_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, he 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 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.
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.