port C is uncovered. This permits the vacuum remaining to be displaced by air through the air valve B. As soon as the piston starts on its downward stroke the valve in A closes and the charge in the base is forced up through the transfer port D into the cylinder. This arrangement permits of a large, full charge of gas with consequently higher compression, more power, and freedom from crank-case explosions. In this motor the ports are placed in the forward and rear sides of the cylinders: by this method the piston and cylinders wear longer than if the ports were cut in the sides of the cylinder walls as the main thrust of a piston is sideways. Still another type of two-cycle engine is so constructed as to admit the charge from the base through a port in the piston walls and hence through a by-pass and valve in the top of the cylinder. The Smalley engine is of this design, and is illustrated in Fig. 14. On the upward stroke of the piston a charge of gas is drawn through the fuel inlet A into the crank case B. When the piston starts downward this vapor is brought under compression until the piston reaches the lowest point of its stroke, whereupon the port C in the piston comes into line with the port D in the cylinder, thus allowing the compressed gas to rush up through the by-pass E and through the valve F, into the top of the cylinder. At the commencement of the upward stroke of the piston the valve F closes by the spring G, and the gas held in the top of the cylinder is compressed and ignited; the piston is driven down and the exhaust gas passes out through the opening H, as usual. This motor has several advantages, not the least of which is the cooling effect on the piston of the fresh charge of cool gas rushing through it at each stroke. The fresh charge coming directly in from the head of the cylinder also serves to drive out all E D- G B Fig. 14. Smalley Motor traces of burnt gas and results in a cleaner and better charge for firing. The only disadvantage in this engine lies in the inlet valve in the cylinder head. This valve in time will wear and cause loss of compression and will require regrinding as often as the valves of a fourcycle motor, and to the ordinary operator grinding of valves is a bugbear. Moreover, if the valve sticks, or the spring breaks, the motor is temporarily put out of service, and usually such accidents occur at the most inopportune and critical times; a similar engine with mechanically operated valve might be more satisfactory. Several good motors of the two-cycle type are now constructed with an open base, or, in other words, without the closed crank case usually seen. This style of motor has many advantages over a closed-base engine. All the working parts of the crank, shaft, etc., are readily accessible for adjusting and oiling, and any danger of leakage and loss of compression in the base is obviated. An engine of this style of construction, made by the Powell Engine Co., is shown in Fig. 15. As will be seen by the diagram the piston P is hollow, and below it and above the base a compression plate A is placed through which the piston rod slides. Below the compression plate the piston rod is pivoted to the connecting rod B, at the cross-head C, which is a part of the same casting as the piston rod itself. On the upward stroke of the piston the gas is drawn into the space D, between the piston P and the compression plate A, through the inlet port E. On the downward stroke the gas is forced up through the by-pass F, to the port G, and thence to top of cylinder, exactly as in the ordinary two-port motor. After the explosion occurs the exhaust gases pass out through the port H. This motor possesses stronger compression than in a closed-base engine for forcing the charge into the |