240 SMITHSONIAN' CONTRIBUTIONS TO KNOWLEDGE VOL. '27 



than the bore. The outer piston ring was .0035 inch narrower than its groove, 

 the second one .003 inch, the third .0025 inch, and the inner one .002 inch nar- 

 rower than its groove. The rings were bored one-sixteenth inch off center with 

 the exterior surface, and had one-eighth inch diameter of spring. They were 

 of the lap-joint type, with the sides of the laps carefully fitted and only one- 

 sixty fourth-inch clearance at the ends of the laps to allow for thermal expan 

 sion. As no grinding facilities were obtainable in Washington, the cylinders 

 were carefully bored smooth and free from taper, and the pistons were worn 

 in to a perfect fit by running them in by a belt for twenty-four hours, with 

 copious oil supply. 



The main connecting rod was f-inch diameter and solid, while the other four 

 were of the same diameter but with a |-inch hole in them. The gudgeon pins 

 in the pistons were hollow steel tubes Much diameter and case-hardened, and 

 were oiled entirely by the oil thrown off by centrifugal force from the crank- 

 pin bearing, the oil running along the connecting rods and through suitable holes 

 at the heads into oil grooves in the bronze bushings in these heads. 



Since on an engine for an aerodrome the best plan for releasing the exhaust 

 gases from the engine is to get rid of them as soon as possible, so long as they 

 are released behind the aviator and do not interfere with his view in the di- 

 rection of motion, it was decided to have the gases exhaust immediately from 

 the combustion chambers; but in order to prevent their playing on and heating 

 the main bearing of the crank shaft in the port drum the combustion cham- 

 bers were each provided with a chamber below the exhaust-valve seat, with a 

 side outlet therefrom. The manifold pipe through which the gaseous mixture 

 was supplied to the inlet valves of the engine consisted of a tube bent to a 

 circle and having five branch tubes, each leading to one of the automatic inlet 

 valves, which fitted removable cast-iron seats fastened by a nut in the upper 

 part of each combustion chamber. The very small amount of clearance between 

 the engine and the frame necessitated that this pipe be cut in three places and 

 joined by flanges in order to properly assemble it on the engine when the latter 

 was mounted in the frame. The carburetor, which was placed near the rear of 

 the aviator's car, was connected through suitable pipes to this circular inlet 

 pipe, at a point horizontally in line with the center of the shaft. The auxiliary 

 air valve consisted of a sleeve rotatably mounted on the vertical pipe leading 

 from the carburetor to the manifold, holes in the sleeve being brought to coin- 

 cide more or less with holes in the vertical pipe, by the operator, when more or 

 less air was required or when he wished to vary the speed of the engine. The 

 ling water for the jackets of the cylinders was led to them through a circu- 

 lar manifold pipe on the starboard side connected by a vertical pipe with the 

 centrifugal pump situated al the lower point of the lower pyramid of the aero- 

 drome frame. The heated water was led from the jackets through another cir- 



