The Locomotive Of Today

136 The Framing, Wheels, etc. : Coupling Rods. sink. These pins are either of Steel, or of wroght iron well case-hardened on the journal and ground up true. The coupling rods are either of iron or Steel, being usually made in one piece without welds. The cross section varies from a plain rectangle to different H sections, and is some- times parallel throughout, but perhaps more frequently thicker about the centre of the rod’s length. In some of the H section rods the grooves are deepened as they near the ends, thus leaving more metal in the middle, and strengthening the rod there, where experience has shown it is most liable to failure in service. The ends vary somewhat in shape, but the solid eye illustrated at M, with a bush inserted in it to take the wear upon the crank pin, is very largely used. The bush is, in some cases, of cast iron with a thin layer of white metal immediately round the pin, in others, of plain white metal or gun metal throughout, and sometimes in the latter metal with grooves of white metal inserted similar to those in the axle- boxes, etc. It is prevented from turning in the rod by means of a taper pin, as shown, which passes through a hole half in the rod and half in the bush, or by a bolt which is screwed up through a boss formed at the bottom of the rod, and enters a hole in the bush, as shown at N ; a nut upon the thread of the bolt locks it in position. In other cases the oil cup is separate from the rod, and is screwed into a hole at the top, the shank upon it being long enough to project into a hole in the top of the bush. A simple key answers the same purpose in other rods. In engines with more than four wheels coupled it is necessary that there should be freedom allowed for the rods to give vertically in their length, as the different pairs of wheels are moving over varying levels in running, and if they were in one rigid length they would be liable to be broken. A joint to allow of this movement is shown at N, where the prolongation of one rod has an eye for the reception of a pin which also passes through a fork upon the other length, the hole in the first mentioned rod is often bushed with a Steel bush, and the pin made a tight fit and held in the fork by a feather, so that all the wear is taken up in the bush, which can be easily renewed. Another method is to fork one rod and form the other with a large eye to go between the jaws of this fork. These take a gun metal bush large enough to form a seat for the crank pin. The fork is made a working fit upon the outside of the bush, and so the rods get the required hinge action. A longer crank pin is necessary in this case. Entirely separate