Home  

CHAPTER XVI.

CONNECTING-RODS, SIDE RODS, AND WEDGES.

CARE OF LOCOMOTIVE RODS.
WHEN it is found that an engineer runs his engine for months on arduous train service, and has no trouble with his rods, he may safely be credited with knowing his business, and attending to it skillfully. In regard. to the keeping of the machinery in working-order, the engineer's duties are mostly of a supervisory nature. When piston-rings get blowing, when guides need closing, or when a pump gets working badly, he reports the matter; and the work is done so that the defect is remedied. With the rods it is different. Although he does not file the brasses himself, he exerts great influence, for good or evil, in the way he manipulates the keys, and by the care he takes of the rods. Injudicious keying of rods is responsible for more accidents than the mistakes in any other one direction, with, perhaps, the exception of the current mistake of the hind brakeman, who supposes there is no use in going back to flag when his train has stopped between stations.

FUNCTIONS OF CONNECTING-RODS.
The functions of rods being to transmit the motion of the pistons to the running-gear, they have very heavy duty to perform. The conflicting strains and shocks to which a locomotive is subjected while running over a rough track at high speed, are, in many instances, sustained by the rods: hence it is of special importance that this portion of the motion should be kept in good order. Main rods convey the power developed in the cylinders to the crank-pins by a succession of pulls and thrusts equal in vigor to the aggregate of steam-pressure exerted on the piston. To endure this alternating tension and compression without injury to the working parts, it is of the utmost importance that the connections should be close fitted, yet free enough to prevent unnecessary friction. In fitting up main-rod brasses, it does not matter in what position the crank stands, so long as it is convenient for doing the work. But, if the engine has been in service since the pins were turned, they should be calipered through their horizontal diameter when the crank is on the center; since it is well known that the pins have a tendency to wear flat on the sides at right angles to the crank's length. The back ends of the main-rod brasses should be fitted brass to brass; for that form of doing the work makes the most secure job, and gives the connection all the advantages of a solid box, preventing the straps and brasses from being knocked out of shape by hammering each other, a result that surely follows the open-brasses method of fitting back ends of main-rods. Leaving the forward end brasses a little open is not injurious to that connection, because the line of strain is not so varied as that of the back end.

EFFECTS OF BAD FITTING.
When the work of fitting a set of back-end brasses is completed, they should be put in the strap, and tried on the pin. If, after being keyed close together, they revolve on the pin without pinching, the fit is not too tight. It is of the greatest consequence, in fitting rod-brasses, to ascertain, beyond doubt, that the brasses have been bored out true, and that they fit in the strap so that the line of strain shall be in line with the cross-head and crank-pins. It occasionally happens, through bad workmanship, that when the back end of a rod is keyed up, and the front end not connected, the rod does not point straight to the cross-head pin, but in a line some distance to the right or left. The distance may be very small, yet sufficient to cause no small amount of trouble. By some pinching and jamming, a rod in this condition can be connected up; but it is almost sure to run hot. And a rod in this condition will never run satisfactorily till it is taken down and fitted by a competent machinist. The back end may be all right, and the forward end suffering from oblique fitting. This is even more common than the first case, and the effect is the same. A rod in this condition, besides displaying a tendency to run hot, will keep jerking the cross-head from side to side on the guides, and will probably make the cross-head chafe the guides at certain points. Rods never run cool, and free from jar, unless they are fitted to transmit the power in a direct line between the pins.

STRIKING POINTS AND CLEARANCE.
Before putting up main rods, the striking points of the pistons should be located and marked on the guides. Then, when the rods are put up, the clearance should be divided equally between the two ends. The identification of these points is of greater interest to the engineer who is running the engine than to any other person; for upon their correctness the success of his running may, to some extent, depend. An engine may go out with the clearance badly divided, and run all right for a few days, and the driving of a key may then cause the piston to strike the head. A forcible instance of this kind once came under my observation. A careless machinist, in working on main-rod brasses, had mixed the liners, and shortened the rod, till the piston began to touch the back head. When the engine was working light, there was just a slight jar; but, when the load was heavy, the jar became a distinct pound. The engineer could not locate the knock, and was disposed to think it was in the driving-box. One day that he slipped the engine badly, steam began to issue from the back cylinder-head, which was cracked by a blow from the piston. The cause of the pound was then discovered.

WATCHING RODS ON THE ROAD.
When an engineer starts out with an engine after the rod-brasses have been filed, be should make them a special object of attention. If he can not shake the connection laterally with his hands when there is room for movement within the collars, he should slack up the key till he can do so; for some one has made a mistake in fitting. So long as the rod passes the center without jar when the engine is working hard in full gear, the brasses are tight enough. After running a few miles with newly fitted brasses, the rod will generally need keying up; for liners that were comparatively loose when put up, get driven compactly together, leaving lost motion. Although a connection may be put together brass to brass, there is still some work left for the engineer to do in the way of keying. To do keying correctly needs considerable sagacity, especially in the case of side rods. In the case of back ends of main rods, the key should be got down as soon as possible, to hold the brasses immovably in the strap; but, after this point is reached, there should be no more hammering on the key. Some men persist in pounding down keys that are already snug, and the effect of their blows is to spring the brass out of shape. A key acts as a wedge, which it is; and, when the taper is slight, the blow imparted by a hammer roughly used, exerts an immense force in driving it down. Something must yield; and the brass gets sprung towards the pin, presenting a ridge for a rubbing surface, which heats, and causes delay. After the key is once driven tight home, its work is finished. If the pin then indicates lost motion, the rod should be taken down, and the brasses reduced. In the case of main rods, this should be done at the first signs of pounding; for lost motion entails heavy shocks upon the moving parts. The front end of main rods requires to be very carefully watched, and the connection kept free from jar. Where this part is kept regularly oiled, and free from lost motion, it gives scarcely any trouble; but let the wrist-pin of the common cross-head once get cut through neglect, and it is a difficult matter getting it in good running-order again. The style of cross-head where the pin is part of the casting, although greatly used, is a most awkward article to fit up and keep in shape. The form of cross-head which works between two guide-bars, and has its axis in line with the piston-rod, is becoming deservedly popular.

SIDE RODS.
Many attempts have been made to dispense with side rods, and they certainly are a troublesome part of the machinery to keep right; but no better means of connecting driving-wheels has yet been devised. The first method of coupling driving-wheels together, so that more than one pair might be available for adhesion, was by means of cogs and gearing. This was improved on by an endless chain working over pocketed pulleys; but even this was an extremely crude device, —working with tumultuous jerks, and a noise like a stamping-mill. One of the first real improvements, which George Stephenson effected on the locomotive, was the inventing of side rods. An essential element in locomotive construction needed to make side rods run with safety, is, that all the wheels connected shall be of the same circumference. There is a practice on some roads of putting new tires on wheels just as they come from the rolling-mill, without putting them in the lathe. Such tires are seldom accurate in size; and they cause no end of trouble, especially to side rods. This is one of the economical practices that does not pay.

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 roadbed, 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.

In refitting wedges, these defects should be removed, the pedestal face carefully straightened its entire length, and the wedge-back fitted to it. It is not only necessary that the pedestal face should be smooth, but that it should be straight its entire length. If not, when it becomes necessary to adjust the wedge, if the pedestal is high on the top end, the wedge is thrown out at the top, binding the box at that point, and allowing it to swing at the bottom.

IMPORTANCE OF HAVING WEDGES PROPERLY FITTED.
With the pedestal face in a proper condition to avoid displacement of the wedge, when moved to different positions on it, we should consider what will be the method of lining the wedges, and what duty they have to perform. This duty is merely to take up the lost motion between the pedestal and boxes; and that, from their shape, they readily do from time to time. While this duty is simple, the wedges ought to do it without affecting any of the other parts of the locomotive, a condition of perfection that can be reached only by having all the wedges perfectly parallel with the pedestals and with each other. If the first condition is not complied with, the result, as stated, will be the box swinging in the wedges. If the latter, then with the varying position of the boxes in the pedestal due to the engine settling on the springs, or to the change of position from the motion of the springs when the locomotive is running, we will have a varying distance between the centers of the wheels and length for the side rods.

Many of the complaints we hear of — rods not working properly, are owing to this defect in wedges not being parallel, by which the distances are varied, and a strain thrown upon the rods that not only affects them, but causes them in turn to bind the boxes against the wedges by trying to compress or extend to a length varying as often as the motion of the springs. While the motion of the springs is not much in proportion to the length of the wedges, and the varying distance between centers of wheels is in ratio to that proportion, if the wedges are not parallel, we must remember how often the motion is occurring, and that, no matter how slight the strain upon the rods may be, we are putting it on a part of the locomotive that requires the minutest adjustment to enable it to do its work properly and safely.

INFLUENCE OF HALF-ROUND BRASSES.
Driving-boxes fitted with a half-round brass have a tendency to close at the bottom. This tendency is continuous, and becomes most marked as the brass wears down, relieving the box of the strain put upon it by the tight-fitting brass. With a properly fitted brass, and a collar put up in good shape, the box can not close much: still, there will be enough looseness to cause a slight, pounding. During the first few days' service of a locomotive after new driving-brasses of this shape are put in, the compression on the brass, resulting from the weight of the engine, tends to close the bottom of the box, and permits the box to rock. This evil may be, to some extent, prevented by fitting the wedges slightly closer at the bottom. This closing of the box at the bottom is not only an evil and annoyance in itself by causing pounding, but is a further source of trouble by hastening the forming of a shoulder on the top of the wedge. The tendency at all times is for the axle-box to wear a shoulder at the top and bottom of its travel, even when the box retains its proper shape; but, when it is distorted by closing at the bottom, the rubbing surfaces are put out of the true plane, and wear takes place much more rapidly. While the springs retain their position, and impart to the axle-box a fixed range of motion, no serious effect is felt from the worn wedges. But when the locomotive is passing over rough frogs or bad rail-joints, where the motion of the spring is increased, the frame pounds down upon the box, which for a moment becomes fastened in the narrow space between the shoulders of the wedges; and an effort is needed for the box to relieve itself, and allow the spring to resume its motion. This causes the engine to ride hard in some instances, where the condition of the track makes the box catch frequently. Sometimes the box will be unable to relieve itself without assistance, and much loss of time and annoyance result when the wedge has to be pulled down to relieve the box.

The forming of the shoulder on top and bottom of the wedge may be anticipated and prevented by planing the part where the ridges form, leaving a face just the length of the box plus the space covered by the motion of the springs. Not only does this aid in preventing the box from forming a shoulder, but it also reduces the first cost of fitting the wedges by reducing the surface to be squared and finished true.

POSITION OF BOXES WHILE SETTING UP WEDGES.
With the wedges in a proper condition when the locomotive enters service, we yet must care for them and adjust them from time to time, when it is necessary to take up the lost motion between the pedestals and boxes. When doing this work, it is important that the position and condition of the driving-box should be considered. The position of the box should be such that the wedge may be set up to the proper degree of tightness with certainty and without much labor. It is important that a wheel position be found where the box would not be moved by the wedge when the latter is being adjusted. This position will be found where the box is up against the dead wedge, since the lost motion will then be between the box and the wedge to be moved. To get all the driving-boxes in that position at one time is a difficult matter, if it is to be done by pinching the wheels. The position of the rods decides the direction of their action on the wheel by the thrust or pull upon the crank-pin. If the rod is above the wheel center, pinching behind the back wheel will force both the wheels and boxes on that side up against the dead wedge; but, should the rod be below the wheel center, similar work with the pinch-bar will draw the forward box away from the dead wedge, the side rod doing this by pulling on the crank-pin, this is always supposing the dead wedge to be in the front pedestals. The best position, therefore, to get an engine into for setting up all the wedges, is, with the side rods on the upper eighths; for then pinching behind the back wheels will push all the boxes up to the dead wedges. The work can then be done without putting unnecessary strain upon the wedge-bolts, which are often found with the corners of the heads rounded off, and the thread injured to such an extent that it will not screw through the binder-brace,—a condition of matters nearly always caused by trying to force up wedges without putting the engine in the proper position. If the wedge-bolt, from faulty construction, or through injury, is unable to move up the wedge, driving is resorted to, by which means it is battered on the end; and the jarring of each blow causes the ashes and dirt on top to fall behind the wedge, throwing it out of parallel, and introducing material that will cause the wedge to cut. The ashes and dirt that accumulate so readily on the top of wedges and boxes cause no end of trouble, although the fact is not generally recognized; and it will generally be fruitful labor to have these parts well cleaned off before beginning to set up wedges. Many complaints that are made, of wedges not being properly adjusted, proceed from the disturbance that follows grit introduced between the wedge and box.

NECESSITY FOR KEEPING BOXES AND WEDGES CLEAN.
The growing practice of close and stated inspection of locomotives to detect defects, before waiting for them to develop into breakages that cause trouble and delay to trains, will give especially good results if applied to boxes and wedges. If the wedges are taken down and examined at regular intervals, the ridges that appear so readily on the face, when oil-grooves are cut on the sides of the driving-box, can be smoothed off before they cause distortion of the surface. This is also a good time for a thorough cleaning of the pedestals and box, and the oil-holes can be examined and opened out properly. Work of this kind often prevents boxes getting hot on the road, with all the entailed delay and expense, which frequently include changing engines if the train must be pushed on. One turn of a hot box will often wear a brass more than the daily running for two years.

TEMPERATURE OF THE BOX TO BE CONSIDERED.
One condition of the box to be considered, when adjusting wedges, is its temperature at the time the work is done, and what that will be when the engine is in service. Adjusting wedges is often done as a preliminary step to lining and adjusting side rods; and this is done, on many roads, on the shop-day when the locomotive is in for washing out and periodical repairs. At that time, the engine being cold, the boxes will be at their lowest temperature, and, consequently, at their smallest dimensions. Allowance should then be made with the wedges for some expansion of the boxes. Another condition that should be considered, is how the box has been running. A box that has been running hot or warm, generally compels the wedge to be lowered to allow for extra expansion. When this box has been repacked, or otherwise cared for, the wedge is again set up. While doing this, it should be remembered that a box that has been running hot is liable to be distorted, and its journal bearing injured, so that it is likely to run warm for some time, till the brass comes to a smooth bearing. If the wedge will not permit the box to expand, it binds the journal, and is likely to run still hotter, and is liable to stick in the jaws.

SMALL DISORDERS THAT CAUSE ROUGH RIDING.
Many complaints are made about pounds in driving-boxes and wedges, when the trouble really exists elsewhere. Boxes with driving-spring saddles whose foot is but the width of the top or spring-band, will oft-times, if the band is not rounded where it rides on the saddle, or is not fitted with a pin or other center bearing, tip on the box with each motion of the spring. Or, if the saddle is moved from its worn seat on the top of the box, it will rock and pound. Again, obstructions in the bearing of the spring equalizer that will prevent the full motion of the springs, and bring them to a sudden stop, will produce a motion resembling that caused by a stuck box. Attention to details that are sometimes considered the crude parts of a locomotive, will often prove highly beneficial to the working of the locomotive; and especially is this the case with the parts that transmit the motion of the springs.


Table of Contents | Contents Page

Home
Do you have any information you'd like to share on this subject? Please email me!
The Catskill Archive website and all contents, unless otherwise specified,
are 1996-2010 Timothy J. Mallery