Missing Link: 1919 Harley-Davidson Model W Sport

Harley-Davidson’s first sidevalve engine was also its first horizontal flat-twin engine.

| May/June 2018

1919 H-D Model W Sport
Engine: 35.64ci (584cc) air-cooled sidevalve horizontally opposed twin w/cylinders in line w/frame, 2-3/4in x 3in (69.9mm x 76.2mm) bore and stroke, 3.75:1 compression ratio (est.), 6hp (factory claimed)
Top speed: 50mph
Carburetion: Single 3/4in (19mm) Schebler
Transmission: 3-speed handshift, chain final drive
Electrics: Magneto ignition
Frame/wheelbase: Single downtube keystone-style w/engine as stressed member/57in (1,448mm)
Suspension: Trailing link w/single spring front, rigid rear
Brakes: 7in (178mm) external contracting drum rear
Tires: 3in x 26in front and rear (3in x 20in modern equivalent)
Weight (wet): 250lb (114kg)
Seat height: 29.5in (749mm)
Fuel capacity: 3gal (13.6ltr)
Price then/now: $355/$25,000-$45,000

During most of its long existence, Harley-Davidson has built its reputation more on making powerful, reliable and sturdy V-twin-powered motorcycles than on innovation. Yet in 1919, Harley introduced an entirely new engine with essential features that wouldn't become part of the family lineup for almost another decade.

By the end of 1918 and with World War I over, the Harley-Davidson company looked forward to peace, prosperity, and selling motorcycles — especially to veterans who had been introduced to motorcycles while in the military. Company engineer William Harley thought these new riders would want an innovative, user-friendly motorcycle with updated features, and he headed for the drawing board to deliver.

The bike that H-D introduced to dealers in mid-1919 was definitely innovative. Advertised as the Harley Sport, the Model W was the first Harley with a sidevalve top end, which was state of the art at the time. Before 1919, all Harley-Davidson engines featured the intake-over-exhaust valve configuration used on most motorcycle engines since the 1890s. Running without valve seals, inlet-over-exhaust engines routinely blew oil mist all over the rider's pants. Competitor Indian was proving that sidevalve engines were not only quieter and cleaner, but also powerful, reliable and fast, and Indian's sidevalve motorcycles regularly won both speed contests and endurance races. It seemed reasonable for Harley to experiment with a setup that had been proven by other companies.

Harley's flat twin

The engine William Harley conceived was unlike any previously built by Harley-Davidson. Unlike Indian's V-twins, Harley's new engine was a flat twin. Except unlike the now-familiar BMW with its cylinders sticking out to either side, the cylinders on Harley's new sidevalve were in line with the frame, one forward of the crankcase and one aft. Interestingly, this cylinder arrangement, chosen to minimize vibration, was used by Indian on the 1917-1919 Model O, which was taken out of production the same year Harley introduced its own flat twin. A single casting combined the intake from the carburetor and the exhaust to the muffler. Advertising literature of the time claimed that heating the intake charge helped atomize the fuel for combustion. Given the poor quality gasoline that was generally available, it probably did.

One camshaft operated both the intake and exhaust valves. The engine and gearbox for the 3-speed transmission were housed in the same set of castings, split vertically. A "bacon slicer" outside flywheel was covered by a pressed steel cover. Oil was circulated by a plunger pump, and rear drive was by an enclosed chain.

6/21/2018 11:44:37 AM

While I have probably met Thom at Vallejo HD, I would like to know if he will ever show his rare collection.A.WILLIAMS, Parma,ID.

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