Answer for Why is valve clearance important

The valve stem expands on getting heat. Because of this valves are not .properly closed. Besides this there is risk of their stem or operating push rod getting bent. Therefore, it is necessary to keep clearance between tappet and stem or between valve stem and rocker. This clearance is kept generally 0.006″ to 0.016″ for inlet valve and from 0.009″ to 0.020″ for exhaust valve.’