CYLINDERS AND CYLINDER HEADS Since the first Diesel engines followed gas engine practice as much as was possible, it is not surprising that the one-piece cylinder was incorporated in the first designs. At the present time no Diesel of any size is fitted with a cylinder having the liner cast integral with the jacket, though a few small units do use it on account of the smaller initial cost and the consequent lower replacement expense. For cylinders of 10 inches or less in bore the one-piece cylinder casting has no objectionable features. In fact, from the operator's viewpoint the one-piece cylinder is fully as serviceable as is the separate liner design. The cylinder walls are always amply thick for reboring.
American Diesel Engine.—This pioneer company employed a one-piece cylinder, as may be seen in Fig. 7. The bottom of the liner is not united with the jacket but is free to elongate without strain. This open end of the jacket cavity is closed with a cover ring. The top is not provided with cored water passages to the cylinder head, the water being passed into the head by outside gooseneck connections.
The lubrication of the cylinder is largely dependent on the splashing of oil from the enclosed crank-case. To make the oiling more certain, an oil line leads from a mechanical oil pump to the cylinder about midway down the cylinder.
American Cylinder Head.—This head, a cross-section of which appears in Figs. 7 and 62, is of irregular shape, one side carrying the cavity for the air admission valve. The exhaust valve cage is bolted to the lower side of this projection. The hot exhaust gases pass across the bridge or separator A, as does also the cold air charge. The alternate' heating and chilling of this bridge produce shrinkage cracks that speedily extend en tirely through the cast-iron wall. This allows the exhaust valve to leak. Many heads have been scrapped solely because of this bridge fracture. This is totally an uncalled-for extrava gance since in all instances the fracture can be repaired by welding.
The head is fitted with a relief valve. Unfortunately few operators test this valve; consequently it fails to function when an excessively high preignition pressure is experienced in the cylinder. The valve carbonizes and freezes to its seat unless relieved by being lifted at least once a week.
Standard Fuel Oil cylinder of the engine manu factured by the Standard Fuel Oil Engine Co. is of one-piece construction, when the power cylinder alone is considered. As outlined in Fig. 63, the liner and jacket are in one piece, the front end of which fits into the frame casting. The scavenging piston works in a bored cavity of the frame which is not provided with any means of cooling. The power cylinder, as mentioned above, is fitted into this cavity and is held by a flange. The cylin der casting is provided with ports, both for the exhaust gases and for the scavenging air. The air ports, at the top of the cylinder, are arranged to give to the air charge a whirling motion which materially assists in the scavenging of the exhaust gases; see Fig. 64. The water spaces in the bridges are small and tend to scale if the water is bad since this is the place of greatest temperature. If the spaces once fill with scale, the bridges are subject to fracture. Periodical cleaning of the water jacket is imperative.
Head.—The cylinder head, Fig. 65, is water-cooled and contains but one opening—that for file fuel valve. Since the; water line t the head is separate jacket cooling system, some engineers attempt to operrit& the engine on low loads with the head water line out. Since the head becomes hot, this does improve the combustion on low loads. However, there is danger in the liability of the head showing a fracture on cooling. The joint between the cylinder and the head should be metal to metal. In replacing the head the surfaces require a thorough cleaning to avoid the risk of small particles injuring the gas-tight joint.