HOW TO MANAGE A TRACTION ENGINE.
A traction engine is usually the simplest kind of an engine made. If
it were not, it would require a highly expert engineer to run it,
and this would be too costly for a farmer or thresherman contractor.
Therefore the builders of traction engines make them of the fewest
possible parts, and in the most durable and simple style. Still, even
the simplest engine requires a certain amount of brains to manage it
properly, especially if you are to get the maximum of work out of it at
the lowest cost.
If the engine is in perfect order, about all you have to do is to see
that all bearings are properly lubricated, and that the automatic oiler
is in good working condition. But as soon as an engine has been used
for a certain time, there will be wear, which will appear first in the
journals, boxes and valve, and it is the first duty of a good engineer
to adjust these. To adjust them accurately requires skill; and it is
the possession of that skill that goes to make a real engineer.
Your first attention will probably be required for the cross-head and
crank boxes or brasses. The crank box and pin will probably wear first;
but both the cross-head and crank boxes are so nearly alike that what
is said of one will apply to the other.
You will find the wrist box in two parts. In a new engine these parts
do not quite meet. There is perhaps an eighth of an inch waste space
between them. They are brought up to the box in most farm engines by a
wedge-shaped key. This should be driven down a little at a time as the
boxes wear, so as to keep them snug up to the pin, though not too tight.
You continue to drive in the key and tighten up the boxes as they wear
until the two halves come tight together. Then you can no longer
accomplish anything in this way.
When the brasses have worn so that they can be forced no closer
together, they must be taken off and the ends of them filed where they
come together. File off a sixteenth of an inch from each end. Do it
with care, and be sure you get the ends perfectly even. When you have
done this you will have another eighth of an inch to allow for wear.
Now, by reflection you will see that as the wrist box wears, and the
wedge-shaped key is driven in, the pitman (or piston arm) is lengthened
to the amount that the half of the box farthest from the piston has
worn away. When the brasses meet, this will amount to one-sixteenth of
an inch.
Now if you file the ends off and the boxes wear so as to come together
once more, the pitman will have been shortened one-eighth of an inch;
and pretty soon the clearance of the piston in the cylinder will
have been offset, and the engine will begin to pound. In any case,
the clearance at one end of the cylinder will be one-sixteenth or
one-eighth of an inch less, and in the other end one-sixteenth or
one-eighth of an inch more. When this is the case you will find that
the engine is not working well.
To correct this, when you file the brasses either of the cross-head
box or the crank box you must put in some filling back of the brass
farthest from the piston, sufficient to equalize the wear that has
taken place, that is, one-sixteenth of an inch each time you have
to file off a sixteenth of an inch. This filling may be some flat
pieces of tin or sheet copper, commonly called shims, and the process
is called shimming. As to the front half of the box, no shims are
required, since the tapering key brings that box up to its proper place.
Great care must be exercised when driving in the tapering key or wedge
to tighten up the boxes, not to drive it in too hard. Many engineers
think this is a sure remedy for “knocking” in an engine, and every time
they hear a knock they drive in the crank box key. Often the knock is
from some other source, such as from a loose fly wheel, or the like.
Your ear is likely to deceive you; for a knock from any part of an
engine is likely to sound as if it came from the crank box. If you
insist on driving in the key too hard and too often, you will ruin your
engine.
In tightening up a key, first loosen the set screw that holds the key;
then drive down the key till you think it is tight; then drive it back
again, and this time force it down with your fist as far as you can. By
using your fist in this way after you have once driven the pin in tight
and loosened it again you may be pretty certain you are not going to
get it so tight it will cause the box to heat.
WHAT CAUSES AN ENGINE TO KNOCK.
The most common sign that something is loose about an engine is
“knocking,” as it is called. If any box wears a little loose, or any
wheel or the like gets a trifle loose, the engine will begin to knock.
When an engine begins to knock or run hard, it is the duty of the
engineer to locate the knock definitely. He must not guess at it. When
he has studied the problem out carefully, and knows where the knock is,
then he may proceed to remedy it. Never adjust more than one part at a
time.
As we have said, a knock is usually due to looseness somewhere. The
journals of the main shaft may be loose and cause knocking. They are
held in place by set bolts and jam nuts, and are tightened by simply
screwing up the nuts. But a small turn of a nut may make the box so
tight it will begin to heat at once. Great care should be taken in
tightening up such a box to be sure not to get it too tight. Once a box
begins to cut, it should be taken out and thoroughly cleaned.
Knocking may be due to a loose eccentric yoke. There is packing between
the two halves of the yoke, and to tighten up you must take out a thin
layer of this packing. But be careful not to take out too much, or the
eccentric will stick and begin to slip.
Another cause of knocking is the piston rod loose in the cross-head.
If the piston rod is keyed to the cross-head it is less liable to get
loose than if it were fastened by a nut; but if the key continues to
get loose, it will be best to replace it with a new one.
Unless the piston rod is kept tight in the cross-head, there is
liability of a bad crack. A small strain will bring the piston out of
the cross-head entirely, when the chances are you will knock out one or
both cylinder-heads. If a nut is used, there will be the same danger if
it comes off. It should therefore be carefully watched. The best way is
to train the ear to catch any usual sound, when loosening of the key or
nut will be detected at once.
Another source of knocking is looseness of the cross-head in the
guides. Provision is usually made for taking up the wear; but if there
is not, you can take off the guides and file them or have them planed
off. You should take care to see that they are kept even, so that they
will wear smooth with the crosshead shoes.
If the fly-wheel is in the least loose it will also cause knocking,
and it will puzzle you not a little to locate it. It may appear to be
tight; but if the key is the least bit too narrow for the groove in the
shaft, it will cause an engine to bump horribly, very much as too much
“lead” will.
LEAD.
We have already explained what “lead” is. It is opening of the port at
either end of the steam cylinder allowed by the valve when the engine
is on a dead centre. To find out what the lead is, the cover of the
steam chest must be taken off, and the engine placed at each dead
centre in succession. If the lead is greater at one end than it is at
the other, the valve must be adjusted to equalize it. As a rule the
engine is adjusted with a suitable amount of lead if it is equalized.
The correct amount of lead varies with the engine and with the port
opening. If the port opening is long and narrow, the lead should
obviously be less than if the port is short and wide.
If the lead is insufficient, there will not be enough steam let into
the cylinder for cushion, and the engine will knock. If there is too
much lead the speed of the engine will be lessened, and it will not do
the work it ought. To adjust the lead _de novo_ is by no means an easy
task.
HOW TO SET A SIMPLE VALVE.
In order to set a valve the engine must be brought to a dead centre.
This cannot be done accurately by the eye. An old engineer[5] gives
the following directions for finding the dead centre accurately. Says
he: “First provide yourself with a ‘tram.’ This is a rod of one-fourth
inch iron about eighteen inches long, with two inches at one end bent
over to a sharp angle. Sharpen both ends to a point. Fasten a block of
hard wood somewhere near the face of the fly-wheel, so that when the
straight end of your tram is placed at a definite point in the block,
the hooked end will reach the crown of the fly-wheel. The block must be
held firmly in its place, and the tram must always touch it at exactly
the same point.
Footnote 5: J. H. Maggard.
“You are now ready to set about finding the dead centre. In doing this,
remember to turn the fly-wheel always in the same direction.
“Bring the engine over till it nearly reaches one of the dead centres,
but not quite. Make a distinct mark across the cross-head and guides.
Also go around to the flywheel, and placing the straight end of the
tram at the selected point on the block of wood, make a mark across the
crown or centre of face of the fly-wheel. Now turn your engine past the
centre, and on to a point at which the mark on the cross head will once
more exactly correspond with the line on the guides, making a single
straight line. Once more place the tram as before and make another mark
across the crown of the fly-wheel. By use of dividers, find the exact
centre between the two marks made on the fly-wheel, and mark this point
distinctly with a centre punch. Now bring the fly-wheel to the point
where the tram, set with its straight end at the required point on the
block of wood, will touch this point with the hooked end, and you will
have one of the dead centres.
“Turn the engine over and proceed in the same way to find the other
dead centre.”
Now, setting the engine on one of the dead centres, remove the cover of
the steam chest and proceed to set your valve.
Assuming that the engine maker gave the valve the proper amount of lead
in the first place, you can proceed on the theory that it is merely
necessary to equalize the lead at both ends. Assume some convenient
lead, as one-sixteenth of an inch, and set the valve to that. Then
turn the engine over and see if the lead at the other end is the same.
If it is the same, you have set the valve correctly. If it is less at
the other end, you may conclude that the lead at both ends should be
less than one-sixteenth of an inch, and must proceed to equalize it.
This you can do by fitting into the open space a little wedge of wood,
changing the valve a little until the wedge goes in to just the same
distance at each end. Then you may know that the lead at one end is the
same as at the other end. You can mark the wedge for forcing it against
the metal, or mark it against the seat of the valve with a pencil.
The valve is set by loosening the set screws that hold the eccentric on
the shaft. When these are loosened up the valve may be moved freely.
When it is correctly set the screws should be tightened, and the
relative position of the eccentric on the shaft may be permanently
marked by setting a cold chisel so that it will cut into the shaft
and the eccentric at the same time and giving it a smart blow with
the hammer, so as to make a mark on both the eccentric and the shaft.
Should your eccentric slip at any time in the future, you can set your
valve by simply bringing the mark on the eccentric so that it will
correspond with the mark on the shaft. Many engines have such a mark
made when built, to facilitate setting a valve should the eccentric
become loose.
These directions apply only to setting the valve of a single eccentric
engine.
HOW TO SET A VALVE ON A DOUBLE ECCENTRIC ENGINE.
In setting a valve on a reversible or double eccentric engine, the link
may cause confusion, and you may be trying to set the valve to run one
way when the engine is set to run the other.
The valve on such an engine is exactly the same as on a single
eccentric engine. Set the reverse lever for the engine to go forward.
Then set the valve exactly as with a single eccentric engine. When
you have done so, tighten the eccentric screws so that they will hold
temporarily, and set the reverse lever for the engine to go backward.
Then put the engine on dead centres and see if the valve is all right
at both ends. If it is, you may assume that it is correctly set, and
tighten eccentric screws, marking both eccentrics as before.
As we have said, most engines are marked in the factory, so that it is
not a difficult matter to set the valves, it being necessary only to
bring the eccentric around so that the mark on it will correspond with
the mark on the shaft.
You can easily tell whether the lead is the same at both ends by
listening to the exhaust. If it is longer at one end than the other,
the valve is not properly set.
SLIPPING OF THE ECCENTRIC OR VALVE.
If the eccentric slips the least bit it may cause the engine to stop,
or to act very queerly. Therefore the marks on the shaft and on the
eccentric should be watched closely, and of course all grease and dirt
should be kept wiped off, so that they can be seen easily. Then the jam
nuts should be tightened up a little from time to time.
If the engine seems to act strangely, and yet the eccentrics are all
right, look at the valve in the steam chest. If the valve stem has
worked loose from the valve, trouble will be caused. It may be held in
place by a nut, and the nut may work off; or the valve may be held by
a clamp and pin, and the pin may work loose. Either will cause loss of
motion, and perhaps a sudden stopping of the engine.
USE OF THE CYLINDER STEAM COCKS.
It is a comparatively simple matter to test a steam cylinder by use
of the cylinder cocks. To do this, open both cocks, place the engine
on the forward center, and turn on a little steam. If the steam blows
out at the forward cock, we may judge that our lead is all right. Now
turn the engine to the back center and let on the steam. It should blow
out the same at the back cock. A little training of the ear will show
whether the escape of steam is the same at both ends. Then reverse the
engine, set it on each center successfully, and notice whether the
steam blows out from one cock at a time and in the same degree of force.
If the steam blows out of both cocks at the same time, or out of one
cock on one center, but not out of the other cock on its corresponding
center, we may know something is wrong. The valve does not work
properly.
We will first look at the eccentrics and see that they are all right.
If they are, we must open the steam chest, first turning off all steam.
Probably we shall find that the valve is loose on the valve rod, if our
trouble was that the steam blew out of the cock but did not out of the
other when the engine was on the opposite center.
If our trouble was that steam blew out of both cocks at the same time,
we may conclude either that the cylinder rings leak or else the valve
has cut its seat. It will be a little difficult to tell which at first
sight. In any case it is a bad thing, for it means loss of power and
waste of steam and fuel. To tell just where the trouble is you must
take off the cylinder head, after setting the engine on the forward
center. Let in a little steam from the throttle. If it blows through
around the rings, the trouble is with them; but if it blows through the
valve port, the trouble is with the valve and valve seat.
If the rings leak you must get a new set if they are of the
self-adjusting type. But if they are of the spring or adjusting type
you can set them out yourself; but few engines now use the latter kind
of rings, so a new pair will probably be required.
If the trouble is in the valve and valve seat, you should take the
valve out and have the seat planed down, and the valve fitted to the
seat. This should always be done by a skilled mechanic fully equipped
for such work, as a novice is almost sure to make bad work of it. The
valve seat and valve must be scraped down by the use of a flat piece
of very hard steel, an eighth of an inch thick and about 3 by 4 inches
in size. The scraping edge must be absolutely straight. It will be a
slow and tedious process, and a little too much scraping on one side or
the other will prevent a perfect fit. Both valve and valve seat must
be scraped equally. Novices sometimes try to reseat a valve by the use
of emery. This is very dangerous and is sure to ruin the valve, as it
works into the pores of the iron and causes cutting.
LUBRICATION.
A knowledge of the difference between good oil and poor oil, and of how
to use oil and grease, is a prime essential for an engineer.
First let us give a little attention to the theory of lubrication. The
oil or grease should form a lining between the journal and its pin or
shaft. It is in the nature of a slight and frictionless cushion at all
points where the two pieces of metal meet.
Now if oil is to keep its place between the bearing and the shaft or
pin it must stick tight to both pieces of metal, and the tighter the
better. If the oil is light the forces at work on the bearings will
force the oil away and bring the metals together. As soon as they come
together they begin to wear on each other, and sometimes the wear is
very rapid. This is called “cutting.” If a little sand or grit gets
into the bearing, that will help the cutting wonderfully, and more
especially if there is no grease there.
For instance, gasoline and kerosene are oils, but they are so light
they will not stick to a journal, and so are valueless for lubricating.
Good lubricating oil will cost a little more than cheap oil which has
been mixed with worthless oils to increase its bulk without increasing
its cost. The higher priced oil will really cost less in the end,
because there is a larger percentage of it which will do service. A
good engineer will have it in his contract that he is to be furnished
with good oil.
Now an engine requires two different kinds of oil, one for the
bearings, such as the crank, pin, the cross-head and journals, and
quite a different kind for lubricating the steam cylinder.
It is extremely important that the steam cylinder should be well
lubricated; and this cannot be done direct. The oil must be carried
into the valve and cylinder with steam. The heat of the steam,
moreover, ranging from about 320 degrees Fahr. for 90 lbs. pressure to
350 degrees for 125 lbs. of pressure, will quickly destroy the efficacy
of a poor oil, and a good cylinder oil must be one that will stick to
the cylinder and valve seat under this high temperature. It must have
staying qualities.
The link reverse is one of the best for its purpose; but it requires a
good quality of oil on the valve for it to work well. If the valve gets
a little dry, or the poor oil used does not serve its purpose properly,
the link will begin to jump and pound. This is a reason why makers are
substituting other kinds of reverse gear in many ways not as good, but
not open to this objection. If a link reverse begins to pound when you
are using good oil, and the oiler is working properly, you may be sure
something is the matter with the valve or the gear.
A good engineer will train his ear so that he will detect by simply
listening at the cylinder whether everything is working exactly as it
ought. For example, the exhaust at each end of the cylinder, which you
can hear distinctly, should be the same and equal. If the exhaust at
one end is less than it is at the other, you may know that one end of
the cylinder is doing more work than the other. And also any little
looseness or lack of oil will signify itself by the peculiar sound it
will cause.
While the cylinder requires cylinder oil, the crank, cross-head and
journals require engine oil, or hard grease. The use of hard grease is
rapidly increasing, and it is highly to be recommended. With a good
automatic spring grease cup hard grease will be far less likely to let
the bearings heat than common oil will. At the same time it will be
much easier to keep an engine clean if hard grease is used.
An old engineer[6] gives the following directions for fitting a grease
cup on a box not previously arranged for one: “Remove the journal,
take a gouge and cut a clean groove across the box, starting at one
corner, about one-eighth of an inch from the point of the box, and
cut diagonally across, coming out at the opposite corner on the other
end of the box. Then start at the opposite corner and run through as
before, crossing the first groove in the center of the box. Groove both
halves of the box the same, being careful not to cut out at either
end, as this will allow the grease to escape from the box and cause
unnecessary waste. The shimming or packing in the box should be cut so
as to touch the journal at both ends of the box, but not in the center
or between these two points. So when the top box is brought down tight
this will form another reservoir for the grease. If the box is not
tapped directly in the center for the cup, it will be necessary to cut
another groove from where it is tapped into the grooves already made.
A box prepared in this way and carefully polished inside, will require
little attention if you use good grease.”
Footnote 6: J. H. Maggard.
A HOT BOX.
When a box heats in the least degree, it is a sign that for lack of oil
or for some other reason the metals are wearing together.
The first thing to do, of course, is to see that the box is supplied
with plenty of good oil or grease.
If this does not cause the box to cool off, take it apart and clean it
thoroughly. Then coat the journal with white lead mixed with good oil.
Great care should be exercised to keep all dirt or grit out of your can
of lead and away from the bearing.
Replace the oil or grease cup, and the box will soon cool down.
THE FRICTION CLUTCH.
Nearly all traction engines are now provided with the friction clutch
for engaging the engine with the propelling gear. The clutch is usually
provided with wooden shoes, which are adjustable as they wear; and the
clutch is thrown on by a lever, conveniently placed.
[Illustration: A. W. STEVENS CO. FRICTION CLUTCH.]
Before running an engine, you must make sure that the clutch shoes are
properly adjusted. Great care must be taken to be sure that both shoes
will come in contact with the friction wheel at the same instant; for
if one shoe touches the wheel before the other the clutch will probably
slip.
The shoes should be so set as to make it a trifle difficult to draw the
lever clear back.
To regulate the shoes on the Rumely engine, for example, first throw
the friction in. The nut on the top of the toggle connecting the sleeve
of the friction with the shoe must then be loosened, and the nut below
the shoe tightened up, forcing the shoe toward the wheel. Both shoes
should be carefully adjusted so that they will engage the band wheel
equally and at exactly the same time.
To use the friction clutch, first start the engine, throwing the
throttle gradually wide open. When the engine is running at its usual
speed, slowly bring up the clutch until the gearing is fully engaged,
letting the engine start slowly and smoothly, without any jar.
Traction engines having the friction clutch are also provided with a
pin for securing a rigid connection, to be used in cases of necessity,
as when the clutch gets broken or something about it gives out, or you
have difficulty in making it hold when climbing hills. This pin is a
simple round or square pin that can be placed through a hole in one of
the spokes of the band wheel until it comes into a similar opening in
the friction wheel. When the pin is taken out, so as to disconnect the
wheels, it must be entirely removed, not left sticking in the hole, as
it is liable to catch in some other part of the machinery.
[Illustration: AULTMAN & TAYLOR FRICTION CLUTCH.]
MISCELLANEOUS SUGGESTIONS.
Be careful not to open the throttle valve too quickly, or you may throw
off the driving belt. You may also stir up the water and cause it to
pass over with the steam, starting what is called “priming.”
Always open your cylinder cocks when you stop, to make sure all water
has been drained out of the cylinder; and see that they are open when
you start, of course closing them as soon as the steam is let in.
When you pull out the ashes always have a pail of water ready, for you
may start a fire that will do no end of damage.
If the water in your boiler gets low and you are waiting for the tank
to come up, don’t think you “can keep on a little longer,” but stop
your engine at once. It is better to lose a little time than run the
risk of an explosion that will ruin your reputation as an engineer and
cause your employer a heavy expense.
Never start the pump when the water in the boiler is low.
Be sure the exhaust nozzle does not get limed up, and be sure the pipe
where the water enters the boiler from the heater is not limed up, or
you may split a heater pipe or knock out a check valve.
Never leave your engine in cold weather without draining off all the
water; and always cover up your engine when you leave it.
Never disconnect the engine with a leaky throttle.
Keep the steam pressure steady, not varying more than 10 to 15 lbs.
If called on to run an old boiler, have it thoroughly tested before you
touch it.
Always close your damper before pulling through a stack yard.
Examine every bridge before you pull on to it.
Do not stop going down a steep grade.