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

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

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Automobile Engineering in ME
The function of a proportioning control valve (PCV) in a brake system is to

Cause less brake fluid pressure to act on the rear brakes than on the front brakes when the fluid pressure exceeds a predetermined level
Cause less brake fluid pressure to act on the front brakes than on the rear brakes when the fluid pressure exceeds a predetermined level
Ensure that equal pressure is supplied to the front and rear brakes throughout every braking operation
Reduce the brake fluid pressure when the brakes approach their lockup point

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