The Locomotive Of Today

The Engine: Shifting Link Motion. 89 obtained from the connecting rod and crosshead combined. These two latter gears are particularly suitable for engines with the valves above the cylinders. The shifting link, being the most common in Britain, will be considered first. It is illustrated in Fig. 18 as applied to an engine with inside cylinders, having the steam chest between them. Two eccentrics are fixed upon the crank axle between the cheeks of the cranks, being held by keys let halt into ways in the axle, and half into the eccentric sheaf. This latter is in two portions, held together by means of two bolts passing throug'h, with heads sunk into the smaller portion; cotters are driven through holes in the bolts at the other end, securingthe two half sheaves tightly together. Each eccentric is separate from the others, and four keyways are cut in the axle. To simplify this arrangement many builders now cast the eccentrics in pairs, so that only two keyways are necessary, and in some cases, to entirely dispense with keyways, which are always a source of weakness to the axle, the eccentrics are cast in pairs, and the outer ones have lugs on their outer sides, which project over and take a bearing' upon the cheek of the crank. This latter method cannot, however, be em- ployed when the cheeks are oval, as shown, or circular in shape, but only when flat. Steel or case-hardened iron set screws screwed through the sheaf, having sharp cupped ends to cut into the axle, and checked by a nut upon them, were at one time the only means employed to hold eccentrics upon the axles. Ihey are now retained on some railways in addition to the keys as a further precaution, but they are often dispensed with altogether. When the detached eccentrics, as in the sketch, are employed, the larger portion is of cast iron, and the smaller of wrought iron, but with the double eccentrics they are entirely of cast iron. The straps are made in brass, wrought iron, or, as now most frequently, of cast iron ; when of wrought iron, brass or cast iron liners are frequently used. F lat faces are provided upon them, on which the butt ends of the eccentric rods are fixed by two bolts. Oil receptacles are cast on those of cast iron or brass, and forged upon or attached to the wrought iron ones. The eccentrics are set upon the axle in such a position that the valves may have their proper amount of lead, with suitable allowance for lap. If there were no lap or lead allowed the valve would be made the width between the outer edges of the ports, and the eccentric would have to be set to exactly go° or a quarter of a revolution in advance of the