The exhaust port opens (Fig. 31) when the lower edge of the slot in the inner sleeve leaves the junk ring in the cylinder head, the sleeve moving rapidly downward at the moment of opening. To obtain a rapid opening of the exhaust, the ports are arranged so that the inner sleeve is just about to reach its maximum speed at the time of opening. The outer sleeve closes the port (Fig. 33), closure starting when the upper edge of the outer sleeve coincides with the lower edge of the cylinder wall port. At this time the outer sleeve is traveling downward at maximum speed, so that the closing of the exhaust is as rapid as the opening. The lubrication of the Knight motor is accomplished by what is known as the movable dam system, which overcomes the tendency of the motor to over-lubricate. A movable trough is placed under each connecting rod, in the crank case, that is connected to the carburetor throttle lever in such a way that the opening and closing of the throttle raises and lowers the troughs. When the throttle is opened, raising the troughs, the points on the ends of the connecting rods dip deeper into the oil which creates a splashing of oil on the lower ends of the sliding sleeves. In this way the oil is fed to the engine in direct proportion to the load and the heat produced in the cylinder. When the motor is throttled down, the points barely dip into the oil. An excess of oil is fed to the troughs by an oil pump, which keeps them constantly overflowing. The overflow is caught in the pumps located in the crank case, and returned to the circulation so that it is used over and over again. Claims of great efficiency are made for this system, there having been many tests made showing 750 miles per gallon of oil, while even as high as 1,200 miles per gallon has been made under favorable conditions. The oil pump is contained in the crank case, and is of the gear type, insuring positive action. The pump also acts as a distributer, a slot being cut in one of the gears which register successively with each of the six oil leads. In this way it is possible to obtain the full pump pressure in each lead should they become obstructed in any way. In the upper half of the crank case are cored passageways through which the air passes before reaching the carburetor. These passages not only eliminate the rushing sound of the intake air, but also form an efficient method of warming the air supplied to the carburetor and cooling the crank-case. It is possible to furnish warm air after the engine has been idle for several hours, as the oil in the crank case remains warm longer than any other part of the engine. (50) Reeves Slide Sleeve Valve.