17 A). The up-and-down motion of this large half of the piston acts as a gas pump and alternately draws in gas to fill the lower half of cylinder or base, H, and forces it out under considerable pressure. When the slightly compressed gas is driven out of the base it does not at once find its way up through a by-pass and port into the same cylinder as in the ordinary motor, but, through the agency of a gas "distributor," is introduced to the firing chamber of another cylinder. This "distributor," which is the essential portion of the Elmore motor, consists of a revolving cylinder B almost surrounded by another cylinder C. The chambers thus formed are provided with long ports running lengthwise; those of one chamber opening on one side of the distributor D and those of the other chamber opening on the opposite side E. In operation the distributor is revolved within its casing by a silent driving chain from the crank shaft, each end being supported by spindles and ball bearings.

In action each lower half of a cylinder receives gas drawn through the outer chamber of the distributor. This gas under low compression is then returned to the inner chamber of the distributor, from which it is led into the firing chamber of the cylinder whose piston is just commencing the ascending or compression stroke. Compression and explosion then follow exactly as in any other engine, and the operation is repeated in each cylinder in proper order, thus giving four explosions or impulses to the crank shaft with cranks set at 90-degree angles.

It must be borne in mind that the chambers of the distributor do not extend through its entire length. The

inner chamber B is divided at its centre, thus dividing the distributor into two equal parts. These two parts are connected by means of a by-pass F which is opened or closed by the operation of the throttle G. Until the throttle is opened half-way the two halves of the distributor operate independently, with the result that the cylinders work in pairs. When the throttle is halfopened the central control automatically opens and the power of the motor is then at once increased through all four cylinders operating alternately.

This Elmore motor, although apparently complicated, is in reality far simpler and has less parts than the ordinary four-cycle engine. Although advertised as a "valveless" motor, it is not strictly a valveless engine, for the "distributor" is actually a sort of rotary valve. The motor may therefore be considered a rotary-valve two-cycle motor. There is no doubt of the high efficiency of this engine, and its design and construction mark a great advance in two-cycle engines. The loss of base compression, unequal distribution of gas, loss or waste of fuel, and various other defects of the ordinary twocycle engine are entirely overcome in the Elmore, and its flexibility, power, reliability, and economy of fuel are fully equal to many, if not all, six-cylinder, four-cycle motors of equal rating. In comparison with fourcylinder, four-cycle motors of the ordinary type, the Elmore is far ahead. The trouble and difficulties experienced with poppet-valve, four-cycle motors is absent in the present motor, but the revolving distributor, chains, numerous rotating ports of the distributor, and the various other parts must be perfectly timed and

free from any lost motion or undue wear to work satisfactorily. These various parts of the rotating mechanism render the motor far more complicated than the regular two-cycle machine and it is therefore doubtful if this type of motor is so well adapted to the ordinary needs of the gasolene-engine user as either the regular two- or fourcycle engine. As a vehicle motor it is most efficient, and for this purpose for which it was designedthe rotary distributor is no objection. For small boat or stationary use, however, the simplest engine is the best, and motors for this purpose should be selected which can be readily repaired, adjusted, or taken down and cleaned by inexperienced hands.

or:

Two-cycle motors, as well as those of the four-cycle type, are usually made in either one, two, three, four, six cylinders. The operation of a multiple-cylinder, twocycle engine is practically the same as in a single-cylinder, but certain parts are slightly different in construction and design. In a two-cylinder motor the piston of one cylinder is on the downward stroke while that of the other is on the upward stroke, or, in other words, the cranks of the shaft are set opposite one another or at an angle of 180 degrees (Fig. 18). In a three-cylinder motor the cranks are set at 120 degrees (Fig. 19), while in a four-cylinder motor the cranks may be set at 90 degrees (Fig. 20 A), or at 180 degrees as shown in Fig. 20 B, C.

Three-cylinder motors have some advantages over the two- or four-cylinder machines, but they are more difficult to time correctly and either two- or four-cylinder engines are more widely used.

A multiple-cylinder motor will not deliver as much power in proportion as the same number of cylinders in separate motors, but on the other hand they run far more steadily and with less vibration than the singlecylinder engine. Moreover, they are easier to control and if one or more cylinders fail to work the engine will

Fig. 21.-Cylinders en bloc

usually operate on the remainder, and while in action the faulty cylinders may be adjusted until all are in running order. Few multiple-cylinder engines will carry a full load when any of the cylinders fail; and as a rule such engines, as well as all but the smaller singlecylinder motors, should be provided with a clutch, or gear, so that they can be run free from a load when so desired.

Multiple-cylinder motors have numerous disadvan