The Gasoline Motor

by Harold Whiting Slauson

While the poppet valve motor is still used on the majority of automobiles, a new and radical type of valve mechanism has been giving successful results. This is known as the sliding sleeve type of motor, and while it has been used for several seasons in Europe, 1912 saw its adoption for the first time in America. The sleeve motor, it must be understood, is of the four-cycle type, the events occurring in the same order as on any ordinary automobile motor, and the only difference lies in the nature of the valves that control the openings of the exhaust and inlet passages. That this difference is great, however, will be realized when it is understood that the valves consist of two concentric shells, in the inner one of which the piston reciprocates. In other words, two hollow cylinders line the interior of the cylinder casting and replace the poppet valves and pockets of the more familiar type of motor.

These sleeves, or shells, or hollow cylinders—or whatever name it is chosen to give them—slide up and down in the same line of action as that of the piston. A port, or slot, is cut near the top on opposite sides of each of the shells. These four ports are so arranged that one set opens directly opposite the intake passage, while the other opens by the exhaust manifold entrance. When it is said that these ports open, it is meant that similar slots in the two sleeves come opposite each other, or "register," so that an unobstructed passage for the gas is offered. The port in one sleeve may be opposite the intake pipe entrance, but if the slot in the other sleeve does not correspond with this, the passage is effectively closed.

Thus it will be seen that the ports are opened and closed by the movement of the sleeves in opposite directions. For example, just before the opening of the intake port, the inner sleeves will be traveling upward while the outer shell moves downward, and the slots in the two shells will be opposite each other at the instant that they pass the inlet pipe. This gives a much quicker opening than would be the case if one shell stood still while the other moved downward, and it is because the slots approach each other from opposite directions that this motor can be run efficiently at high speeds.

Inasmuch as this is a four-cycle motor and the explosions occur in each cylinder but once during every two revolutions of the flywheel, each sleeve makes but one stroke for every two of the piston. The sleeves are operated by eccentrics attached to a shaft driven at a two-to-one speed by the crank shaft of the motor, and as they are well lubricated there is but very little friction generated between them and the piston. In fact, it has been shown that the power required to operate the sleeves, when well lubricated, is considerably less than that consumed by the springs and valve mechanism of the poppet valve motor, for the reason that the former type of valve does not open against the pressure of the exhaust, as is the case with the ordinary gas engine valve.

Besides the two- and four-cycle divisions, a motor is known by the arrangement of its cylinders and is classified as "cylinders cast separately," "cast in pairs," or "triple cast," according to whether there are one, two or three cylinders to a unit. The last-named type is not as common as are the "pair-cast" cylinders and of course can only be used on six-cylinder motors.

When all of the cylinders of a motor are cast in one piece, the engine is known as a "bloc" motor. This is a type that has come into popular use for small and medium-sized power plants during the past few years on account of the simplicity of its construction and the smooth and compact design that is rendered possible. Of course it may be argued that, with such a design, the entire set must be replaced if a single cylinder is damaged, but castings have been so improved that an accident or imperfection requiring the renewal of a cylinder is very rare.

It is evident that, beyond a certain size of cylinder, a bloc casting becomes too bulky to be handled conveniently, and as the entire casting must be removed when it is desired to reach the connecting rods, crank shaft, or piston rings, a motor so designed will seldom be found that develops more than forty or fifty horsepower. This type of casting is found on some six-cylinder cars, however, but it is naturally only the "light sixes" that will use such a motor.

Above six-cylinders, a motor is usually arranged with its power units set at an angle on either side of the vertical, thus forming the V-shaped motor. Several eight-cylinder motors are so constructed, the units being arranged four on a side and each set placed at an angle of about thirty degrees from the vertical. This gives the effect of two four-cylinder motors placed side by side and operating on the same crank shaft.

In order to make the motor as compact as possible, the cylinders are "staggered;" or, in other words, the cylinders of one set are placed opposite the spaces between the units of the other. It will be seen that the V-shaped design of motor shortens the power plant and enables it to be set in a much smaller space under the bonnet than would be the case were the cylinders placed one in front of the other, as in the four- and six-cylinder types.

As a rule, the two-cylinder, four-cycle motor is of a different type from its four- and six-cylinder cousins, and is known as a "horizontal opposed" engine. In such a motor, the cylinders are set lengthwise and the pistons operate opposite each other in such a manner that a "long, narrow, and thin" power plant is obtained that is especially well-suited for a location under the body of the car. In fact, this horizontal motor, which may, of course, be of the four-cylinder type, is the only shape that can well be used under the body or seat of a touring car. In some small runabouts, however, the "double-opposed" motor is used to good advantage under the forward bonnet, as in the "big fellows."