World War I, Harleys used German-made Bosch magnetos. As you’d expect, that became a slight problem after the war; The Motor Company switched to magnetos made by Dixie and other American manufacturers until the magneto became obsolete. In 1917, H-D gave its street V-twin the powerful four-lobe cam that it used in the eight-valve racers. That, along with timing and lift adjustments allowed the 17J to make 16 hp.
178 The popularity of sidecars continued to grow, and Harley-Davidson improved the hack ownership experience by recommending a 14-tooth countershaft sprocket with a higher gear ratio. Naturally, top speed decreased, but ridability at regular speed ranges improved. For the owner who also liked to ride solo, the 14-tooth sprocket worked fine. Both regular and sidecar gearing were available.
179 Indian introduced the 350-cc Prince model in 1925; Harley-Davidson responded quickly and powerfully with a pair of 350-cc singles for the consumer and for the racetrack. The 1926 Model A was the first sidevalve engine produced since H-D dropped the horizontally opposed W. At 344 cc (21 ci), it used a vertical cylinder like the older pocket-valve single, except that this one had a flat removable combustion chamber that housed the spark plug, similar to the W. It produced about 8 hp and was available with a magneto (AA) or a battery (AB).
180 As part of the response to the Indian Prince, Harley-Davidson also released an overhead valve (OHV) version of the Model A, dubbed the Model B, which marked the first time that an OHV Harley-Davidson was sold to the public. Many people mistakenly give the 1936 Knucklehead that glory. Designated as the BA (magneto) or BB (battery), the OHV single produced 12 hp; racers and sporting riders purchased most of them. Compared to the side-valve, of which 4,000 were built, only 722 OHVs were produced.
181 The W Sport Twin, produced from 1919 to 1923, was Harley-Davidson’s first attempt at selling a horizontally opposed twin. It pioneered engineering technology that wasn’t seen for another decade at The Motor Company; it didn’t release another Flathead twin until the 1929 D. The 36-ci 6-hp W uses a sidevalve, or Flathead, engine design that eliminates all moving parts from the cylinder head and rocker arms. Fewer parts make it more durable and run cooler. The construction of the engine differs from what we usually picture, which is the BMW design. The cylinders go front to back; that is, the front cylinder points toward the front wheel and the rear cylinder points toward the rear wheel. This kept the package narrow and well-balanced, but it did remove the cooling advantage associated with perpendicular opposed twins.
The intake and exhaust manifold on the model W Sport Twin looks more like something that you’d find on a GM small-block than on a Harley-Davidson! In addition to the completely awkward design, the hot exhaust pipes run alongside what should be a cool air intake tract.
182 Another first for Harley-Davidson is the Sport Twin’s unit construction. This means that the transmission is actually inside the engine case, as it is on a modern Sportster. This efficient design wasn’t seen again in a Harley twin until the 1952 K model. It was also the first to use an air cleaner to keep particles out of the carburetor. The 19W is the only H-D known to use an external flywheel (covered by a metal shroud) and the first to use a fully enclosed drive chain. The overall design eliminated several key areas known for oil seepage, making the W a very clean motorcycle to own and ride.
183 Harley-Davidson introduced its first 74-ci engine in the JD (battery) and FD (magneto) models for the 1921 lineup to compete with the power of the 4-cylinder models available from other manufacturers. The company actually looked into building a 4-cylinder version, but increasing the Big Twin’s displacement made more sense. The new 74-ci V-twin sported a 3.42-inch bore with a 4-inch stroke to produce 18 hp. The 74-ci engine went on to be one of the most common for Big Twins until 1978.
184 Both the OHV and the sidevalve singles used newly designed removable heads developed by British engineer Harry Ricardo. Ricardo discovered that more turbulence in the combustion chamber allowed the air and fuel to mix better, thereby creating better combustion, which not only provided more power but better fuel economy and a cleaner engine. Ricardo achieved this greater turbulence by offsetting the cylinder head so that the head is within 1 mm away at top dead center (TDC) over part of the piston. This “squish band” shoots the air/fuel mixture into the larger combustion chamber at an intense speed, sending the mixture into a turbulent frenzy.
185 In 1929, The Motor Company introduced its zany four-muffler exhaust system on all twins. This particular exhaust system, which was used only in 1929, used a dual, side-exiting design that piggybacked one muffler on top of the other on either side. The entire system was quiet but heavy. In 1930, it decided to drop the left-side mufflers in favor of a pair of mufflers on the right. By 1931, a single, albeit larger, muffler was used, which was fed by both cylinders.
186 Harley-Davidson introduced the model JDH (74 ci) and JH (61 ci) in 1928 essentially as race-ready street bikes. The engine was a two-cam design based on what the H-D factory team campaigned to great success throughout the 1920s. They used F-head pocket-valve cylinders that housed Dow metal pistons, which were manufactured using magnesium alloy. With a price tag of $370, the JDH was the first Harley street bike capable of achieving 100 mph. The Two-Cam engines are immediately recognizable by the kidney-shaped cam cover that comes up in the back to cover the magneto. It is one of the most collectable Harley-Davidsons today; examples have sold for more than $100,000 at auction.
187 Even though the recirculating oil system was still nearly a decade away, The Motor Company realized that most riders didn’t want to have to keep up with oiling their machines differently at different engine loads and throttle settings. The engineers came up with a way to automatically adjust oiling based on throttle position. They ran a cable to the oil pump, which then operates off the throttle linkage on the carburetor. More oil flows through the pump on the cam cover as the throttle is opened wider. An additional hand pump on the oil tank was still used for excessive uphill or sidecar loads. This system was in place until 1937, when all Flatheads were converted to recirculating oil.
188 Sure, Harleys are a great way to travel, but some times even the narrowest of motorcycles can’t sneak through a traffic jam. So why don’t you take to the air? In 1927, a do-it-yourself kit available through Popular Mechanics included an adapter that mounted to the primary sprocket shaft of a JD engine to which a builder then attached an airplane propeller and used that setup to power a homemade aircraft.
189 Another interesting propeller-driven variant is the ice glider kit available through the Mead Glider company. Unlike the aircraft propeller, the Mead kit ran a chain off the stock primary sprocket to turn the propeller, which was placed on the ice glider’s chassis toward the top of the cylinder heads. The company advertised its kit to Harley-Davidson owners with the recommendation that they could build the ice glider easily. Then, during the winter, transfer their motorcycle engine into it.
190 When initially purchasing a motorcycle in the 1910s, it was important to mention whether or not it was for sidecar use. H-Ds meant for solo use arrived from the factory with a 15-tooth engine sprocket, which was well matched for the weight and acceleration versus top-speed needs. A sidecar rig with that gearing accelerated at a much slower rate while also putting too much pressure on the clutch, especially on hills. In addition, the added weight and running gear couldn’t propel the machine to top speeds. Therefore, a 14-tooth engine sprocket was offered for sidecar customers so they could get the most out of the heavier machine.
191 In 1924, Harley-Davidson hired Ace’s chief engineer, Everett DeLong, on a six-month contract to develop a 4-cylinder engine for The Motor Company. Ace had been successful with this type of engine for many years. Initially, he worked one of his inline-4 Ace designs into a JD chassis, but the production version would have required too much expensive tooling at the factory. His next prototype engine wouldn’t have added much to the budget. He mounted two JD V-twins side by side, connected at the crankcase. The displacement of both engines would
