(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.
Fig. 54.—Suggested Method of Polishing Cylinder Walls of Cast-iron Cylinder Block after it has been Preheated.
Fig. 55.—Cast-iron Cylinder Block with Part Broken Off.
Fig. 56.—Showing how Broken Part on Cast-iron Block should be Lined up before Welding. Position Greatly Exaggerated.