Figure 1-50.-Expansion tank.Figure 1-51.—Air-cooled engine.surfaces and the cooling air. Some heat must be retainedIn air-cooled engines, the cylinders are mountedfor efficient operation. This is accomplished by the useof thermostatic controls and mechanical linkage thatopen and close shutters to control the volume of coolingair. You will find that air-cooled engines generallyoperate at a higher temperature than liquid-cooledengines, whose operating temperature is largely limitedby the boiling point of the coolant used. Consequently,greater clearances must be provided between themoving parts of air-cooled engines to allow for theincreased expansion.independently to the crankcase so that an adequatevolume of air can circulate directly around eachcylinder. The circulating air absorbs excessive amountsof heat from the cylinders and maintains enoughcylinder head temperatures for satisfactory operation.The cooling action is based on the simple principle thatthe surrounding air is cooler than the engine heat. Theprimary components of an air-cooled system are the fanand shroud and the baffles and fins. A typical air-cooledengine is shown in figure 1-51.1-37
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