1924 Harley-Davidson JDCA
With an experienced team and a lot of data.
Harley-Davidson had introduced its first ever V-twin in 1909, but it wasn’t until 1911 when they added a mechanical inlet valve (the so-called overhead “pocket valve”) that the company got it just right. A 61 cubic-inch version of the engine would remain in production for two decades. By 1914 Harley’s V-twin featured chain final drive, a proper clutch and a three-speed gearbox. A kick-starter came shortly after.
A 74 cubic-inch model called the JD was introduced for 1922. The 22JD came with full electrical equipment, while the 22FD model was fitted with a magneto. Both had an inlet-over-exhaust V-twin engine, a Schebler carburetor, three-speed hand-shift transmission, single bucket saddle, sprung front forks, hard-tail rear, luggage rack, kickstand, and a foot-operated rear drum brake. The wheelbase was 59.5 inches.
The JD could achieve up to 40-60 mpg, and the sidecar model had a plate that fitted below the cylinder to lower compression and increase engine life. The big twin was built in response to the four-cylinder Henderson, which was smoother but not as reliable. It had sprung front forks, but a hard-tail rear end, which prolonged chain life.
The JD’s lighting and ignition consisted of 6-volt generator/ignition unit storage battery, headlight, taillight and motor driven oil pressure light. The ignition system involved a circuit breaker, distributor and high-tension coil and was located behind the engine, away from rain.
Paint was the typical olive drab with attractive pin striping over the dual fuel tanks and oil tank. The front and rear lights were optional and and rubber footboards were fitted along with a rear luggage rack and stand. There was nickel plating throughout, and the rims were painted over stainless steel spokes.
Two important changes for the Harley-Davidson JD came about for 1924. Alemite lubrication was introduced on all bearing surfaces except those inside the engine, and a factory grease gun could force lubricant in at 500 psi. The frame was also dropped, which resulted in a lower riding position.
Aluminum pistons were fitted as well. They weighed less and produced more power, and were much less likely to seize. 1926 saw a teardrop gas tank and balloon tires, while throttle-regulated oil pressure and a front brake followed in 1928.
The JD models proved both fast and reliable and were raced worldwide with great success throughout the 1920s. A JD sidecar outfit driven by Clark and Webster set a Sydney to Perth record in Australia in 1924 and that same year Walter Patterson rode 170 miles from Tacoma, Washington to Portland, Oregon in a little under six hours “no hands”. The bars were removed and his wrists chained to the tank.