Horizontal Twin From Harley-Davidson

New Middleweight Sport Model Has Unit Power Plant, Final Gear Short Drive and Enclosed Chain-Numerous Examples of Over Designing

The two-throw crank is an especially neat job, drop forged, of course. The crank pins are 1 3/8 inch diameter and the rods are not split on the lower ends but slip over the cheeks to their proper positions. They are held in place by locking rings. The crank throws are drilled and mounted with counter- weights to neutralize vibration. This is one of the secrets of the velvetiness of running and smoothness over a wide throttle range. This motor will “idle” exceptionally slow without thumping. Big roller bearings on the rod ends insure long life and minimum friction at this heavy duty point.

Rear cylinder cooling has been achieved to complete satisfaction. One of the methods used was slightly less compression in the rear barrel. It is asserted that absolutely no overheating will be experienced.

New Harley-Davidson Sport Model

Taking cognizance of the very poor quality of the average gasoline of today, the builders of the Sport Model have paid attention to easy starting. There’s a unique manifold with a “hot spot” that prevents condensation and assures a quick firing mixture. The manifold is a single casting with twin passages and a “cross-over” from the exhaust to the intake, whereby exhaust heat warms the admission charge. The attachment of the manifold is a particularly clever piece of work.

Probably the closest approach to 100 per cent automatic and efficient lubrication is achieved in this model. A simplified edition of the Harley-Davidson plunger pump circulates the oil to the gears, whence it goes into the crankcase and eventually the spray is exhausted on the drive chain through the breather. The pump stroke, of course, is adjustable. There’s also a hand pump.

Much Clutch in Small Space

Harley-Davidson has scored a distinct triumph in the new clutch. Its a multiple disc type, running in oil. Compactness to the ‘nth degree is apparent and this permits the clutch being tucked away in a very small space. While discs are small in diameter, there are thirteen of them and an 860 pound spring furnishes the grip-some grip. This “little” clutch has 48 square inches of contact surface against 56 inches on the big twin.

The internal helical gear drive from the crankshaft to the main shaft of the transmission is another innovation. These gears are especially husky for the hard work put on them and run quiet as a watch. Meshed with them are the cam action, ignition and oil pump drivers.

Harley-Davidson is the second big maker to carry the short drive through gears and use only one chain in the line. The system has obvious advantages to recommend it. A real chain case, that is quick demountable, and that permits chain adjustment without tearing everything apart, renders this unit especially attractive. It steps up chain drive to its highest efficiency.

In the keystone frame and truss forks with plunger spring shock absorber, Harley-Davidson has made two departures from its previous designs in these units.

The low-slung motor affords a delightful ease of balance and handling in hard going as well as on boulevards. The short-legged man will especially appreciate the low saddle position, 28 1/2”from the ground.

Workmanship, standardization of details and equipment, all qualify to the well-known high standards of Harley-Davidson. Production of the Sport Model for this season will be limited to 20 per cent of the total factory output, and from the dealer enthusiasm manifested at the district conferences, the available supply will be many times oversold.

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