Chapter 22. -DIESEL AND GASOLINE ENGINES 



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GM 278A 



GM 268A 



GM 6-71 NAVY 



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Figure 22-15.— Cylinder liners of diesel engines. 



for engines of the opposed-piston type, the 

 space at the combustion end of a cylinder is 

 formed and sealed by a cylinder head which 

 is a separate unit from the block. (See fig. 

 22-14.) 



A number of engine parts which are es- 

 sential to engine operation may be found in or 

 attached to the cylinder head. The cylinder head 

 may house intake and exhaust valves, valve guides 

 and valve seats, or only exhaust valves and re- 

 lated parts. Rocker arm assemblies are frequen- 

 tly attached to the cylinder head. The fuel in- 

 jection valve is almost universally in the cylinder 

 head or heads of a diesel engine, while the 

 spark plugs are always in the cylinder head of 

 gasoline engines. Cylinder heads of a diesel 

 engine may also be fitted with air starting valves, 

 indicator and blow down valves, and safety 

 valves. 



The number of cylinder heads found on 

 engines varies considerably. Small engines of 

 the in-line cylinder arrangement utilize one 

 head for all cylinders. A single head serves 

 for all cylinders in each bank of some V-type 

 engines. Large diesel engines generally have 

 one cylinder head for each cylinder. Some 

 engines use one head for each pair of cylinders. 



In most cases, the seal between the cylinder 

 head and the block depends principally upon the 



studs and gaskets. The studs, or stud bolts, 

 secure the cylinder head to the cylinder block. 

 A gasket between the head and the block is 

 compressed to form a seal when the head is 

 properly tightened down. In some cases, gaskets 

 are not used between the cylinder head and 

 block; the mating surfaces of the head and block 

 are accurately machined to form a seal between 

 the two parts. 



PRINCIPAL MOVING PARTS.-In order that 

 the power developed by combustion can be con- 

 verted to mechanical energy, it is necessary for 

 reciprocating motion to be changed to rotating 

 motion. The moving parts included in the con- 

 version process, from combustion to energy 

 output, may be divided into the following three 

 major groups: (1) the parts which have only 

 reciprocating motion (pistons), (2) the parts 

 which have both reciprocating and rotating 

 motion (connecting rods), and (3) the parts 

 which have only rotating motion (crankshafts 

 and camshafts). 



The first two major groups of moving parts 

 may be further grouped under the single heading 

 of piston and rod assemblies. Such an assembly 

 may include a piston, piston rings, piston pin, 

 connecting rod, and related bearings. 



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