Crankshaft and cylinders
Main bearing surfaces were babbit plain sleeve type. The crankshaft itself was made from a solid 100-pound block of high carbon or “tool” steel and, even though the Wrights were concerned about engine vibration, the crankshaft contained no counterweights. A heavy cast-iron flywheel would be keyed and shrunk to the crankshaft later to absorb the vibration. “I traced the outline on the slab,” Taylor recalled. “Then drilled through with the drill press until I could knock out the surplus pieces with a hammer and chisel. Then I put it in the lathe and turned it down to size and smoothness. It weighed 19 pounds and she balanced up perfectly, too.”
Cylinders were kept short for ease of cooling and more effective sealing with the water jacket. The piston skirts extended far below the bottom edge of each cylinder during operation. The cylinder barrels were made of cast (also called “grey”) iron and machined as thinly as possible, again to save weight, but also to create more efficient heat transfer to the water jacket. They were threaded into the crankcase at the lower end.
The pistons, also of cast iron, used three rings between the wrist pin and top. They were essentially all compression rings since they wanted oil to move freely throughout the engine for adequate lubrication. The wrist pin was locked in place with a set screw. There is some controversy on whether the original 1903 engine used an oil pump or simply used a “slinger” lubrication system. The connecting rod ends had scuppers to fling the oil from the crankcase sump area throughout the engine. Later Wright engines used a small oil pump, but Charlie Taylor, in later years maintained that the first engine did not use a pump.
Pistons and cylinder walls were not honed to a fine finish because the Wrights figured the explosive charge and forces in each cylinder would “lap” the piston and cylinder surfaces adequately during operation.
The connecting rods were a unique five-piece design. A steel tube was fitted with threaded tool steel adapters at each end. Attached to one end was a bronze casting/bushing that attached to the piston pin while the other end held another bronze casting that attached to the crankshaft. Steel pins held the bronze ends in place to the steel threaded adapters. Each of the four connecting rods had to be carefully measured (with ruled height and surface gauges accurate to 1/64 of an inch by eye) to be precisely the same length to avoid engine vibration.
The valve system, though unique to us today, was not that unusual for automobile engines of the time. The valves were located, opposite each other, in a horizontal tubular chamber that was threaded “T”-style to each cylinder barrel top thus creating the combustion chamber. The intake and exhaust valve heads were identical — each 2 inches in diameter made of cast iron. The valve stems were made of carbon steel and threaded into the heads, then peened over to hold them. The intake valve was the “suction-operated” type which meant it opened upon the downward motion of the piston as suction was created in the cylinder during the intake stroke. A small coil spring helped close the valve upon the piston’s return on the compression stroke. This eliminated several parts that would have been needed in a more complex open/close mechanism such as the exhaust valve used.
For the exhaust valve mechanism, a camshaft, made of hollow mild carbon steel, was mounted in the opposite side of the crankcase from the crankshaft on three babbit-lined bearings, and turned by a sprocket and chain (standard bicycle hardware). Cams were machined separately and sweated onto the camshaft. No pushrods were necessary as the cams pushed directly on the rocker arms. The cams had sharp opening and long duration profiles which the Wrights felt would enhance both quick exhaust of gases and effective scavenging for the incoming air/fuel charge. Efficiency and power adjustments were made by increasing the size and tension of the valve springs. The 1903 engine had an average compression ratio of 4.4 to 1 and mean effective pressure of 36 psi at 870 rpm (31 psi at 1,000 rpm).
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