When the Model E was introduced, in 1936, it continued an embarrassing Harley-Davidson tradition. It had problems. Oil flow had always been a concern in Harley's engines. To be fair, it was troublesome to all engine makers in the first decades of internal combustion. In Harley-Davidson's early F-head engines, the oil lubrication was done by a system called "total loss."
The rider filled a reservoir alongside the gas tank and regulated oil flow from the tank by watching drops fall through a sight tube. Normal riding conditions called for three drops every five seconds. This oil worked its way down through the engine and finally dripped through a small tube onto the drive belt pulley shaft and later on to the front chain ring.
Harley-Davidson advertised that this system always provided clean oil to the engine and running gear. It was never mentioned that a moderate amount of that oil sprayed onto the rider's leg. A pump was added in l911 to give a few extra shots to the engine under heavier strain, when going up hill, for example. The rider's tendency was, when in doubt, better too much oil than too little. Some of that excess oil forced its way past piston rings, clogging valves, fouling spark plugs, and spreading more onto the rider's leg.
With the side-valve engines, an oil pump was linked to the throttle. The more twist of the wrist, the more oil. But it was tricky to regulate, and controlled as it was by a wire linked to the throttle's twist grip, wire stretching affected oiling. Plugs fouled. Engines ran sluggishly until the problems were finally sorted out. And they always were sorted out. That was a part of the developing mystique of Harley-Davidson.
The company always solved its problems. Sometimes these conditions--oiling and others--led plant superintendent William Davidson to literally shut down the production line, to ship no more motorcycles until the situations were remedied. This happened in the case of the first production Seventy-four flatheads, the 1930 V-series bikes.
All of this led not to a myth but to a suspicion, one that indian motorcycle dealers did their best to perpetuate: Haarley-Davidson may build a good motorcycle but it relies on its customers for development work. The Milwaukee-built bikes always seemed to leave the factory a few months before they were ready, a few thousand miles before they were thoroughly tested, just a short while before all the bugs were completely discovered. And squashed.
The l036 Model E 61 cubic-inch OHV engines continued the legacy. Oil-more accurately, lubrication--was still the problem. In 1934, Harley-Davidson upgraded its oil system by means of a more effective pump. Oil flow to the Harley valves and other parts had been inconsistent; it was either too little or too much but seldom was it just right.
The new 1936 OHV engine and its dry-sump, recirculating oil system was a valiant attempt. But this resulted in yet another crisis repair project that saw three versions of oil tanks and lines used in 1936. (Eventually H-D developed a gear-driven centrifugal-valve pump in the recirculating oil system that was introduced in 1941.
This new pump incorporated a valve that provided maximum lubrication to the engine at high speed. At low speeds, it directed the oil back to the supply tank, bypassing the gear case.)
The new Sixty-Ones admittedly had outside influences to contend with as well as internal ones. The Depression was at its height. President Franklin Roosevelt's National Recovery Administration strongly recommended that employers hire additional workers rather than incurring overtime among employees already on staff. This waas a recommendation that no employer dared to ignore. Harley-Davidson had not enough time and not enough payroll to solve this oil problem in time.
The new OHV engines provided forty horsepower at 4,800 rpm. The design continued the practice of shortening the stroke in relation to the bore. That allowed the steady increase in power from the F-head engines through the flathead engines to these new OHV engines. The performance improvement that the new engine brought about was necessary to wrest the technical lead from Indian, a company that, while feeling beaten and bruised by l936, was not yet on the ropes.
The bore-versus-stroke question is important to all engines. For any given displacement, bore and stroke vary in relation to each other, but increasing or decreasing one or the other has dramatic effects on engine performance. Longer stroke engines provide their power at slower speeds, more in the form of torque. Shorter stroke engines achieve their power at higher speeds. They develop less get-away-from-the-stop power but more high road-speed strength. But a shorter stroke gets a bigger cylinder diameter in the trade off. That allows room for larger valves to get more fuel in and more exhaust out.
Harley-Davidson's engine uses a split flywheel as a crankshaft. This is designed so that it brings the rear piston up to the top of the cylinder an instant--forty-five degrees of rotation--ahead of the front. Ignition of these two cylinders is provided by a single coil with a "siamesed" lead to both spark plugs. As a result, the two plugs fire each time that either one is needed. For example, because the reaar cylinder has compressed fuel in it when the piston is at top dead center, both plugs spark even though the front is approaching the top of the stroke to expel its exhaust gases.
The explosion powers the rear piston down and brings the front the rest of the way up and back down as it sucks in a fresh fuel mixture. The flywheel brings the pistons back up, compressing the front and emptying the rear. When the front plug is sparked into compressed fuel, the rear piston is already heading down, beginning to suck in fresh fuel. Slightly odd though this may be, this "phantom firing" was adopted in the earliest days out of a pursuit for simplicity. Unfortunately, this firing system also provided Harley-Davidson with its legendary vibration. Fortunately, it is largely responsible for the exhaust sound that these engines produce.
H-D found itself then in something of a dilemma. The engine could not grow because of the physical limitations imposed within the frame. And it could not turn faster because vibration would get worse. But faster--somehow--was necessary. More American roads were paved, and the competition was making road motorcycles capable of more than 100 miles per hour. So chief of engineering William S. Harley and his staff did what they could. They sset out to make the engines breathe better.
Some engine basics should be explained here. Overhead valves--such as those in the first F-heads--offered a big benefit. The fuel comes pretty much directly into the combustion chamber for ignition. In early Knucklehead engines, however, the valve stems, valve springs, and rocker arms were hung out into the airstream. This was good for cooling, but it was noisy and prone to damage from airborne dirt.