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ADJUSTING SIDE AND MAIN
RODS
The proper adjustment of the side rods is a somewhat difficult
task, and requires the exercise of considerable patience on the part of
the Engineer who is careful to get them exactly right. It should always
be done while the boiler is under a pressure of steam. Sometimes it will
be necessary to put them up and take them down several time before they
are satisfactorily adjusted. Before placing them in position, the main
centers should be trammed from the center marks. After setting up the wedges
snug, a few trips should be run in order to ascertain whether or not they
are so tight as to require letting down, which should be avoided if possible
after the rods are adjusted. The wedges being right, the side rods should
be taken down and the pins examined to see whether they do not require
re-turning. The side rod brasses should then be reduce to the pins, the
brasses when keyed up being left brass and brass. The straps should then
be adjusted with the brasses in their places,
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the latter keyed up tight and then the exact center of each brass on
both ends of the side rods should be obtained. The side rods being thus
ready for tramming, the main centers should be trammed alike on both sides,
equidistant from center to center, and the same tram may be used on the
pin centers, and should they not be exactly right, as is often the case,
the rear driving wheels should be slipped until they come right. The main
centers and the pin enters being alike, the side rods may be trammed with
the same tram, applying it from center to center of the brasses, putting
in or taking out "liners" to bring them exact. The key should then be driven
down hard and marked next the strap with a scribe or knife. When this is
accomplished on both sides and the distances between main centers, pin
centers and brass centers are exactly the same, the side rods may be put
up, driving the key to the mark made while tramming, and the work is then
properly done.
Frequently a side rod will get to short or too long wearing
or keying of the
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brasses. It is then essential that the rod should be adjusted to the
proper length, and before it is taken down the end which remains in position
should be keyed up. In adjusting the right hand rod, the cross-head should
be placed on the extreme forward center, when a screw-jack may be place
for convenience sake under the strap end of the rod and the strap slipped
back so that the liners back of the brasses may be reached, when they may
be lessened or increased as required. There should be as many liners back
of the inside brass as it will take without wedging the pins apart, while
as many should be placed behind the strap brass as will permit the bolts
and key to occupy their proper position through the strap and rod,. The
rod should then be keyed up as tight as possible, shaking it with one hand.
In the case of an old engine, or one that has been out of the shop from
twenty to thirty-six months, it is important that the cross-head should
be placed on the extreme forward center on the side of the engine form
whence the rod is removed. In such an engine, the pins are likely to be
worn out of round where
Page 35
the friction is greatest, and that point is from the forward side of
the main pin to the following quarter. When a rod is keyed up it should
always be keyed on the largest part of the pin, so that when the engine
is moving the brasses will not bind upon the pin, and the rod will ten
run cool and give no trouble.
A word or two is also proper in reference to adjusting the main
rods. In all cylinder there is, or should be a clearance of from one-quarter
to three-eight’s of an inch, to prevent the piston form striking the
cylinder-heads as the rod varies in length by reason of wear or from unequal
lining and keying of the brasses. The clearance should be equally divided
in both ends of the cylinder in the following manner: First, key up the
main rod, that all lost motion maybe taken up, then ascertain the extreme
travel of the piston at both ends of the stroke by placing the cross-head
on the extreme center forward and back, making a mark across the guides
and cross-head. These marks will be the traveling points of the piston,
The striking points of the piston should then be
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obtained by disconnecting the main rod, prying the cross-head back until
the piston strikes the cylinder-head and making a mark from the mark first
made on the cross-head across the guides, which will be the striking point
at the back end of the cylinder Then pry the cross-head forward until the
piston strikes the forward cylinder-head, and a mark as before will constitute
the striking point at the forward end. The difference between the traveling
point and the striking point, will be the clearance of the piston in the
cylinder, and it should be divided equally in both ends by taking out or
inserting liners. The use of a jack under the rods when putting on the
strap renders its adjustment to the proper length much easier. A rod may
be shortened by taking out liners between the rod and the brasses and putting
them in the strap behind the brasses, and lengthened by reducing in the
strap and putting them forward of the brasses next to the rod. Putting
them between the brasses and the rod has the effect only to raise the key.
And when the brasses are filed, as is often the case, it is only necessary
to
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insert a thin liner to keep the key raised to its proper place. In reducing
brasses the usual rule is to put the same or sufficient thickness in liners
back of the brasses as is taken from the brasses , to keep the rod the
same length, and also keep the key raised to the proper height. Special
care should be taken, as the Engineer will generally find it necessary
to use his judgment as to the thickness of the liners. The edges of the
brasses should always be rounded off well, no matter how accurately they
may be fitted to the pin , otherwise they are liable to run hot. For example,
where brasses on two different rods are reduced, one set being rounded
and the other left square, it will be found that the former will run the
longest and with much less liability to heat. Rounding the brasses is especially
advantageous on engines and tender trucks. The attention of engineers is
called to this more particularly, because of the fact that most men, in
reducing brasses, do little more than take off the sharp edge. They should
be rounded at least one-eighth of and inch on the edge, and three-eight’s
back from the edge.
Chapter
1 - Introduction
Chapter
2 - Locomotive
Chapter
3 - The Fireman
Chapter
4 - Advice to Young Engineers
Chapter
5 - Tramming and Center Marking
Chapter
6 - Adjusting Side and Main Rods
Chapter
7 - Pumps and Pump Valves
Chapter
8 - Cylinder and Cylinder Packing
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