Chapter 22. -DIESEL AND GASOLINE ENGINES 



A- DIAGONALLY-CUT COMPRESSION RING 



B-LAP-JOINT COMPRESSION RING 



C-OIL RING 



D- SLOTTED OIL RING 



E-THREE PIECE OIL RING 



Figure 22-17.— Types of piston rings. 



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The camshaft is driven by the crankshaft 

 by various means, the most common being by 

 gears or by a chain and sprocket. The camshaft 

 for a 4-stroke cycle engine must turn at one- 

 half of the crankshaft speed; while in the 2-stroke 

 cycle engine, it turns at the same speed as the 

 crankshaft. 



The location of the crankshaft in various 

 engines differs. Camshaft location depends on 

 the arrangement of the valve mechanism. The 

 location of a camshaft is shown in figure 22-14. 



One of the principal engine parts which has 

 only rotating motion is the crankshaft . As one of 

 the largest and most important moving parts in 

 an engine, the crankshaft changes the movement 

 of the piston and the connecting rod into the ro- 

 tating motion required to drive such items as 

 reduction gears, propeller shafts, generators, 

 pumps, etc. As a result of its function, the 

 crankshaft is subjected to all the forces de- 

 veloped in an engine. 



While crankshafts of a few larger engines 

 are of the built-up type (forged in separate 

 sections and flanged together), the crankshafts 

 of most modern engines are of the one-piece 

 type construction. A shaft of this type is shown 

 in figure 22-19. The parts of a crankshaft may 



be identified by various terms; however, those 

 shown in figure 22-19 are common in the tech- 

 nical manuals for most of the engines used by 

 the Navy. 



The speed of rotation of the crankshaft in- 

 creases each time the shaft receives a power 

 impulse from one of the pistons; and it then 

 gradually decreases untilanother power impulse 

 is received. These fluctuations in speed (their 

 number depending upon the number of cylinders 

 firing in one crankshaft revolution) would result 

 in an undesirable situation with respect to the 

 driven mechanism as well as the engine;there- 

 fore, some means must be provided to stabilize 

 shaft rotation. In some engines this is accom- 

 plished by installing a flywheel on the crankshaft; 

 in others, the motion of such engine parts as 

 the crankpins, webs, lower ends of connecting 

 rods, and such driven units as the clutch, 

 generator, etc., serve the purpose. The need 

 for a flywheel decreases as the number of 

 cylinders firing in one revolution of the crank- 

 shaft and the mass of the moving parts attached 

 to the crankshaft increases. 



A flywheel stores up energy during the power 

 event and releases it duringthe remaining events 

 of the operating cycle. In other words, when the 



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