Most engines have cooling-water passages within the cylinder head. In the cylinder head, these passages generally surround the valves. In diesels, the water passages also surround the in-jectors. Usually, the passages are cast or drilled as an integral part of the head. In some cylinder heads, such as those of various General Motors engines (fig. 7-15), each injector is inserted into a thin-walled copper tube that passes through the water space in the cylinder head. This design

Figure 7-15 .-Liquid cooling around valves and injector in the cylinder head of a General Motors engine,

serves to ensure sufficient cooling. The lower end of the copper tube is pressed into the cylinder head and is flared over; the upper end is flanged and sealed with a neoprene seal. The flared lower end and sealed upper end prevent any leaks around the copper tube. The exhaust passages, exhaust valve inserts, and injector tubes are completely surrounded by cooling water. Cooling of these areas of the cylinder head is further assured by the use of nozzles installed in the water inlet ports of the head. (Refer to fig. 7-15.) Nozzle holes are so positioned in the cylinder head that the comparatively cool water that enters the head is directed at high velocity against the sections of the head that are subjected to the greatest heat. The passages in the cylinder head receive water from a jacket or from passages, either of which may be an integral part of the cylinder liners or the cylinder block. Water flow to the cylinder head is almost always upward from the liner or block.