The connecting rods were another homemade affair starting with a tubular steel center section with the small end consisting of a bronze casting that was threaded onto the tubular center and connected to the piston wrist pin. The big end of the rod was another bronze casting, also threaded onto the tubular center using steel pins with threaded adapters to complete the connection.
Each of these connecting rod assemblies were carefully assembled for length so that each was within 1/64-inch (0.333-inch) to ensure the engine would run smoothly! The rods had to be light because the 4-inch bore cast iron pistons were incredibly heavy with long piston skirts. Later Wright engines retained the use of these iron pistons and very wide rings. The Wright brothers also did not finish hone the cylinder wall, choosing instead to allow cylinder pressure to seat the rings over time thus lapping the bores! This seems horribly crude by today’s standards, but this was typical internal combustion standards in 1902.
There is some confusion among historical accounts regarding whether the original “A” engine used an oil pump for pressurized lubrication. A NASA website description of the “A” describes the use of an oil pump driven off the camshaft that sprayed oil on the piston cylinder walls. This oil then dripped down onto the main webbing to lubricate the main bearings. However, the men who have recreated the “A” engine at the San Diego Museum of Flight in Balboa Park and Taylor’s own description contends it was splash oiled and not fitted with an oil pump.
This cutaway illustration reveals many internal secrets of the original Wright engine.
The typical means of early connecting rod and crankshaft lubrication was the use of dippers on the ends of each connecting rod to scoop the oil in the crankcase to lubricate the rods and to splash oil the main bearings and pistons. The original “A” engine was damaged when a rogue gust of wind damaged the Flyer on the same historic flight day that also bent the crankshaft. When the engine returned to Dayton, the brothers used the original crankcase for an upgraded “B” engine and it is likely at that point that pressurized lubrication was added.
The Wrights did not extend lubrication to the valvetrain and it is assumed that the exhaust valve componentry received manual oiling from an oil can before each engine startup. Many aircraft and automotive engines of this era used what is called a total loss oiling system where the exposed valvetrain was splash oiled with excess allowed to leak off the engine. This is why most early pilots who sat directly behind the engine were always covered in a light sheen of engine oil. European aircraft engines used castor bean oil while domestic-built engines relied on a petroleum-based oils that were merely categorized as light, medium, or heavy viscosity oils.
While the cylinders were water cooled, the combustion chamber area was not. The chambers, positioned atop the cylinders were separate housings containing the 2.00-inch intake and exhaust valves and the spark mechanism. This configuration is referred to as a “T” design since the combustion chambers sat wide on the top of the cylinders, with the two valves on opposite sides resembling the letter “T”. Because these chambers were air-cooled, reports about early Wright engine operation mentioned how the tops of the cylinders glowed from the heat.
This is a photo showing raw castings of both the aluminum crankcase as well as the combustion chambers which are the four, T-shaped components. The large cylinder to the left is one cast iron cylinder. The restriction at the top of the cylinder is where the T-shaped chamber would attach. The cylinder bore threaded into the crankcase and then the T-head was also threaded to the cylinder.
Among the many unique features of this engine is that there was no mechanical actuation of the intake valve. Its valve spring was very light and downward piston motion created a vacuum in the cylinder. This significant pressure differential with higher atmospheric pressure on top of the intake valve pushed the intake valve open during the intake stroke. The simple tubular steel camshaft employed only exhaust lobes that were sweated onto the shaft in the proper orientation. The camshaft was located on the opposite (bottom) side of the crankcase located by three babbitt-lined bearing housings. The shaft was driven by a simple bicycle chain and sprocket assembly that was likely sourced from the bicycle shop.
The exhaust lobes were shaped for quick opening and closure with long duration and it soon became apparent that, as engine speeds increased in search of more power, this valvetrain was the cause of many subsequent engine problems. Close inspection will reveal that the exhaust lobes acting directly on the exhaust rocker arms. Later engines enjoyed revisions to the original exhaust lobe shape along with the use of stiffer valve springs as rpm increased.
Most historians believe lubrication for the original engine was simply provided by scuppers that pulled and splashed oil up from the connecting rods to the bearings and also to the pistons and cylinders.
Robert Bosch had by 1902 already patented what would eventually evolve into the modern spark plug and the Wrights were probably aware of its existence. However, they chose instead a much more complex configuration that Charlie Taylor called a “make-and-break” ignition system. This consisted of spring-loaded contact points set with one located on a fixed pin and the other connected to a movable arm triggered by an eccentric driven by a spur gear on a shaft driven by the camshaft. When a timed spark was required, the cam would push on the linkage and move the arm away from the fixed-point arm, creating an arc fed by an on-board magneto bolted alongside the engine. A lever attached to a sleeve mechanism was used to advance or retard the ignition timing. Generally, timing was retarded during startup and then advanced for more power. This was the same kind of technique used in automobiles at the time with a linkage located on the steering column.
The magneto supplied the spark energy during engine operation and was spun through a friction drive off the flywheel. The magneto wasn’t all that powerful, putting out only 10 volts and 4 amps. To supply voltage for starting, a set of dry cell batteries in a box were used. This battery box was left on the ground after the engine started, again to save weight. The start procedure involved two helpers turning the two propellers. The Wrights realized that torque from two props turning the same direction would make it difficult to turn the aircraft in the opposite direction of the torque, so they merely twisted the chain driving the port side propeller (pilot’s left) to spin that prop in an opposite rotation and thus creating counter-rotating props.
As mentioned previously, the engine was a flat four or laydown orientation that placed the cam, valvetrain, ignition trigger, and the exhaust all in the upper location of the engine. The “A” engine did not employ any kind of exhaust pipe. The spent gases merely exited the head from a series of slots cut into the outer portion of the chamber. The exhaust was unfortunately aimed directly at the pilot, who lay to the left of the engine looking at the Flyer from behind. Because the pilot had to have easy access to the ignition controls, this orientation aimed the exhaust directly at the pilot. Subsequent Wright engine revisions changed this in deference to pilot and passenger comfort.
The fuel system is certainly the simplest of all. Carburetors of the day were large, complex, and unreliable and the Holley brothers had only in that same year begun to build what would eventually evolve into the traditional Holley four-barrel carburetor. But that was literally a half-century in the future.
