New 1937 Design In Harley-Davidson Motorcycles

From the November 1936 issue of Motorcyclist Magazine

The prelude to any discussion of Harley-Davidson design for 1937 must necessarily start with some mention and explanation of the o.h.v. 61 which was experimentally introduced in 1936.

After long engineering development, 70,000 hours of testing, and studied showings to old experienced riders the 61 was placed upon the market without the usual advertising and sales effort accompanying the introduction of a new model. It was a definite program intended to get owner-reaction and owner-experience. In the total there were approximately 2,000 machines of that model gradually put into service to test new departures in design.

With the results of that campaign as a gauge there are many major changes in all models of Harley-Davidson for 1937, and the items of new design constitute a very favorable testimonial for the fundamental success of the new features in the 61.

There is no doubt that the double loop trussed frame provided handling qualities which met with instant approval. Technically it not only gave strength but established a low saddle position, and dropped the center of gravity of the whole machine. In the new models the frame will be used on the 61, 74 and 80 models. To adapt the frame to the 74 and 80 models larger front frame members have been used-larger in diameter and of thicker gauge steel, each carries a six-inch reinforcement and ties into a drop forging at the bottom providing for sidecar or package truck attachment. The top frame member incorporates an eleven-inch reinforcement between seat post and seat bar connection. Rear stays are made of heavier gauge steel. The transmission mounting bracket is stronger and a hardened steel stabilizer bushing has been put on the seat post mast.

The circulating pressure oiling system as used on the 61 has been extended to all models. A main feed pump mounted on the gear case cover in the 45, 74 and 80 models, and mounted on the crankcase in the 61 o.h.v. model, introduces oil from the supply tank. A vane type pump is used in the 45, 74 and 80 models, driven by the rear exhaust cam gear shaft. The pump in the 61 is gear type, driven from pinion shaft. Oil under pressure is delivered through pinion shaft, flywheel, crankpin to lower connecting rod bearings and all motor surfaces. In the 61 a by-pass from the main feed line carries oil to rocker arms and valves and a positively timed rotary breather valve driven from the cam gear, carries oil and mist in the motor to the gear case basin. A screen is incorporated in the breather valve. A scavenger gear pump on the crankcase returns oil to the tank.

In the 45, 74 and 80 models, oil and mist in the motor are blown through a vertical breather valve, operated from pinion shaft, into the gear compartment. Oil condenses, passes through a cone sieve into the gear pump underneath the gear compartment and is returned to the tank. A vent pipe on all models leads from the tank to the gear compartment.

A one-gallon steel oil tank, around the battery, holds the oil on 61,74 and 80 models, while on the 45 the tank lies parallel to the gas tank and has a capacity of one and one-eighth gallons.

The front chain on all models is lubricated from the motor.

An instrument panel which includes speedometer, ammeter, oil pressure gauge, ignition and light switch, and lock, is used-the same as appeared on the 61. This will appear on all models.

Ignition and light switch are master key locked and when “off” eliminate tampering, it being impossible to even blow the horn.

Welded steel saddle-type tanks of teardrop design are featured on all ‘37 models. These new rigid tanks are three-point mounted to the frame.

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.

Color combinations for 1937 are teak red striped in black and edged in gold, and bronze brown striped in delphine blue and edged in yellow. The outstanding characteristic of the new machines is that one color dominates the motorcycle, bronze brown on one and teak read on the other.

National conditions on materials and in connection with many phases of production are such that delivery is a ticklish problem with any factory. However, the Harley-Davidson factory has anticipated to the extent that even now demonstrators are being displayed by nearly all dealers the country over and each day sees a speeding up of the factory wheels of production.

So see the new ‘37 models and take a ride. You’ll be surprised at the smooth running motors and the nicety of handling. 1937 is seeing a step forward in motorcycling and you’ll want to have a part of it.

The double loop trussed frame, as introduced in the 61 o.h.v. during 1936 is being extended to the 74 and 80 models. The new frame provides low saddle position and a low center of gravity for the whole motorcycle, which makes for ease of handling under all road conditions
A welded steel saddle-type tank such as will be standard on all models. This teardrop design is three point mounted to the frame. In 61, 74 and 80 models, both tanks carry gasoline. In the 45 model the right tank carries oil and the left tank carries gas
The 1937 models of Harley-Davidson, in order from top to bottom-45 Twin, 74 Twin, 80 Twin and 61 o.h.v. Twin. Some of the outstanding features on these models are: circulating pressure oiling system; double loop trussed frame on 61, 74 and 80; built-in instrument panel; welded steel tanks; speedometers driven by spiral gears in the gear box on the 61, 74 and 80; four speeds forward on 61, 74 and 80 with constant mesh design transmission with self-locking shifting clutch; and external ignition timer. The motors are air-cooled, four-stroke cycle twin cylinders, with side by side valves, Ricardo-type removable heads on 45, 74 and 80 Twins. Overhead valves in removable cylinder heads on 61 cu. in. Aluminum alloy, cam-ground, double-slot pistons and mirror-honed cylinders on all models. All main bearings roller bearings. Fully enclosed and lubricated valve gear. Chrome-iron seat inserts on intake valves and silicon-chrome-molybdenum seat inserts on exhaust valves on 61 cu. in. Extra deep cooling fins on all models
Upper left-A view of the new Harley-Davidson new 45 Twin motor with cooling fins on the crankcase and gear case cover Lower left-All 1937 models of Harley-Davidson have built-in instrument panel, with a large, easily read dial Upper right-Tubular chrome-molybdenum forks as will be used on the 61, 74 and 80 models Lower right-The speedometer is driven by spiral gears from the transmission in the Big Twin models