Fan and ShroudThe engine fan is usually mounted on the end of thewater pump shaft and is driven by the same belt thatdrives the pump. The fan pulls a large volume of airthrough the radiator core that cools the hot watercirculating through the radiator. In addition to removingthe heat from the water in the radiator, the flow of aircreated by the fan causes some direct cooling of theengine itself. On some construction equipment, such asdozers and track loaders, the fan blows air through theradiator vice pulling the air. Besides cooling the water,the blowing of air keeps sand, dirt, and debris out of theradiator. Some engines are equipped with a shroud thatimproves fan efficiency by assuring that all the airhandled by the fan passes through the radiator.Fan blades are spaced at intervals around the fan hubto aid in controlling vibration and noise. They are oftencurled at the tip to increase their ability to move air.Except for differences in location around the hub, mostblades have the same pitch and angularity.Bent fan blades are a common problem. They causenoise, vibration, and excess wear on the water pumpshaft. Visual inspection of the fan blades, pulleys, pumpshaft end play, and drive belts are part of your pre- andpost-operational checks. A bent or distorted fan or onewith a loose blade should be replaced. When the fan ismerely loose on its mounting, tightening is in order.Loose fan belts can be adjusted for proper tension,usually by adjusting the generator or alternator on itsmounting (fig. 1-47). A common method for measuringbelt tension is to press down on the belt at a pointmidway between the generator or alternator and the fanpulley, and measure the amount of deflection. Theamount of deflection varies and should be set to themanufacturer’s specification. A rule of thumb used inthe NCF for belt tension is no more than a one-half inchdeflection.Water JacketThe water passages in the cylinder block andcylinder head form the engine water jacket. Thepassages of the water jacket are designed to controlcirculation of coolant and provide proper coolingthroughout the engine. In the cylinder block, the waterjacket completely surrounds all cylinders along their fulllength. Water passages are also provided around thevalve seats and hot parts of the cylinder block. In thecylinder head, the water jacket covers the combustionchambers at the top of the cylinders and containsFigure 1-47.-Drive belt adjustment.passages around the valve seats when the valves arelocated in the head.ThermostatAutomatic control of the temperature of an engineis necessary for efficient engine performance andeconomical operation. Since all engine parts are in acontracted state when cold, the engine temperatureshould be brought to normal as quickly as possible. Thewater pump starts coolant circulating the moment theengine is started, which is undesirable during coldweather operations. Coolant circulation is restricted bythe installation of a thermostatically controlled valve, orthermostat, in the cylinder head water outlet. This valveallows coolant to circulate freely only within the blockuntil the desired temperature is reached. This shortensthe warm-up period. A bypass is used to direct the water1-35
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