Automobile Engineering in ME
A worm gear is used as the pinion for the rack and pinion type of steering gearbox, because it

Reduces the amount of kickback for large steering angles
Allows the steering wheel to be turned by a greater amount when steering
Makes the steering more responsive
Improves steering comfort when steering wheel is turned to effect small changes in the direction of forward motion

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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
Reduce the resistance to sliding that occurs between the cam and the tappet
Make the crankshaft turn smoothly
Increase the speed at which the valves move up and down

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