plant installation that is generally employed, the views at Fig. 54 are presented, these representing a typical four-cylinder power plant viewed from the front and rear, showing clearly the method of supporting the engine base by four arms and also outlining the position of the various auxiliary components. In some types of commercial vehicles the motor is installed at the front end under the hood as in pleasure car practice, but in other cases it is placed at practically the same point but under floor boards or driver's seat.

The advantages of the motor under the seat location may be very well summed up by saying that it permits more loading space and less over all or wheel base for a given carrying capacity. The shorter wheel base vehicle is especially valuable in congested city traffic, because it may be more easily controlled when driving in narrow thoroughfares, taking corners, or backing up to a loading platform. The main advantage advanced for the motor in front type of commercial vehicle is accessibility of power plant, which may be easily reached by raising the hood. This feature is not lost when the motor is placed under the seat, however, because all average adjustments may be made by raising the floor boards or by opening a hinged door at the side of the motor compartment. Some makers who install the motor under the seat arrange the components in such a manner that they may be removed as units permitting ready access to the motor and making for its prompt removal in event of overhauling or serious accident. Such a construction is shown at Fig. 55, which depicts a light truck with the seat and dash units removed from the frame. It will be seen that the dash unit includes the radiator, control levers, fuel tank and frame, for the support of the floor boards. The seat unit is separate and is designed to fit over the dash unit when it is in place on the chassis.

CHAPTER III

The Principal Parts of Gasoline Engines-Their Design, Construction, and Practical Application in Typical Power Plants-Treating of the Cylinders, Valve System and Valve Timing, Rotary Valve Types, Combination Piston and Sleeve Valve Operation, Ring and Distributor Valve Motor Construction.

THE improvements noted in the modern internal combustion motors have been due to many conditions. The continual experimenting by leading mechanical minds could have but one ultimate result. The parts of the engines have been lightened and strengthened, and greater power has been obtained without increasing piston displacement. A careful study has been made of the many conditions which make for efficient motor action, and that the main principles are well recognized by all engineers is well shown by the standardization of design noted in modern power plants. There are many different methods of applying the same principle, and it will be the purpose of this chapter to define the ways in which the construction may be changed and still achieve the same results. The various components may exist in many different forms, and all have their advantages and disadvantages. That all methods are practical is best shown by the large number of successful cars which use radically different designs.

Methods of Cylinder Construction. One of the most important parts of the gasoline engine and one that has material bearing upon its efficiency is the cylinder unit. Of late there has been a tendency to depart from the previous methods of casting the cylinders individu ́ally, or in pairs, and make all cylinders a unit or block casting. Some typical methods of cylinder construction are shown at Fig. 56. The appearance of individual cylinder castings of two different types are shown at A and B. In the former, the cylinder and cylinder head are cast integral and the valves are supported by inserted cages. In the cylinder design shown at B, the head member is a separate casting from that forming the cylinder, and the valves seat directly in this