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.
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