The Locomotive Of Today

The Engine : Links, Eccentric Rods. 91 cranks, in order to open and close the ports at the proper times, but as both lap and lead are always allowed on loco- motives, the sheaves have to be set slig'htly in advance of 90 , and this quantity is called the angle of advance, or angular advance of the eccentrics ; it will be seen on examination of the sketch how much is usually allowed. The throw of the eccentric, of course, primarily depends upon the widtli over the ports and when the eccentric rods are coupled up to the top and bottom of the link respectively, as in the sketch, so that the link can never be placed with the intermediate valve spindle and eccentric rod in one straight line, the travel of the eccentric must somewhat exceed the travel of the valve. Many makers have the eccentric rods coupled on to bosses on the back of the link, so that the throw of eccentric may be lessened. The link or quadrant is forged of iron, and after being machined all over is well case-hardened, the wearing surfaces being ground up and the pin holes in most cases fitted with bushes, which can be renewed when necessary ; these latter are often of Steel. Ihe pins are also of case-hardened iron, and are held in position by small taper pins passing halt through them. The link is hung- by suspension links, one on each side, from a weigh shaft placed above them and running- across between the frames. Lugs are rivetted with cold turned rivets, tightly fitting- the holes, on to each side of the link, and have pins, usually called the saddle pins, upon which the suspension links are placed. The centre of the point of suspension should be upon the centre line of the link, both vertically and horizontally, in order to get the best results. The curvature of the link is equal to the length ot the eccentric rods. The eccentric rods are of wrought iron with case-hardened ends, and are usually coupled up to the link with the fore gear rod to the top, and the back gear rod to the bottom. When coupled up as in the sketch, with the crank on the back centre and the eccentrics nearest to the link, the rods are described as open rods; if, however, the cranks and eccentrics remained as now, and the fore gear rod was coupled to the bottom and the back gear rod to the top, they would be called crossed rods, and the effect would be to reverse the amount of lead. With open rods an early cut off involves more lead, whereas with crossed rods early cut off requires less lead. Crossed rods are very seldom employed on locomotives in Britain, but sometimes in America. The whole weight of the link and hangin g gear, as well as part of the eccentric rods, etc., has to be raised when the