53 Arthur and Bill’s second engine dwarfed the first, and performed satisfactorily in The Motor Company’s first machines. It displaced 24.74 ci by using a 3-inch bore and 3-1/2-inch stroke, and hefty 8-inch flywheels. The additional 1 horsepower (approximately) gained from the new engine allowed the motorcycle to achieve speeds up to around 35 mph. Milwaukee’s hills were no longer of any concern.
54 While not a “clutch” in the technical sense, Harley-Davidson motorcycles began using a spring-loaded belt tensioner in 1906. A lever mounted to the left side of the gas tank controlled the tensioner. It allowed the rider to place enough tension on the drive belt so that the engine couldn’t overcome the resistance. The engine continued to run, but the belt remained stationary, as did the rear wheel. When the rider wanted to go again, he simply pushed the lever forward and the bike started to move. The system was far from perfect, and had trouble working if it was wet or greasy, but it laid the groundwork for what became the modern clutch. An increased displacement of 26.8 ci on the 1907 single brought the horsepower count to 4; the Harley-Davidson could now achieve 45 mph.
55 Harley-Davidson produced its first prototype V-twin engine as early as 1907, although the first public appearance of a V-twin was in 1908. It used the same de Dion design as the single, but it was fitted with a beefed-up bottom end. This intake over exhaust (IOE) engine displaced 49 ci (810 cc) and made about 7 hp. Despite its 65-mph top speed, The Motor Company’s first V-twin had a few drawbacks in addition to its hefty price tag. It didn’t come with a chain tensioner as the singles did, making it difficult for city use and requiring riders to have to pedal-start a large-displacement engine every time they had to start going again. This might not have been such a big deal except that starting the thing was a pain unto itself. The engines still used an atmospheric valve system that used cylinder vacuum to actuate the valve, which was made difficult by the V-twin’s high crankcase pressure. This engine was used in a production model for the first time in 1909, but was dropped for 1910; it was not considered a viable option until 1911 when mechanical valves were introduced.
56 Most customers opted for the single-cylinder motorcycle in 1909, which, in addition to chassis upgrades, saw numerous improvements to the drivetrain and controls. A quick glance at a 1909 model reveals a lack of the usual linkages, chains, and levers that adorned strap tank models. Now, the throttle control and spark advance grips used cables that ran through the handlebar. The 1909 twin lacked a chain tensioner; the single used an improved tensioner with a spring-loaded thumb release and a notched gate on the gas tank for solid engagement. The tensioner pulley was moved closer to the engine pulley to put more pressure on the belt, ensuring more effective clutching. The Model 5’s single-cylinder was bored up to 3.31 inches to displace 30.16 ci, which made it good for 4.3 hp.
57 Other than the 6E racer, Harley-Davidson didn’t offer any twins for sale. The thinking must have been to take the year and perfect it before bringing it back to the public, an approach that is typical of The Motor Company to this day. So, in 1911, they reintroduced the Model 7D V-twin to the motoring public. Displacement remained at 49 ci, which was all that was necessary to propel the 6-1/2-hp 295-pound machine to 60 mph. Although it was a superior engine, compared to the offering from two years earlier, it wasn’t all that special when compared to the competition. With a $300 price tag, motorcyclists of the day could opt for a competitor’s machine, which made more power for less money. And four-cylinder motorcycles had also begun to make their powerful presence known.
The overall shape and design of the Harley-Davidson V-twin has remained relatively unchanged through the years from the first 45-degree engine with Y-shaped manifold and carburetor in between the cylinders. In 1912, the magneto was moved to behind the rear cylinder. However, the gearcase on this original 1911 resembles that of a modern Sportster more closely, except that the oil filter would be where this magneto is located.
58 Starting the 7D engine was made easier thanks to mechanical intake valves; they required an additional pushrod on each cylinder. The dual pushrod design on a brand-new Harley began back in 1911 and, even though it has changed considerably since then, all air-cooled and Twin-Cooled (air and oil cooling) Harley-Davidsons still have a pair of parallel pushrods on the right side of each cylinder.
59 Up until 1910, Harley-Davidson engines had horizontal fins from the bottom of the cylinder all the way up to the spark plug. To many folks, this makes the cylinders look like a beehive, leading collectors and restorers to call pre-1911 engines “beehives.” These single-direction fins did a good enough job when engines were only making a few horsepower, but as power increased, so did heat. For 1911, the fins on the top of the cylinder, from just below the intake manifold and up, became vertical. This allowed for more fins, and better cooling, at the top of the cylinder where combustion occurred. Vertical fins are found on all 1911 and later F-head cylinders, as well has Flathead and K-model cylinder heads.
60 The competition’s advantage in the engine department didn’t last long. Harley-Davidson unleashed a new, more powerful V-twin engine option and wholly modern drivetrain on the public in 1912. With a 3-1/2-inch bore and 3.31-inch stroke, the Model X8E undersquare engine displaced 60.32 ci, almost 1,000 cc. The 8 hp produced by the larger twin could bring the motorcycle up to 65 mph.
61 In addition to the honkin’ new twin engine, the new Model X8E had two other drivetrain features that combined to make it one of the best motorcycles that money could buy in 1912. The X designation meant that the bike had a real mechanical clutch, dubbed Free Wheel Control by its inventors Bill Harley and his old buddy Henry Melk, who had the lathe down the street. Clutches were available for an extra $10 on the twins, which included the 8-hp version instead of the 6-1/2-hp version.
The Free Wheel Control clutch built into the rear hub in 1912 added a whole new dimension to the viability of the motorcycle as a machine for everyday transportation. After it was started, a rider simply operated a lever to engage and disengage power to the rear wheel, allowing the motorcycle to sit at idle and not have to be pedaled (and therefore restarted) away from every stop. Although chains were first used on twins in 1912, singles, such as this one, didn’t have a chain-drive option until 1913.
62 The top dog Model X8E took performance a step further by using the first chain-drive system to drive the rear wheel. Actually, it used two chains. The engine transfers power to a primary chain, which spins a set of gears that operate the final drive chain, which fits around a gear on the rear wheel hub. This was a first, as was the first use of the traditional primary chain cover. A slotted gear on the left side of the crankshaft oiled the primary chain as well as the drive chain. Represented by the E designation, both twin options could be ordered with a chain or a belt, while singles weren’t offered with a chain until 1913.
The defining look of the left side of a Harley-Davidson came to fruition in 1912 with the first appearance of a chain-driven rear wheel. The belt drive connected the engine pulley directly to the rear wheel. However, the chain-drive used a series of sprockets at the engine and the pedals, and at the rear wheel. Look at any new Big Twin and you’ll see that it uses the exact same pattern, albeit with a belt instead of a chain.
63 The 1913 Harley-Davidson Model 9A was the only motorcycle in the United States still available with a belt drive and was the last Harley available with a leather belt drive. This is actually pretty surprising, even for Harley-Davidson; not only had the new V-twins outsold singles in 1912, but the single-cylinder engine was now larger and produced even more power. This time, the size grew by increasing the stroke from