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 3-1/2 to 4 inches. Displacing 34.47 ci and pushing 4-1/2 hp, the Model 9 earned the nickname “5-35” for its approximate power and displacement figures. The single-cylinder 5-35, which was produced until 1918, could hit 50 mph. The 9A and 9B (both chain-drive) were available standard with the rear hub clutch and both retailed for $290. Also for 1913, The Motor Company began the practice of balancing the flywheel, rod, and piston as a single assembly, which made the engine longer lasting and smoother to operate.
64 The 1914 Model 10-F is the only model to feature H-D’s first transmission. Patented by William S. Harley, it features two speeds located in the rear hub. It added yet another dose of rider friendliness to the early machines. At least, that was the idea. The bicycle-style epicyclical rear hub was so revolutionary, and had such tight tolerances, that many riders found it difficult to operate. A company service bulletin was published that reminded 10F owners not to force the shifter into gear when the machine wasn’t running, which could cause the shift lever to bend. The 10-F also saw the first use of floorboards and a pedal-operated drum brake in the rear.
65 The Harley-Davidson motorcycle took a major stride forward with the 1915 11-F and the introduction of the 3-speed, sliding-gear transmission that sits behind the engine. The new 3-speed featured large ball bearings to secure the main shaft; two special, heavy-duty roller bearings allow the jackshaft to spin smoothly. The jackshaft transmits power in low and intermediate gear while the transmission is essentially free running in high gear. For extra durability, the engineers made sure not to include any small parts that could potentially break or wear out, and the 3-speed proved to be extremely reliable. The transmission is controlled with a foot-operated rocker clutch and a gated shift arm on the tank. With 9,855 produced, 3-speed H-Ds made up 75 percent of that year’s total motorcycle production. The 1915 11-F is, like the 10-F before it, a one-year-only design thanks to its using bicycle-style pedals to start the engine.
The Motor Company’s 1915 model 11-F set the stage for every Big Twin to follow with its durable 3-speed transmission, a powerful V-twin, and an automatic oil pump, which is visible on the gearcase. By using a separate engine and transmission, linked only by the primary chain, this setup would last for another 80 years on some Big Twin models.
66 In addition to the new 3-speed transmission, Harley-Davidson completely redesigned its 61-ci IOE engine for 1915. It now used larger intake valves that now entered the heads at a 45-degree angle instead of a 60-degree angle. The engine used new cylinders and a larger intake manifold to increase airflow. To handle the power increase, engineers used heavier flywheels with a 1-inch crankpin (previously 7/8 inch). The new Harley-Davidson–made bearings are 3/8 inch wider than on the previous engine. A newly designed, more efficient muffler was used and, while it produced significantly less backpressure, it also made less noise.
67 The engine lubrication system was also completely reimagined in 1915, beginning with the oil tank’s relocation from underneath the seat to the left side of the gas tank; it now displaced 2-1/2 quarts. A new, automatic oil pump, visible on the cam cover on the right side of the engine, ensured precise lubrication at any speed and crank pressure. Occasionally, when running flat out, or powering up a steep incline, the rider had to pump in extra oil via the auxiliary hand pump that sat atop the oil tank.
68 Harley-Davidson claimed exactly 29 engine improvements, leading the 1915 models to put out an advertised 31 percent more power at 2,500 rpm and a whopping 47 percent more power at 3,000 rpm. The Motor Company guaranteed that the 11-F was capable of achieving 65 mph. My friend and colleague, Cris Sommer Simmons, can vouch for that claim; she rides her 1915 11-F regularly (and rode it more than 3,000 miles on the 2010 Motorcycle Cannonball).
69 In 1915, The Motor Company guaranteed the 61-ci V-twin to produce 11 hp. Solid output on these early machines, no doubt, but just because the company guaranteed it, didn’t make it so. In fact, in typical Harley fashion, 11 hp was a modest figure, and many of its street engines actually produced up to 16 hp on the dynamometer thanks to larger intake and exhaust ports, which lead to larger valves and carburetors.
70 With the sliding-gear transmission in 1915 also came the first use of the gated shift lever on the left side of the gas tank. The gate is labeled with the different gear positions so the rider can easily and confidently put his motorcycle into the correct gear. The 1915 gate is mounted to the left-side oil and gas caps and is notched to make it more difficult to go back a gear by mistake.
71 Some riders today have trouble stopping and starting on a hill. So imagine what it was like for riders in 1915 when they were learning to use a clutch and transmission for the first time, and didn’t
