. The exhaust valve, located in the bottom of the valve pocket, was also moved by a cam lobe, but with a much shorter pushrod. This inlet-over-exhaust top end was messy — oil mist got over everything from the exposed valves. Yet it worked, and worked well, and Harley used this system for the next 15 years.
In 1917, in a bow to the doughboys of World War I, all Harleys were painted a shiny olive drab livened up by fancy pinstriping instead of the gray used previously. Except for two years when Harley tried a different green, the stock color on all its bikes through the early Thirties was olive drab.
In 1919, Harley started building racers with two cam gears (with two lobes on each gear) on separate shafts instead of having all four cam lobes mounted on one gear shaft. The idea was to reduce reciprocating weight and reduce the length of the cam followers. The two-cam engines could rev higher than comparable Harley single cam twins, and they were fast and reliable in a racing environment. In the beginning, two-cam engines were only available to factory racers.
In 1920, Harley-Davidson finished constructing the largest motorcycle plant on the planet, and started building its own generators and coils. By then, the company employed 2,400 people. Only 14 years earlier, the Harley shop was so small it was picked up and moved back a couple of feet to avoid encroaching on a railroad right of way.
The American motorcycle market had changed considerably in those 14 years. When Harley started production, most motorcycles were bought for economical transportation. With the advent of the Ford Model T, an increasing percentage of the economical transport crowd abandoned their bikes for four wheels. Most American motorcycle manufacturers went out of business, and the few left got by through a combination of overseas exports, sales to sport riders, urban commercial sales and police sales. A major market for Harley-Davidson was motorcycle-based commercial delivery vehicles, which could thread through crowded city streets. The commercial purchasers demanded reliability, and police purchasers also wanted power.
In 1921, Harley came out with its first 74-cubic-inch V-twins. Harley continued to build two-cam racers, refining the design every year, but they were still not available to the general public. Some dealers with an “in” to the factory were able to get one, but the hot engines were out of reach for the average enthusiast.
Good times led to an increase in the number of sport riders. Starting in the mid-Twenties, Harley-Davidson pushed the idea of motorcycle clubs all over the country. Dealers were encouraged to sponsor clubs and provided with literature on how to get clubs started. Numerous enthusiast clubs had sprung up in the early years of the century, but many had fallen by the wayside after the get-to-work riders bought Model Ts.
However, the combination of general prosperity and Harley’s push for club formation brought new riders into the fold. Harley dealers found that supporting clubs and social events was good for business: An active local motorcycle club meant increased sales of motorcycles in general and sport bikes in particular. Harley’s sales numbers, which had been stagnant, started to rise, and the sales leaders were the faster twins. By 1927, Harley was selling over 18,500 bikes a year, over 13,000 of which were the Model J 61-cubic-inchers and the Model JD 74s. However, these were basically commercial machines; many sport bike enthusiasts preferred Indian 101 Scouts and Excelsior 45-cubic-inch Super X twins, while still others bought Henderson Fours. Harley felt the need to offer a sporting machine to compete.
In 1928, Harley finally broke down and started offering road going versions of its two-cam engines to the general public. Available in JH 61-cubic-inch and JDH 74-cubic-inch versions, the production two-cammers had the same general setup as the contemporary two-cam racers. The twin cams acted through tappets to actuate the overhead intake valve pushrod and the exhaust valve. The intake valves had double valve springs and the springs on the exhaust valves were uncovered for increased cooling. Lifter blocks on top of the right case helped route oil back to the crankcase and pistons were domed magnesium alloy, producing a compression ratio of 6.5:1.
Harley offered a sports package, called the Sport Solo, which included narrower gas tanks and 18-inch wheels. The package also included shorter handlebars that were more like the bars on modern bikes and less like the wheelbarrow-like bars on earlier motorcycles. Many two-cammers came with this package, and the package was also available for the standard V-twins. The 74-inch JDH cylinders are identifiable by continuous fins around the exhaust valve area, which increased cooling. Some time earlier, the company had started to make optional colors available, another bow to the needs of sport riders. Although these optional colors were not advertised to the general public, dealer circulars and paint chip sets that have surfaced show that the optional 1928 colors included cream, white, coach green, azure blue, police blue and maroon.
A JDH was not cheap. The sticker price of $335 in 1928 dollars increased to $370 in 1929. At the time, $385 would buy a bare-bones Model A Ford. A tuned JDH could not run on the low-octane fuel available at most pumps, however, so owners who increased the compression ratio and horsepower had to buy or concoct expensive high-octane fuel mixtures.
All Harley Big Twins, including the two-cammers, received three important updates in 1928: a new air cleaner, a throttle controlled oil pump and a front brake. Riders had considered front brakes dangerous on the largely unpaved roads of early Twentieth century America. During the 1920s roads had gradually improved, and better roads meant higher speeds were practically possible — a front brake was both safe and necessary.
The 1929 version of the JDH included a lot of one-year-only parts, including a four-tube muffler that many riders disliked because it was too quiet! Other one-year-only items included dual headlights, a bigger Klaxon horn, and an adjustable generator that let the rider turn the amperage up or down.
In late 1929, Harley switched from the inlet-over-exhaust valve configuration to sidevalve V-twins. These sidevalve engines were heavier than the JDs, and JDs often beat the newer bikes in races during the 1930s. However, the sidevalve engines were more reliable and needed less maintenance.
Harley has never provided production figures for the two-cammers. The only sales figures available lump the JH and JDH with JD V-twin production. Harley sold a lot of JDs in both 1928 and 1929, but most of these were probably single-cam machines. JDHs don’t turn up for sale very often. Pre-1931 Harley-Davidson restoration specialist Steve Thielicke says many JDHs and JHs he sees have welded cases from being ridden past redline too often.
Steve is the owner of Preston Cycle Works in Preston, Washington. He first fell in love with vintage bikes at age 19, and acquired five JDHs “before they were worth anything,” he says. He eventually sold them off for a pile of Henderson parts. Steve’s father-in-law was a hill climber back in the day, and he stoked Steve’s lust for old bikes with stories of crazy biker stunts back in the day, with motorcycles that would now be worth a fortune. “I have a compilation of films of bike events from this area,” Steve says. “People are doing all sorts of things, having fun. We hold these bikes up on a pedestal, but at the time, they were just vehicles.”
One night, Steve was flipping through Hemmings Motor News when he saw an ad for two JDHs at a more than reasonable price. Thinking it had to be a joke, he let it go. Shortly afterwards, he ran into the guy who bought the bikes — which actually turned out to be seven disassembled bikes. “It turned out to be the real deal,” Steve says. The buyer and Steve came to an agreement, and he ended up with all seven basket cases.
Restorers expect basket cases to be missing hard-to-find parts, but amazingly, the two JDHs had all their sheet metal (the hardest to find item) in restorable shape, and almost all other parts present. Steve, like many old bike enthusiasts, has a stash of parts, and was happy to find that almost all the needed missing pieces were in his parts collection, except the exhaust. “Of the JDHs, this one was spectacular. The other had been blown up, and the cases welded. I used the best parts for this bike,” Steve says. Steve does his own sheet metal, his own painting and his own machine work. He sends out parts to be plated, but not before doing the prep work himself. The major challenge was replicating the exhaust — the 1929 four-pipe exhaust has a lot of separate pieces. “It took me two weeks just to make the exhaust.”
Having most of the components is especially important for a 1929 JDH, as finding missing pieces is often impossible. “There are so many one-year-only parts on this bike,” Steve says. “Figuring out what is correct can be difficult. There is some, but not much literature. Sometimes, the correct parts are not in the catalog. They would make changes over a model year and not note the changes,” he says.
Another hurdle is figuring out the correct finish for a particular part. Should it be nickel-plated, painted or Parkerized? Parkerization, a metal preservative finish used on many small parts, may have turned out differently in the 1920s due to the different chemicals available. “I have come up with my own Parkerizing solution, but even so, the hue on new metal is not the same as the color on old metal that has been cleaned,” Steve says. “The hue does not take uniformly, no matter what you do.”
Steve says the JDH is easy to start and fun to ride, and with careful blueprinting and internal polishing, Steve thinks this machine may be able to reach the fabled “ton.” American Iron Magazine publisher and vintage bike fan Buzz Kanter rode a JDH in the 2012 Cannonball coast to coast endurance run, and kept it running for most of the almost 4,000 mile event (he had to have it trucked for one day of the event because of water in the tank). In published interviews, he agrees with Steve’s assessment of the JDH as a fast, easy-to-ride bike.
These days, the bike belongs to vintage car and bike collector Don Hart. “The JDH is a part of the Harley saga,” Don says. “It’s a piece of the puzzle, and there aren’t a lot of them around.” The stuff of legends, indeed. MC