The Locomotive Of Today

76 The Engine : Crossheads. metal are fitted on the lugs, as seen in section at D. These are held in position and prevented from turning by means of pins or cotters passing through them and the lugs; thus all the wear takes place on the caps, which are easily renewed when worn out. Ihe crossheads for two slide bars may be met with in greater variety than perhaps any other form ; in some examples they are opened out, and the rod end works between, a gudgeon pin similar to that at B being employed. Another type is made solid with the piston rod, the crosshead and the small end being “forked,’ with a gudgeon pin; the taper is thep in the rod, and the wear takes place in the crosshead, which is bushed for the purpose. In America two bars being largely used this crosshead is employed, being- known as the “alligator” type, and on express engines the upper face is orten made longer than the lower, it being worn most by the engine running chiefly forward; it is made of cast Steel, having wearing plates fitted above and below for renewai when worn. At E and F another form of crosshead is shown, it is of a type used for four slide bars, and consists of a socket which has also two cheeks continued back, and a gudgeon pin passing- through them. Between these the small end of the connecting rod takes its bearing-, whilst on the ends which are reduced somewhat in diameter and project about 3-in., the slide blocks are placed; the pin is prevented from turning- by having" a key or set pin inserted. The socket and pin are generally ot wrought iron case-hardened, the slide blocks are of cast iron, hollow if large, and often provided with holes filled with white metal upon the sliding surfaces. With this form of crosshead it is necessary.to have a small end with half brasses and a strap, as the pin cannot be drawn out to accommodate a solid eye, although some engines have provision for this, by having a long pin with a head and thread at its opposite end; this can be passed through the two blocks and secured with a nut, the pin being prevented from revolving as before, by a key or feather. 1 In any of these forms large bearing surfaces are an advan- tage, but it must always be borne in mind that heavy crossheads, being reciprocating parts, are difficult to balance, therefore they should be as light as possible, consistent with strength, and all wearing surfaces should be bushed, or pro- vided with wearing strips, as it is then much easier, as well as cheaper, to renew them; case-hardened wrought iron is perhaps the best metal, the wearing surfaces being ground up after the hardening operation has been performed, which is