ADJUSTMENT OF SIDE RODS.
To connect driving-wheels so that they will run together in perfect harmony, after ascertaining that they are the same size, the next point is to secure the crank-pins at an equal distance from the centers of the wheels. When this is done, and the wheels are trammed parallel to the line of motion, the rods will move on a plane with the centers of the crank-pins exactly the same distance apart as are the centers of the driving-axles. The rods can be adjusted to the greatest advantage with the steam raised, so that the heat of the boiler will make the frames about the same length as when the engine is at work. The expansion due to the heat of the boiler is short when measured by a foot-rule, but it affects the smooth action of the side rods to a remarkable extent.
Before tramming for the side rods, it is necessary to have the driving-box wedges set up just tight enough to let the driving-boxes move vertically in the jaws without sticking. The distance between the centers of the driving-axles and the centers of the crank-pins having now been found equal, the rods are fitted up; each connection being secured a close fit to the pin, with the brasses held brass to brass. With the brasses bored out exactly to the size of the crank-pins, and the rods accurately fitted, a connection could be made which would bind the two sets of drivers to move as an unbroken unit, were it not for the disturbing element which appears in the shape of rough track. With uneven track and worn wheel-tires, a tremendous tension is put on the rods where the connections are closely fitted. Provision is made for this source of danger by leaving the brasses of the back pins loosely fitted. A yielding space is left between the brass and the pin, not between the brass and the key or strap. The latter connections must be perfectly snug, or the strap will soon be pounded out of shape.
In the case of ten-wheel and consolidation engines, the brasses of all wheels behind the leading pair should be bored out one-sixty-fourth larger than the pins, which will generally be sufficient. In case a pin is sprung,—which is no rare circumstance,—room enough must be left in the brass to let the pin pass over its tightest point without pinching. The center is the proper position to put up side rods on. Some men like to fit side rods with the cranks on the eighths position; holding that there the greatest strain comes on, and, consequently, that there fitting up should be done. That is a mistaken idea; for rods may be put together on the eighths, and yet bind the pins badly in passing the centers. On the other hand, if they pass the centers easily, they will go round the remainder of the circle without danger.
KEYING SIDE RODS.
When it is necessary for an engineer to key up side rods, he should select a place where the track is straight, and as even as possible. Then he should put the cranks on the center, and take care that he can move the connections laterally after the job is done. If he now moves the engine so that the cranks are on the other center, and finds that the rod connections can still be moved, that side is all right. If the other side be treated in a similar manner, his rods are not likely to give trouble. With a worn-out engine and rough road-bed, it is a difficult matter to preserve the true mean between loose and tight side-rod connections. But, in a case of doubt, the loose side is the safe side. Yet most engineers are inclined to err on the side of danger, for they will generally tighten up the rods to prevent them from rattling. On a Western road, where solid-ended brasses were adopted, it was often amusing to hear the engineers protesting against the noise the side rods made when the brasses began to get worn. They would rattle from one end of the division to the other; but they would not break pins, or fracture themselves, and tear the cab to pieces, or ditch a train, as happens so often from other rods being keyed to prevent noise. Sprung crank-pins and broken side rods are very often the result of injudicious keying.
DIFFICULTY IN LOCATING DEFECTS.
A locomotive has so many parts that bear a close relation to each other, and that are so sympathetic when one of the parts becomes disordered, that it is sometimes a difficult matter to immediately locate a complaint. One of the signs of a defect, in many of the parts, or one of the consequences of it, is a “pound,”—a complaint that we hear of in a locomotive about as frequently, and with the same feeling, as we do of malaria in the individual.
POUNDING IN DRIVING-BOXES AND WEDGES.
But we will deal now with the pounds in a locomotive, and will take the location in which we find the most and serious ones,—namely, in the driving-boxes and wedges,—and see why they pound, and what will prevent them from doing so. The cause we will find, if in the wedges, is due to a rocking of the box in them, or from causes arising from imperfect fitting when they were put up, or lined up when the engine was in the shop. This fitting of wedges on a locomotive that has done service is a matter of importance in the immediate present and future working of the parts themselves, and of other parts of the locomotive as well. On stripping a locomotive that has done much service, it will be found that the working of the wedges on the face of the pedestal has worn it hollow, or pounded furrows on it, or has done both. This occurs so frequently on the “live” wedge side, that it may be taken as the rule, rather than the exception, to find the pedestal in this condition. While it does not happen so frequently on the “dead” wedge side as on the other, it will be found there also if the wedge has not been held by a fastening to the pedestal, or securely fitted between the top of the frame and the pedestal binder-brace. These defects will be found on the back of the wedge also, and are produced by the same cause and same motion as those on the pedestal face. These defects are the most frequent cause of the driving-box pounding, or of the wedges rocking; since thereby the wedges get thrown out of parallel to each other, when it becomes necessary to adjust them during the service of the locomotive.