CHAPTER VI

PART ONE.--WELDING OF CAST IRON

(=66=) In order to know how to weld, it is quite imperative that the operator first know the kind of metal he is to work on. It is surprising to find how few welders know their metals thoroughly. An incident might be cited where some welders depend upon the sparks given off by the emery wheel in determining the kind of metal they are about to weld. They will approach the wheel; grind off their work, noting the sparks; return to their welding table; choose their filler rods and do their welding without any delay whatsoever, much to the consternation of their fellow workers. There are four simple ways in common use to distinguish between cast iron, malleable iron, and steel; they are: By the cross-section of a fresh break, by application of the welding torch, by the sparks given off when applied to the emery wheel and by the chisel test.

[Illustration: FIG. 42.--Characteristic Sparks of Different Irons and Steels Thrown off by an Emery Wheel. Wheel should be Clean Cutting and Run about 7000 Feet per Minute.

(1) Shows cast iron. No sparks unless impurities are present.

(2) Is wrought iron almost free from carbon. Heated particles thrown from wheel follow straight line. These become broader and more luminous some distance from their source of heat.

(3) Illustrates mild steel action. Small amount of carbon present causes a division or forking of the luminous streak.

(4) Shows the effect of increasing the carbon from 0.50 to 0.85 per cent in mild steel. The iron spark lines diminish: the forking of the luminous streak occurs more frequently, being subdivided by re-explosions from smaller particles.

(5) Is a piece of carbon tool steel. The iron lines are practically eliminated with the increase of the explosions and subdivisions, causing display of figures.

(6) Gives the spark of high-speed steel, containing in addition to 65 per cent carbon, other alloying elements, chiefly tungsten and chromium.

(7) Represents a manganese spark. (Occasionally found in cast iron.)

(8) Shows spark thrown from old grade of “Mushett” steel.

(9) Represents a magnet steel spark.]

(=67=) Externally cast iron usually has some sand on its surface and its cross-section shows the grain to be fine, even, and to have a dull grayish color. The surface of malleable iron contains no sand and its grain is very fine, such as cast iron, but slightly darker in color. A very fine steel veneer is on all surfaces of malleable iron, which is much lighter in color. When the welding torch is applied to cast iron, no sparks are given off, but when applied to malleable iron a bright spark is thrown off which breaks in falling, showing that the outside material is steel. These sparks soon cease and the metal which is molten is covered by a heavy oxide or skin which recedes or draws away from the flame slightly, showing a very porous cast-iron interior. When brought in contact with the emery wheel steel sparks, which are very luminous and break in falling, are given off first in the case of malleable iron, but they soon change to the dull red spark of cast iron. When a chisel is applied to cast iron, the iron chips off; when applied to malleable iron the edge will curl up, then chip off when the cast iron is reached. The cross-section of cast steel shows a bright, coarse, silvery gray grain. When the torch is applied a distinctively steel spark which is luminous and breaks in falling is thrown off. When applied to the emery wheel steel sparks are thrown off; when the edge is chipped by a chisel it will curl up.

[Illustration: METHODS OF DISTINGUISHING METALS

Here are five methods, any one or all of which may be used to learn the nature of common castings which might confuse the welder.

---+-----------+--------------------+-----------------+--------------- No.| Test. | Malleable Iron. | Cast Steel. | Cast Iron. ---+-----------+--------------------+-----------------+--------------- 1 |Outside |Generally smooth and|Rough surface |Surface fairly |Appearance.|free from all sand, |with sand in |smooth but | |weighs about same |evidence, weighs |generally shows | |as cast iron. |much more |some sand. | | |than cast iron. | ---+-----------+--------------------+-----------------+--------------- 2 |Cross- |Ring of bright steel|Large, bright, |Fine, uniform, |section |crystals outside, |luminous, silver |dark gray, |Test. |with darker iron |crystals. |crystals. | |crystals inside. | | ---+-----------+--------------------+-----------------+--------------- 3 |Emery Wheel|Few steel sparks and|Bright, luminous |Dull red sparks |Test. |then iron sparks |sparks that |that do not | |from interior. |break in falling.|break. ---+-----------+--------------------+-----------------+--------------- 4 |Chisel |Surface will curl |Will curl before |Will chip off. |Test. |and interior break |breaking. | | |off. | | ---+-----------+--------------------+-----------------+--------------- 5 |Torch Test.|Gives way before |Gives forth |Gives no sparks | |flame and delivers |bright sparks |except where | |few sparks. Metal |that break in |there are | |becomes porous. |falling. |impurities. ---+-----------+--------------------+-----------------+---------------

FIG. 43.]

(=68=) The metal in the filler-rod should be the same in practically all cases as the metal to be welded. There are few exceptions to this rule, but the principal one is that of malleable iron. The cast iron in the rods is of a very good grade and generally much better than the piece to be worked upon. To permit the ready flow of the rod and eliminate oxidation, as much as possible, three per cent of silica is generally used in the casting of filler-rods for cast iron welding. Piston rings and other scrap iron should not be used for filler-rods, as they contain many impurities such as core-sand, dirt, grease, etc., which will ruin the weld. It is disheartening to see some operators attempt to economize on the filler-rod. It is not an uncommon sight to see several dollars’ worth of gas and the same amount of the welder’s time, together with a few cents’ worth of filler rods all lost, and the operator’s reputation ruined. This, because an attempt is made to save the few cents involved in the filler-rods by substituting a rod of a very poor grade.

(=69=) A flux is not used, as many suppose, to cement the filler-rod to the metal. It is used purely as a cleansing agent and may be likened to the acid used in soldering. It does not act on the metal until the latter has reached the melting-point, but then it starts to break up the oxides and clean the surface. This action permits the metal to flow together more readily. A cast-iron flux is always used in welding cast iron, to break up the oxide, because the cast iron itself will melt before the oxide and no matter how hot the metal is it will not flow together as long as this oxide is present.

(=70=) To obtain the best results, reliable fluxes should always be used. Occasionally an accident will happen to the flux can, when the operator is on some isolated job and a substitute flux must be obtained at once. Equal parts of bicarbonate of soda (cooking soda), and carbonate of soda (ordinary washing soda), may be purchased from any grocery in the powdered form and mixed together thoroughly. This will tide the welder over until he can return to the shop and replenish his supply.

[Illustration: FIG. 44.--Whenever Possible, the Beginner should “V” His Work, and Complete His Weld from One Side only. On heavy work, however, it will be necessary to “V” out from both sides, as is here shown.]

(=71=) The flux is generally applied by means of the filler-rod. One end is heated and dipped in the flux; enough will adhere to break up part of the oxides, on the ordinary-sized job. The flux is carried to the work, which should be at the melting-point and introduced between the flame and the metal. Oxides will break up immediately and the metal will flow together, but it must be remembered that the flux has no action on cold or moderately heated metals. The flux as has been explained is used to clean the metal and break up the oxides. To the oft-repeated question, how often should the flux be applied, answer is made as follows: As often as it is necessary to clean up the metal and break up the oxides. All fluxes should be kept in airtight containers when not in use, to keep their chemical contents in the very best condition and it is best to use only a small quantity of flux on the welding table at one time.

(=72=) Oxy-acetylene welding is purely a fusing process and the most important points to remember in executing a weld are, to eliminate the entire crack in the fracture and to add the filler-rod without changing the character of the metal. On thin pieces of metal it is possible to depend upon the force of the flame to entirely penetrate to the depth of the crack but on work three-eighths of an inch thick or over, it is well to “V” out or remove some of the surface metal around the crack in order to get down to the bottom. By “V-ing” we mean to chip or grind off each edge at an angle of approximately 45 degrees, so that the opening will form an angle of 90 degrees where the two pieces come together, with the crack at the bottom portion of the “V.” This should NOT be ground down to a knife edge, for it will readily burn up. It is preferable to leave about one-eighth inch along the line in order that the pieces will fit together and the proper alignment may be obtained. If two pieces of cast iron have been prepared in this manner the neutral flame of the welding torch is brought down in such a manner that the tip of the cone just licks the metal. The heat is not applied directly to the line of weld to start with, but rather to the surrounding part. This is done in order to get the entire locality in a condition which will not withdraw too much of the heat from the line of the weld, once the fusing is begun. If it is found that the tip will not produce enough heat to bring the metal to a red heat in a fairly short time, a larger tip should be used.

[Illustration: FIG. 45.--Starting a Cast-iron Weld.]

[Illustration: FIG. 46.--Reinforcing a Cast-iron Weld.]

(=73=) No set rule can be given as to the sized tip to be used on various kinds of metal. It will largely depend upon the welder’s ability and judgment. When the metal is brought to red-heat, the neutral flame or cone is brought into contact with the lowest portion of the “V” and held there until it is seen that the metal is melted on both sides. The filler-rod, which has previously been heated at one end and dipped into the flux so that an amount adheres to the end of the rod, then carries this flux to that portion of the weld which is under way. Enough flux is blown off the rod into the weld to clean up the surface and permit the metal flowing together. The crack should be melted together all along before any additional metal is added, for the elimination of the crack is extremely important. It might be noted that as soon as the metal begins to flow freely the neutral flame should be raised a short distance from the work in order to better control the molten metal. In order to build up the metal to the original state along the line of weld or perhaps reinforce it, the sides and bottom of this “V-ed” out part are then brought to a molten state and held there while the filler-rod which brings up more flux is stirred into this metal and the end melted off. In this way the flame does not come in direct contact with the filler-rod and is used only to keep the metal in a molten condition. As much of the filler-rod can be melted off as is thought necessary to bring the weld to the normal condition of the metal or an additional reinforcement can be built up, if it is thought advisable. If care is taken in the above procedure, many of the blow holes and hard spots in the weld will be eliminated, for any impurities that might gather will be displaced by the melted metal and will float to the top. In cooling a weld of this kind, care should be taken not to permit any sudden chilling for this will tend to harden the weld. It is best to cool it slowly by burying it in slack lime, ashes, or wrap it with asbestos paper to keep the air from it as much as possible.

[Illustration: FIG. 47.--This Problem does not Require Preheating to Care for Contraction, as the Ends of _A_ and _B_ are not Confined.]

(=74=) There may be a great many causes for blow holes and hard spots in the weld, but probably they can all be traced directly to the lack of heat. It must be remembered that welding is a fusing process and heat is absolutely essential. Therefore it should not be used sparingly. The application of heat always causes expansion. There are no exceptions to this rule, likewise upon cooling the metal there will be a contraction. Outside of the actual welding, that is, the fusing of the metal into a homogeneous mass, perhaps the greatest problem that the welder has to confront is the expansion and contraction of his metals. Whenever the ends of two pieces of metal which are to be welded are free to move, or even one end, there will be no difficulty encountered with contraction and expansion, but if these ends are confined, it is an entirely different problem.

[Illustration: FIG. 48.--Preheating Problem. Ends of Bars _A′_ and _B′_ are Confined.]

(=75=) To illustrate this point more clearly, the following very simple example will be given. In Fig. 47 we have two bars of metal _A_ and _B_ which have been beveled off or “V-ed” out as shown at the point _C_. Now as soon as the heat is introduced at _C_ there is bound to be an expansion of the metal at that point. Naturally if the pieces were heated slowly and for a considerable distance, the cool ends of these bars would be forced outward. We will assume that the heat is introduced very rapidly and the metal is brought to a molten state; that instead of the contraction forcing the cool ends outward, whatever expansion there is, is taken care of, at the weld, for the metal when melted will readily push together. It is also assumed that the bars are heavy enough to overcome what slight force might be in evidence from the expansion. A weld is then made and allowed to cool. As it cools, there is bound to be a contraction along the line of the weld and the welded piece will be slightly shorter than the work before the weld, for it will draw in the pieces _A_ and _B_. As can be seen, there is no particular force preventing the contraction of such a weld for the ends are free to move. However, let us turn to Fig. 48, which constitutes an entirely different problem. It might seem that the ends _A′_ and _B′_ appear the same as _A_ and _B_ in Fig. 47, but such is not the case. The ends farthest from the weld are confined, held in place by a heavy frame which does not permit their free movement. When heat is introduced at the point of welding _C′_, about the same action takes place as in the previous problem, but as soon as the weld commences to cool let us see what happens. The bar _A′B′_ must be shortened so there is an inward pull on the bars _D′_ and _E′_. If this work were cast iron or aluminum it would certainly be broken by the strains set to working and would naturally break at _C′_, where the metal is still hot. If it were steel or one of the ductile metals, it might twist and warp in its endeavor to overcome these internal strains. This illustrates in a very simple manner the difference between what is known as a “cold” and a “preheating” job. In the first no provision is made for expansion and contraction. In the second means are taken to overcome these important factors. In order to provide for the successful welding of the second problem, it is only necessary to heat up the bars _X_ and _Y_ about the same distance as the center will be heated, and keep them in that condition while executing the weld at _C′_, then allowing the whole to cool gradually.

PART TWO.--WELDING OF CAST IRON

(=76=) Before commencing to weld, or even turning on the gas, it is well to see that all preparations have been made and all materials on hand to bring the weld or whatever job it may be, to a finished state.

[Illustration:

(_Courtesy of Ben K. Smith, U. S. Welding Co._)

FIG. 49.--This Locomotive Cylinder was Welded at the Saddle, near the Frame.]

(=77=) As a specific example of a simple welding operation let us consider that two cast-iron bars, measuring one by six inches and twenty-four inches long are to be welded end to end. To start with it would be necessary to “V” off the ends that were to be joined at an angle of about 45 degrees, leaving about one-eighth inch along the bottom edge to line the metals up with and to see whether they are in proper position. If the bar were to measure exactly forty-eight inches when finished it would be necessary to move these bars apart about one-sixteenth of an inch in order to provide for their contraction. It is assumed that the weight of the bars would be sufficient to prevent their pushing apart when the line of the weld is brought to a molten state and that the expansion will be taken care of within the weld. The bars after being lined up are ready for welding, but there are such things as filler-rods, flux and goggles that are necessary to have on hand before starting to work. It is well to have a few fire bricks, a little asbestos paper and a bucket of water convenient, in case these things are needed. The acetylene gas should then be turned on and ignited. A sufficient pressure should be passing through the regulator, when using a medium, or high-pressure apparatus, to cause the flame to leave the torch tip about twice the distance of the diameter of the orifice of that particular tip. Then turn on the oxygen until a neutral flame is obtained. On some torches it is necessary to make a second adjustment by turning on a little more acetylene gas and still more oxygen, until a goodly sized neutral flame results. Apply the flame to the pieces, so that the neutral flame will just lick the surface of the metal. Move the torch slowly forward and backward on each side of the “V” until the two edges are a dull red color, or better still a bright cherry red, then hold the torch stationary until the metal in the “V” nearest to the operator commences to melt. Then bring the filler-rod end in contact with the flame to get it heated and plunge it into the flux which should be near at hand. Enough flux will adhere to break up the oxides and by placing the rod between the flame and the metal, enough flux will be introduced to allow fusing of the metal. Proceed in this manner until the metal in the bottom of the “V” is properly fused throughout its length. Do not add the filler-rod, up to this point unless necessary. In holding the flame, see that the preheating flame will heat the parts yet to be welded. The weld should be made away from the operator. After the metals along the bottom have united and a good foundation has been obtained, then start the weld at the beginning once more, working the flame across the piece, in the same manner as before; bringing the metal to the molten state and stirring the filler-rod in it. As the filler-rod melts, the amount of molten metal naturally increases and the flame is moved along the weld as fast as the metal is added. It is important that the metal is in a molten condition. It is almost impossible to get too much heat on this type of work. Build up the weld slightly higher than the original piece. It may be found in finishing up the corners that the velocity of the gases or the force of the flame will be sufficient to blow the melted metal away. This may be overcome by directing the flame at a different angle, and will cause no difficulty after a little practice. Trouble, too, may be experienced on thin cast-iron sections by having the metal collapse through the force of the flame, but this can be remedied in the same manner. While the weld is still in a heated condition, it is possible to finish it by scraping the surplus metal off with the side of the filler-rod, the chill of which has been taken off before it is allowed to come in contact with the molten metal. Another popular method that will produce even better results is to use a very heavy rasp file to bring the weld down to the measurements desired. During all of the previous operations the flame never leaves the line of weld. When the weld is completed, the torch is shut down by turning off the oxygen first, and then the acetylene, and the welded bar is covered up to prevent its cooling too rapidly.

PART THREE.--WELDING OF CAST IRON

(=78=) Problems in expansion and contraction should not be difficult, if it is remembered that heat causes expansion and the withdrawal of heat, or cooling causes contraction. As previously stated, when the ends of the pieces which are being welded are free to move, there is not much danger of having contraction strains set up. Where the ends are confined, measures must be taken to overcome this. In welding large pulley wheels, for example, it may be advisable to do the job without taking time to preheat. Breaks may be in evidence at any part of the wheel and generally the ends are confined, such as in the case of a spoke. If it is borne in mind that the expansion will take care of itself, the contraction is the only consideration, in a case of this kind. The welder will see that if he can spring the edges apart a sufficient amount to provide for the spoke coming back to normal when welded, he will have no difficulty. The way to proceed in a case of this kind would be to open the rim by sawing it and then introduce a jack or some sort of a wedge between the hub and the rim. This will open the crack in the spoke the amount desired. As soon as the weld is executed and while still hot, the jack is removed to permit the rim being drawn in. Later the rim can be welded, by introducing jacks between the spokes and the same procedure followed. It always must be remembered that provision must be made for the contraction, even though it be only one thirty-second or one-sixteenth of an inch. The distance will depend entirely upon the welder, as some operators use small tips and cover a small area, while others employ larger tips and cover twice the area. It is therefore impossible to set any specific distance and each welder should try to figure this out for himself.

[Illustration:

(_Courtesy of Torchweld Equipment Co._)

FIG. 50.--Large Cast-iron Gear Wheels. Although the Face on These Gears Measured 10 Inches, New Teeth were Added by Blanking In, as Shown in the Right-hand View, and Later Machined.]

(=79=) There are many jobs not of a preheating nature that at times cause perplexity on the part of the welder. A good example of this is a cast-iron gear wheel. A number of its teeth have been broken out. Now there are three very common ways of building up or repairing such castings. First by aid of carbon blocks, cut to form and the teeth cast in by the use of the torch; second, by blanking in the space between the teeth and then sawing out the individual tooth or cutting it out with a milling machine or shaper; third, by building up each tooth with the welding rod and torch, and later dressing it down with a file. One very important point must be uppermost, when dental work on gears is being done, a good foundation is necessary, for regardless of how well the tooth may be shaped, if it is not firmly secured to the wheel itself, it will be of very little value. Another very important point is in the finishing of such gears, to see that the teeth which have been added correspond in the pitch and mesh exactly as the others do. The importance of seeing that things of this nature are machined correctly should not require mention, but it has often been found that machinists are very careless about finishing this kind of work and if anything goes wrong, the welder is naturally at fault. Therefore it is always well to put the gears which have been welded back into place and turn them over slowly by hand to see that they are in good condition before the power is turned on. In allowing this kind of work to cool after it has been welded, some operators permit it to be hurried, with the result that there may be hard spots to confront the machinist when finishing. If he ruins one or two of his cutters he will naturally frown upon all welding work. It is therefore desirable for this and many other reasons to have the weld come out as soft as possible, and great care should be exercised in cooling. Any weld that is subjected to machining, allow it to cool slowly in slack lime, in ashes, or cover it securely with asbestos paper. Occasionally it may be found difficult to find sections of carbon blocks which will take care of a job of this kind. Many welders who have had to run around the country, and do jobs in isolated places, have found that the carbon centers, from the ordinary dry cell batteries, which may be found practically everywhere in a discarded condition, can be shaped on an emery wheel and patched together in a manner that will permit their use. However, when such are used, it is quite necessary that they be heated a little with a torch beforehand, in order to drive out any chemicals or acids that may be contained in them. Unless these chemicals are removed, the molten metal coming in direct contact with them might be injured to a considerable extent.

[Illustration:

(_Courtesy of the Oxweld Acetylene Co._)

FIG. 51.--This View Shows new Teeth being Welded in an 8¹⁄₂-ft. Cast-iron Gear, Weighing over 5 Tons. Note the Improvised Preheating Oven.]

(=80=) Ofttimes there are castings upon which parts wear off in a very short time. There may be very little strain upon these parts, yet the constant wear will weaken them in time. It is well to remember the action of a carbonizing flame when executing work of this kind. Introduce an excess of acetylene when finishing up the work. It will be found that with a strongly carbonizing flame, carbon will be taken up by the molten metal and the finished weld will be considerably harder and will wear longer than if it were executed by a neutral flame. An abrupt cooling will chill the metal on the surface and make it wear longer than it would otherwise.

PART FOUR.--WELDING OF CAST IRON

[Illustration:

(_Courtesy of Ben K. Smith, U. S. Welding Co._)

FIG. 52.--View of Locomotive Cylinder with Three Jackets 3 Inches Thick. This job weighed over 16 Tons and Required Fifty-six Hours of Welding.]

[Illustration:

(_Courtesy of Torchweld Equipment Co._)

FIG. 53.--Various Types of Cylinders before and after Welding.]

(=81=) The true index as to the success of a weld will depend entirely upon the finished job. If it is usable, i.e., if it can be put back into service again and give satisfaction, it may be considered a successful weld. If a piece were to be warped, distorted, contain hard spots which could not be machined, or have internal strains, which would not make it safe for use (such as fly-wheels), it could not then be considered satisfactory and it would be only wasted energy. Perhaps one of the most common jobs in the ordinary commercial shop, and one which is the most abused, is the common cast-iron cylinder block found on the gasoline engine. This is so constructed that there are two walls of metal, very thinly cast; the innermost being the cylinder wall, and the outermost a water-jacket. The cylinder wall is machined very accurately to accommodate pistons moving at a very rapid rate, up and down and yet holding compression. The upper part of the cylinder is called the head, and generally has two or more valve seats which must be in alignment with the valve guides to make an airtight seat for the valves. Now this water-jacket is usually very thin, perhaps three-sixteenths to one-quarter inch in thickness, and when there are two, three, four, or more cylinders cast in one block, there are bound to be internal strains set up in casting within the piece itself. These strains are removed to a large extent by baking the rough casting before machining. Generally there are some strains left in every cylinder block of this nature. If the water in the water-jacket freezes or some other force comes in contact with the thin castings which constitute a block, the metal will give way at its weakest point, and the welder is usually called upon to repair it. At times these cracks are exceedingly small and the temptation is to braze or attempt to weld the small portions. However, as soon as there is heat introduced into the water-jacket and not into the cylinder wall, there are certain to be strains set up which, if sufficient, will distort the cylinder and make it useless unless it is rebored. The sooner welders realize that work of this nature must be preheated throughout, to a point as near melting as they can approach without causing the metal to scale, before any welding is attempted, the better success will be obtained in these lines. It is quite necessary to line up the work well, so that it will not sag when heated. It is best to heat very slowly and cool in the same manner to insure the best results. There are many preheating agencies, such as oil-ovens, preheating torches and the like, but about the best and most reliable agent known is charcoal, which heats up very gradually, makes a good even fire and dies down slowly which is the manner desired. Occasionally cracks will be found in the combustion head of the cylinder. It is very difficult to get the torch down inside the cylinder to execute this weld unless the operator has a special torch for this purpose. Even then it is difficult to keep the torch lighted when working over a newly made charcoal fire. For this reason, other means must be used when working on a job of this kind. First the crack is accurately located, then a piece is cut out of the water-jacket just over the crack by means of a chisel, hack-saw or drill press. Never attempt to remove a piece of this nature with the flame, for the introduction of heat may distort the piece at this time. “V” out the crack in the combustion head and scrape off as much of the brown oxide and dirt formation as possible. It is well to clean off more than needed and to even “V” out the crack a greater distance than is thought necessary. This will insure a good weld being made in one operation. The cylinder is then preheated with the crack uppermost so that welding can be executed with the least possible difficulty. While preheating is taking place it is well to tack the small section of the water-jacket which has been removed, to the end of the filler-rod, and place it too, in the preheating oven, with the end of the filler-rod projecting so that it will be available whenever needed. When the cylinder is red hot the weld should be executed; particular attention being given to see that each part of the metal is actually fused to prevent any leaks occurring later. As a rule the welder can tell when he has made a successful weld by observing the flow of his metal, and it will not be necessary for him to test out this cylinder weld before adding the water-jacket. The piece of the water-jacket is then replaced; it can be very easily handled by means of the filler-rod which has been tacked on. Weld this section securely in place and cover the piece of work with asbestos paper and permit it to cool with the dying fire. When cold, all port holes in the water-jacket should be closed and the cylinder tested for leaks. This can be done by introducing water into the water-jacket and applying about fifteen pounds of air pressure. Wet spots will appear if there are any leaks. If the cylinder is found tight it should be polished, then oiled, and the outside given a coat of filler or painted to make it presentable. Work is generally very much discolored when coming out of the fire. A simple device for polishing the cylinder bore may be made by turning out a hardwood block about three inches long and a little less in diameter than the size of the piston. This should be split as shown in Fig. 54, and wrapped with very fine emery cloth, then put into the cylinder and a wedge placed between the two halves. Spread them apart so they will come in contact with the cylinder wall on all sides. A screwdriver may be used for this purpose if necessary. By screwing this into the cylinder its full depth, with the aid of a little oil, a very highly polished surface may be obtained.

[Illustration: FIG. 54.--Suggested Method of Polishing Cylinder Walls of Cast-iron Cylinder Block after it has been Preheated.]

[Illustration: FIG. 55.--Cast-iron Cylinder Block with Part Broken Off.]

[Illustration: FIG. 56.--Showing how Broken Part on Cast-iron Block should be Lined up before Welding. Position Greatly Exaggerated.]

(=82=) Another cylinder block job that generally causes more confusion than is necessary is brought about when welding on small lugs, such as shown in Fig. 55. When welding these lugs on from the outside only, they generally warp upwards in cooling and it is either necessary to build up the bottom side of this lug or to machine off the entire face in order to have the end square. This can easily be overcome by permitting the lug to sag before welding and then dress off the small portion that continues to sag, after it is welded, rather than face off the whole surface. See Fig. 56.