Figure 12-21.-Sectional view of a typicalvibration damper.Engine FlywheelThe flywheel mounts at the rear of the crankshaftnear the rear main bearing. This is usually the longestand heaviest main bearing in the engine, as it mustsupport the weight of the flywheel.The flywheel (fig. 12-22) stores up rotation energyduring the power impulses of the engine. It releasesthis energy between power impulses, thus assuringless fluctuation in engine speed and smoother engineoperation. The size of the flywheel will vary with thenumber of cylinders and the general construction ofthe engine. With the large number of cylinders and theconsequent overlapping of power impulses, there is lessneed for a flywheel; consequently, the flywheel can berelatively small. The flywheel rim carries a ring gear,either integral with or shrunk on the flywheel, thatmeshes with the starter driving gear for cranking theengine. The rear face of the flywheel is usuallymachined and ground and acts as one of the pressuresurfaces for the clutch, becoming a part of the clutchassembly.Figure 12-23.-Camshaft and bushings.Valves and Valve MechanismsMost engines have two valves for each cylinder, oneintake and one exhaust valve. Since each of thesevalves operates at different times, separate operatingmechanisms must be provided for each valve. Valvesare normally held closed by heavy springs and bycompression in the combustion chamber. The purposeof the valve-actuating mechanism is to overcome thespring pressure and open the valves at the proper time.The valve-actuating mechanism includes the enginecamshaft, camshaft followers (tappets), pushrods, androcker arms.CAMSHAFT.—The camshaft (fig. 12-23) is enclosed inthe engine block. It has eccentric lobes (cams) groundon it for each valve in the engine. As the12-19
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business