Valve clearance that is too tight is most likely to result in

Correct answer to question 54 (Auto & Shop Information): valves that never fully close and eventually burn

Method

Metal expands as it heats, so a clearance set too tight disappears entirely and holds the valve slightly open. The valve then loses its contact with the seat, which is how it sheds heat, and it burns. Too much clearance gives the tapping noise instead, which is noisy but far less damaging.