Principles of naval engineering - Historic Naval Ships Association

Chapter 22. -DIESEL AND GASOLINE ENGINESA- DIAGONALLY-CUT COMPRESSION RING B-LAP-JOINT COMPRESSION RINGC-OIL RING D- SLOTTED OIL RINGE-THREE PIECE OIL RINGFigure 22-17.— Types of piston rings.75.51The camshaft is driven by the crankshaftby various means, the most common being bygears or by a chain and sprocket. The camshaftfor a 4-stroke cycle engine must turn at onehalfof the crankshaft speed; while in the 2-strokecycle engine, it turns at the same speed as thecrankshaft.The location of the crankshaft in variousengines differs. Camshaft location depends onthe arrangement of the valve mechanism. Thelocation of a camshaft is shown in figure 22-14.One of the principal engine parts which hasonly rotating motion is the crankshaft . As one ofthe largest and most important moving parts inan engine, the crankshaft changes the movementof the piston and the connecting rod into the rotatingmotion required to drive such items asreduction gears, propeller shafts, generators,pumps, etc. As a result of its function, thecrankshaft is subjected to all the forces developedin an engine.While crankshafts of a few larger enginesare of the built-up type (forged in separatesections and flanged together), the crankshaftsof most modern engines are of the one-piecetype construction. A shaft of this type is shownin figure 22-19. The parts of a crankshaft maybe identified by various terms; however, thoseshown in figure 22-19 are common in the technicalmanuals for most of the engines used bythe Navy.The speed of rotation of the crankshaft increaseseach time the shaft receives a powerimpulse from one of the pistons; and it thengradually decreases untilanother power impulseis received. These fluctuations in speed (theirnumber depending upon the number of cylindersfiring in one crankshaft revolution) would resultin an undesirable situation with respect to thedriven mechanism as well as the engine;therefore,some means must be provided to stabilizeshaft rotation. In some engines this is accomplishedby installing a flywheel on the crankshaft;in others, the motion of such engine parts asthe crankpins, webs, lower ends of connectingrods, and such driven units as the clutch,generator, etc., serve the purpose. The needfor a flywheel decreases as the number ofcylinders firing in one revolution of the crankshaftand the mass of the moving parts attachedto the crankshaft increases.A flywheel stores up energy during the powerevent and releases it duringthe remaining eventsof the operating cycle. In other words, when the563