Automobile Engineering in ME
It is necessary to maintain the valve clearances as they

Allow for lengthening of the valves owing to the heat of combustion
Make the crankshaft turn smoothly
Increase the speed at which the valves move up and down
Reduce the resistance to sliding that occurs between the cam and the tappet

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Automobile Engineering in ME
In a ventilated disc brake

A duct directs air towards the caliper for cooling while the vehicle is moving
Caliper is covered with cooling fins
Disc contains many small holes for optimum cooling performance
Disc contains radial vanes between its rubbing surfaces for optimum cooling performance

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