American Diesel Piston and engine is, of course, no longer manufactured. However, many of these older engines are still in service, and the operator should be as interested in it as in more modern designs. The piston has a flat crown or top that is strengthened by ribs which extend down along the sides to the pin bosses, as shown in Fig. 50. The bosses are bored taper and offer support for both ends of the pin which are of different diameters. The pin is fastened into the piston by a washer and lock-nut; a dowel or short key at the large .end pre vents any turning of the pill. Since the latter is ground to a seat in the bosses, the contact is highly satisfactory.
The chief difficulty experienced with this design of piston is the distortion at the pin bosses, with a resultant oval shape. This distortion produces severe cutting on the piston sides along lines about 30 degrees from the pin axis. It is at once appar ent that the pin holds the two bosses at a fixed distance; when the piston heats, the expansion will occur along the weakest section. Figure 51 outlines the points a.a. of distortion. The pin bearing is oiled by the splash from the crank-case; consequently no oil passages are needed in the pin.
The number of rings used with this piston varies, ranging from four to seven. Frequently one of these pistons is found equipped with two rings per groove. In such event, the first step toward the elimination of ring trouble is the substitution of one broad ring in each groove.
Busch-Sulzer Type B Piston and Pin.—The type B piston represents the modern development of the Diesel piston design. The head is thick to better resist the cylinder .pressure and is concave: The clearance is small, and it has been necessary to cut away the edge of this concave to afford a clear passage for the gases as they enter or depart around the valves. To avoid distortion of the walls it is strongly reinforced by girth ribs. Seven rings are used about. the upper part for sealing; a single ring is placed at the bottom as an oil wiper.
The chief variation from the usual American design is the Water-cooling of the. head. This feature is clearly shown in Fig. 52, although the water piping is not included in the drawing.
The pipes are rigid and run parallel to the piston axis at each side of the connecting-rod. The lower ends slide in the stuffing boxes which are connected to the engine's water-piping system. This telescopic method of feeding the water is superior to the pantagraph or knuckle form. There is no inertia effect of swinging parts as with the latter type. The stuffing-box is
much easier to maintain water-tight than is the knuckle. Even the telescopic arrangement will in time give trouble from weeping. In the Busch-Sulzer the crank-case receives all the return lubricating oil. For this reason leaks at the stuffing-boxes allow water to mix with the oil returns, practically destroying the lubricating qualities of the latter. On each occasion that the engine is stopped, the crank-case doors should be opened and the water connections examined.
The piston pin is tapered at both ends and is held by a washer and nut as outlined. When the engine has been in careless hands, the pin may deform the bosses to such an extent that the pin has a poor bearing at the ends. It then becomes necessary to grind the pin to new seats. To accomplish this the dowel key at the big end must be removed to allow rotation of the pin. McIntosh & Seymour Piston and Pin.—This company followed the designs of their Swedish associates in building the piston appearing in Fig. 53.
The head is concave and is strongly reinforced on the lower side with a series of ribs. These ribs do not extend down along the piston walls, which are supported by a set of girth ribs.
The piston pin is straight and is held in the bosses by set-screws. Allis-Chalmers Piston and Pin.—The first Diesel engines manufactured by the Allis Chalmers Co. had pistons of the standard one-piece construc tion. The small clearance maintained between the piston and cylinder liner made this design impractical, and it was early replaced by the piston outlined in Fig. 54. The piston body is formed of high-grade cast iron and is provided with a false or removable head. This head is of nickel-steel, which develops fractures at a much slower rate than does cast iron, and is held in a machined recess by the stud shown. The piston head is conical in shape, and the impinge ment of the fuel charge is localized at the center of the nickel steel head. This construction enables the builder to give a very small clearance between the piston and cylinder without danger of piston seizing due to head expansion. The compres sion is sealed by six rings while an oil-wiper ring is used at the base. To avoid the trouble of lubricating oil depositing on the inner side of the piston head and forming a hard scale, a baffle plate is incorporated in the casting. This plate is in two parts which allows a circulation of air. While this plate is fairly effectual in maintaining a clean head, oil will deposit on the inner walls of the piston, as in all horizontal engines.