Rough and Tumble Engineering

by James H. Maggard

Any young engineer who will make use of what he has read will never get his engine into much trouble. Manufacturers of farm engines to-day make a specialty of this class of goods, as they endeavor to build them as simple and of as few parts as possible. They do this well knowing that, as a rule, they must be run by men who cannot take a course in practical engineering. If each one of the many thousands of engines that are turned out every year had to have a practical engineer to run it, it would be better to be an engineer than to own the engine; and manufacturers knowing this, they therefore make their engines as simple and with as little liability to get out of order as possible. The simplest form of an engine, however, requires of the operator a certain amount of brains and a willingness to do that which he knows should be done; and if you will follow the instructions you have already received, you can run your engine as successfully as any one can wish as long as your engine is in order, and, as I have just stated, it is not liable to get out of order, except from constant wear, and this wear will appear in the boxes, journals and valve. The brasses on wrist pin and cross-head will probably require your first and most careful attention, and of these two the wrist or crank box will require the most; and what is true of one is true of both boxes. It is, therefore, not necessary to take up both boxes in instructing you how to handle them. We will take up the box most likely to require your attention. This is the wrist box. You will find this box in two parts or halves. In a new engine you will find that these two halves do not meet on the wrist pin by at least one-eighth of an inch. They are brought up to the pin by means of a wedge-shaped key. (I am speaking now of the most common form of wrist boxes. If your engine should not have this key, it will have something which serves the same purpose.) As the brasses wear you can take up this wear by forcing the key down, which brings the two halves nearer together. You can continue to gradually take up this wear until you have brought them together. You will then see that it is necessary to do something, in order to take up any more wear, and this "something" is to take out the brasses and file about one-sixteenth of an inch off of each brass. This will allow you another eighth of an inch to take up in wear.

Now here is a nice little problem for you to solve and I want you to solve it to your own satisfaction, and when you do, you will thoroughly understand it, and to understand it is to never allow it to get you into trouble. We started out by saying that in a new engine you would most likely find about one-eighth of an inch between the brasses, and we said you would finally get these brasses, or halves together, and would have to take them out and file them. Now we have taken up one-eighth of an inch and the result is, we have lengthened our pitman just one-sixteenth of an inch; or in other words, the center of wrist pin and the center of cross-head are just one-sixteenth of an inch further apart than they were before any wear had taken place, and the piston head has one-sixteenth of an inch more clearance at one end, and one-sixteenth of an inch less at the other end than it had before. Now if we take out the boxes and file them so we have, another eighth of an inch, by the time we have taken up this wear, we will then have this distance doubled, and we will soon have the piston head striking the end of the cylinder, and besides, the engine will not run as smooth as it did. Half of the wear comes off of each half, and the half next to the key is brought up to the wrist pin because of the tapering key, while the outside half remains in one place. You must therefore place back of this half a thin piece of sheet copper, or a piece of tin will do. Now suppose our boxes had one-eighth of an inch for wear. When we have taken up this much we must put in one-sixteenth of an inch backing (as it is called), for we have reduced the outside half by just that amount. We have also reduced the front half the same, but as we have said, the tapering key brings this half up to its place.

Now we think we have made this clear enough and we will leave this and go back to the key again. You must remember that we stated that the key was tapering or a wedged shape, and as a wedge, is equally as powerful as a screw, and you must bear in mind that a slight tap will bring these two boxes up tight against the wrist pin. Young engineers experience more trouble with this box than with any other part of the engine, and all because they do not know how to manage it. You should be very careful not to get your box too tight, and don't imagine that every time there is a little knock about your engine that you can stop it by driving the key down a little more. This is a great mistake that many, and even old engineers make. I at one time seen a wrist pin and boxes ruined by the engineer trying to stop a knock that came from a loose fly-wheel. It is a fact, and one that has never been satisfactorily explained, that a knock coming from almost any part of an engine will appear to be in the wrist. So bear this in mind and don't allow yourself to be deceived in this way, and never try to stop a knock until you have first located the trouble beyond a doubt.

When it becomes necessary to key up your brasses, you will find it a good safe way to loosen up the set screw which holds the key, then drive it down till you are satisfied you have it tight. Then drive it back again and then with your fist drive the key down as far as you can. You may consider this a peculiar kind of a hammer, but your boxes will rarely ever heat after being keyed in this manner.

KNOCK IN ENGINES

What makes an engine knock or pound? A loose pillow block box is a good "knocker." The pillow block is a box next crank or disc wheel. This box is usually fitted with set bolts and jam nuts. You must also be careful not to set this up too tight, remembering always that a box when too tight begins to heat and this expands the journal, causing greater friction. A slight turn of a set bolt one way or the other may be sufficient to cool a box that may be running hot, or to heat one that may be running cool. A hot box from neglect of oiling can be cooled by supplying oil, provided it has not already commenced to cut. If it shows any sign of cutting, the only safe way is to remove the box and clean it thoroughly.

Loose eccentric yokes will make a knock in an engine, and it may appear to be in the wrist. You will find packing between the two halves of the yoke. Take out a thin sheet of this packing, but don't take out too much, as you are liable then to get them too tight and they may stick and cause your eccentrics to slip. We will have more to say about the slipping of the eccentrics.

The piston rod loose in cross-head will make a knock, which also appears in the wrist, but it is not there. Tighten the piston and you will stop it. The piston rod may be keyed in cross head, or it may be held in place by a nut. The key is less liable to get loose, but should it work loose a few times it may be necessary to replace it with a new one. And this is one of the things that cause a bad break when it works out or gets loose. If it gets loose it may not come out, but it will not stand the strain very long in this condition, and will break, allowing the piston to come out of cross head, and you are certain to knock out one cylinder head and possibly both of them. The nut will do the same thing if allowed to come off. So this is one of the connections that will claim your attention once in a while, but if you train your ear to detect any unusual noise you will discover it as soon as it gives the least in either key or nut.

The cross-head loose in the guides will make it knock. If the cross-head is not provided for taking up this wear, you can take off the guides and file them enough to allow them to come up to the cross-head, but it is much better to have them planed off, which insures the guides coming up square against the cross-head and thus prevent any heating or cutting.

A loose fly-wheel will most likely puzzle you more than anything else to find the knock. So remember this. The wheel may apparently be tight, but should the key be the least bit narrow for the groove in shaft, it will make your engine bump very similar to that caused by too much or too little "lead."