by which the motor is supported in the frame are substantial-ribbed members cast integrally.

The approved method of crank-case construction favored by the majority of engineers is shown at Fig. 119, bottom side up. The upper half not only forms a bed for the cylinder but is used to hold the crank shaft as well. In the illustration the three-bearing crank shaft is shown resting in the upper main bearing boxes which form part of the case, while the lower brasses are in the form of separately cast caps retained by suitable bolts. In the construction outlined the bottom part of the case serves merely as an oil container and protection for the interior mechanism of the motor.

Fig. 120. Bottom View of Inter-State Power Plant. Crank Case a Barrel Form with Removable Bottom Plate to Permit Access to Engine Interior. Important Power Plant Parts Clearly Shown.

In some instances where barrel-type crank cases are employed, instead of using hand holes for adjustment in the side, the design is as shown at Fig. 120. The bottom of the crank case is left open in casting and is closed by a large plate. The interior parts of the engine

Fig. 121. Top Half of Knox Crank Case. Note Method of Supporting Five-Bearing Crank Shaft and Substantial Yoke

Encircling Space for Fly Wheel and Serving to Hold Transmission Gearing to Form Unit Power Plant.

are clearly depicted, as they appear viewed from the bottom, and the accessibility afforded by this design should be readily perceived. Engineers who favor unit power plants often include a portion of the crank case with the housing for the clutch and gearset. Such a construction is clearly shown at Fig. 121. It will be seen that a substantial yoke member which encircles the fly wheel is used to join the gear case to the engine base. In this view the method of retaining the five-bearing crank shaft to the upper half of the case is also shown. In designing crank cases the main thing to be considered is to have it of ample strength and to arrange the various parts so that the interior mechanism may be reached without dismantling the entire engine when adjustments are necessary.

Typical Two-Cycle Motors.-As a general rule the two-stroke cycle engines that have been adapted for automobile propulsion differ materially from the simple forms previously described. Some makers, who use the simple form, have been able to secure very satisfactory results in practice by careful attention to port design. When a twocycle motor is to be used for motor-boat propulsion, it is a moderate speed proposition and great flexibility or efficiency are not sought. In the automobile, however, the conditions that obtain make it necessary to design the power plant in such a way that it would have a wide range of speed and so that it can be easily accelerated from its lowest to its highest speed without missing explosions or running irregularly.

A sectional view through the cylinder of the Amplex two-cycle motor is shown at Fig. 122, A. This motor is a simple construction which resembles the marine type in general design, though great care has been taken in proportioning the ports and gas passages to obtain the flexibility which is so essential to the motor-car power plant. This motor is a three-port type and the gas is taken into the engine base through ports which are uncovered by the piston when it reaches the end of its compression stroke. When the parts are in the position shown at A, the piston has reached the top of its stroke and the compressed gas in the cylinder is ready for ignition. At the same time. the inlet ports just at the bottom of the piston have been uncovered and the gas flows through the intake manifold from the carburetor. In the other view shown at B, the position of the parts when the piston has completed its power stroke is depicted. The exhaust port is

fully opened and the burned gases are discharged through it. Communication is also made between the engine base where the charge has received preliminary compression necessary to insure its transfer through the safety screen and the open ports in the cylinder wall. The entering fresh gas is deflected to the top of the cylinder by the deflector plate provided on the top of the piston, as is usual practice. The Amplex motor is a four-cylinder type and gives very satisfactory results in practice.

The Legros two-cycle motor, which is of French derivation, embodies a distributor valve and a peculiar arrangement of pistons. In this construction a stationary member is placed inside of the regular working piston and it is the space between these members that is utilized to store the gas taken in, prior to transferring it from the pump portion of the engine to the combustion chamber. The action is very similar to that of the usual form of differential piston motor. When the piston goes up on the compression stroke it draws in a charge of gas from the carburetor through the rotary distributor valve and up through the passage which joins the valve chambers to the space between the stationary and movable pistons. When the piston reaches the top of its stroke the rotary valve turns to such a position that it cuts off the carburetor from the pumping chamber and provides communication between the pumping chamber and the cylinder by means of the usual transfer passage and inlet ports cored into the cylinder wall. Otherwise the action is just the same as that of the more simple forms of engines. The construction of this motor is clearly shown at Fig. 123, and as all parts are clearly indicated the principle of operation should be easily grasped.

Another differential piston motor designed by a French engineer, Monsieur Coté, is shown at Fig. 124. In this a double-diameter piston is used and the cylinder is formed so that the smaller of these members fits the upper portion while the large end of the piston fits the correspondingly enlarged lower portion. The functions of compression and explosion of the charge take place in the smaller cylinder, while the lower member acts as a pump. On every downstroke of the piston a charge of gas is drawn into the annular space between the piston and cylinder wall, and on every upward stroke it is compressed and forced into the working cylinder adjacent. The construction out