From the October 1940 Issue of Motorcyclist Magazine
Harley-Davidson has announced a 74 cu. in. o.h.v. model for 1941, of which a limited number will be produced. With a bore of 3-7/16” and a stroke of 3-31/32” this new job is intended to furnish all the advantages of the 61 cu. in. o.h.v. but has added power sufficient to handle a sidecar easily, and “a solo motorcycle with performance far beyond ordinary requirements.” Connection rods on the 61” and 74” are identical.
Left side view of the new 74 cu. in. o.h.v. Harley-Davidson announced for ‘41
Among the basic changes and improvements for ‘41 is a centrifugally-controlled oil pump which is to be a feature of all models. The centrifugally-controlled bypass valve regulates the flow of oil to the motor according to the speed of the engine. At high speeds more oil flows into the motor. At low speeds oil is diverted in larger quantities to the gear case and back to the supply tank with less oil passing into the motor. This is a guard against fouled plugs and excessive carbon formation which might result from over-oiling at slower speeds. The vane type pumps of the 45, 74 and 80 side valve motors, and the gear-driven pumps of the 61 and 74 o.h.v. motors incorporate the centrifugally controlled by-pass valve.
A new design clutch goes on the 61, 74 and 80 side valve twins. The clutch assembly has three steel discs, three friction discs and one spring disc. In addition to the three fibre or friction discs, the spring disc also has a fibre facing, giving the clutch the benefit of an additional frictional surface. There are a total of seven frictional surfaces as compared to five in 1940. The frictional area is 121 square inches, 48 square inches greater than previously, or an increase of 65%.
To overcome sticking and grabbing, milled splines in the key ring are eliminated and six hardened-steel keys riveted to the key ring are substituted. Ten driving pins on the clutch hub now take the place of splines on the hub. The three steel discs are driven by the keys in the clutch key ring, and the fibre or friction discs drive through the driving pins on the clutch hubs. Looseness and resulting rattle in the clutch plates are compensated and obviated by two spring-loaded balls on each steel disc.
The clutch hub is new, larger, and has 36 ball bearings arranged in two staggered rows, still further assuring smooth clutch operation. Each of these balls is 7/32” in diameter and each is individually retained. The staggering of these rows gives the effect of four rows of balls. By contrast, the 1940 clutch hub had two straight rows of ball bearings, with smaller balls 3/16” in diameter and were not individually retained.
As the rider sees the new dial and the other assemblies atop the tank of the ‘41 Harley-Da
The clutch for the 45 has also been redesigned, though it is proportionately smaller. It has two fibre discs and one spring disc. It also has six frictional surfaces, including the backer friction disc and a frictional surface on one side of the spring disc. The fibre discs for 1941 are mounted to steel discs the same as in the Big Twins. The new design enables the working parts of the clutch to travel back and forth from a released position to an engaged position more freely. The spring load required to operate the new 45 clutch is approximately 300 pounds, as compared to a spring load of about 500 pounds on the 1940.
The hub of the new 45 clutch is larger than its predecessors, has two staggered rows of 36 steel balls, each ball 7/32” in diameter and each individually retained. The hub is fitted to the main shaft by means of splines. Formerly it was fitted to the main shaft by means of a taper and a key.
Transmission gears on the 45 and Servi-Cars have been strengthened and their diameters increased. Dog clutches are heavier and their diameters increased. Gears are slightly farther apart for easier adjustment. Easier shifting is accomplished thru a redesign of transmission cam and shifter lever gear. The ratio of the shifter lever gear is increased and the track of the shifter cam lengthened.