Cars & Vehicles Motorcycles

Harley-Davidson Sport Twin

The recent release of Harley-Davidson's all-new, water-cooled V-twin, the Street 500 and 750 machines, got me thinking about all the other motor configurations Harley has experimented with through the years that were radical departures for their day. Still, they made it into production and hung in there amid an onslaught of criticism and derision.

Not so very long ago, The Motor Company introduced a very different motorcycle: the water-cooled V-Rod, which represented a whole new take on motorcycles for the traditional Harley-Davidson marque. The V-Rod represented real, out-of-the-box thinking, and I was encouraged that H-D had the gumption and commitment to come up with this new machine and bring it to the market. Of course, if we look back even further, say to the late teens of the last century, we see in the history of The Motor Company another truly radical machine in the form of the 1919-23 Sport Twin, which was unlike any other motorcycle in the lineup at the time. This horizontally opposed flat twin (meaning the cylinders were laid out on a flat plane with one facing forward and one facing rear) was devised as a direct competitor to the Indian Model O, with both companies vying for a share of the smaller displacement motorcycle market, both here and abroad.

The Sport Twin had many engineering firsts: it used a flat head, or a side valve design, as opposed to the traditional inlet-over exhaust (IOE) setup of the period. This new head and valve design was simpler, used fewer parts, was more reliable, and would hold an important place in the product lineup. It was used on many H-D models from VLs to ULs to 45s and Servi-Cars. It played a large role in bringing reliability and longevity to engine manufacturing.

The Sport Twin also used a unit construction layout, with motor transmission incorporated into a single crankcase much like the modern Sporster. The frame continued the innovation with the motor/tranny being a stressed member of the frame structure, like some factory racing machines of the period (think ducati superbike today). The external flywheel has never been seen before on a Harley; it was always buried deep inside the cases.

Visually, the engine package is reminiscent of a Moto Guzzi from the 1940s. The front fork is a trailing link arrangement with a somewhat leaf spring style incorporated; this is different from both the Harley springer and Indian left spring front ends of the day. A fully enclosed chain drive was also a first, and keeping dirt, mud, and road grime off the chain is always a great idea. The gas and oil tank was enclosed in the confines of the frame, another unique approach for Harley.

The engine placement meant a low center of gravity and easy riding characteristics. The opposed cylinder layout meant the cancellation of vibration and resulted in a very smooth running engine. I can attest to their no-vibration idle and quiet-running motor, having heard a few run at AMCA meets throughout the years. Weighing in at just under 260 pounds, the bike was the perfect mount for smaller riders and popular with women.

Marketed as a 37€machine (the factory always rounded up on cubic inches), these 35.64€ (584cc) motors, with a bore and stroke of 2.75 mm x 3.00 mm, put out about 6-7 hp. The Sport Twin transferred power through its three-speed, hand-shifted transmission and used a final chain drive to turn the rear wheel. Top speed was in mid-50s and pricing varied by model, but started at $335 and climbed to a high of $395 by the end of the run.

Always in search of notoriety to promote its machines, H-D publicity manager Hap Scherer set endurance records in a three-flag run from British Columbia to Tijuana as well as a New You to Chicago run, proving the Sport Twin's reliability and rugged construction - Jim Babchak

Leave a reply