New 1937 Design In Harley-Davidson Motorcycles

By Chet Billings, Photography by Unknown

In the 61, 74 and 80 models, both tanks carry gasoline, the left compartment having a capacity of two gallons and the right having two gallons in the 74 and 80 models, while the 61 holds one and three-quarter gallons. The 45 carries three and three-eighths in the left tank and the right tank one and one-eighth gallons of oil. All tanks are fitted with a two-way shut-off cock that feeds in one position until about a half-gallon remains and in another position permits use of the reserve. Filler caps operate with a half turn.

The speedometer is driven by spiral gears in the gear box in 61, 74 and 80 twins. The driving mechanism is in a constant bath of oil. On the 45 driving is accomplished by spiral gears enclosed in rear wheel brake side plate. On all models the driving cable passes up between the tanks, out of sight.

A constant mesh design transmission with self-locking shifting clutches is used on the 61, 74 and 80, featuring four speeds forward. Fourth operates through direct drive. The 61 o.h.v. clutch is now to be used in the 74 and 80 models. Clutch adjustment screws are accessible through removal of the clutch releasing disk. A three-speed transmission with reverse speed can be obtained on all models at additional cost.

Front forks are tubular chrome-molybdenum as used on the 61 and these will appear on the 74 and 80 models. It is a rigid light weight fork.

There are a number of improvements in the 74 and 80 motors. Roller bearings replace the former bronze bearing on the pinion gear shaft main bearing. With similar roller bearings on the sprocket shaft side, the motor-flywheel assembly is 100% roller bearing throughout. Friction is reduced and fitting of new bearings is facilitated whenever that should become necessary.

The crankpin has been increased one-eighth inch in diameter being thus now one and one-eighth inches. Bearing surface is increased and motor life is increased at this point. The outside diameter of the flywheels is from eight inches to eight and nine thirty-seconds inches. Connecting rods have a bigger end to accommodate the new crankpin. Timing gears, cam lobes and shafts are now of integral construction instead of assembled units.

On the 74, bore is now three and five-sixteenth inches and stroke four and nine-thirty-seconds as compared with the former three and seven-six-teenths bore and four-inch stroke. Displacement is 73.576 cubic inches. Bore on the 80 motors is three and seven-sixteenths with a stroke of four and nine-thirty-seconds with a displacement of 78.75 cubic inches.

Flywheel counter weighs have been changed to correct vibration at high speeds.

On the 45 motors a roller bearing replaces the former bronze bearing with roller bearings on the sprocket shaft and on the lower connecting rod big end. Cam gears are made in one piece similar to those on the 74 and 80 motors. Crankcase and gear case, and gear case cover present a new racy appearance with cooling fins which facilitate cooling and strengthen these parts.

The timer on all models is now mounted in an upright position on the gear case cover and is driven by spiral gears. The new timer and mounting offers better cooling and more accurate maintenance of spark timing. Circuit breaker points and condenser are easily accessible for adjustment or replacement. The cover is chromed.

Improvements on the 61 o.h.v. include a positive stop shifter gate, shifter lever is flat instead of tubular, to fit shifter gate stops. The brake has been made larger in diameter and in width, being now the same size as the 74 and 80 models.

The clutch release pedal on 61, 74 and 80 models has been fitted with balancing springs. Clutch is held positively in “in” or “out” position, the pedal working with natural foot action.

Wheels on all models are 18-inch, 18x4.00 balloon tires, giving for low position.

By Chet Billings
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