Take care not to confuse the suction and exhaust valves as they are of the same shape but made of different materials.
FIG.: Marking on suction and exhaust valve stem
In the fig., S represents suction valve and E represents exhaust valve.
It is important to note that tappet clearance of suction valve is 0.40 mm and tappet clearance of exhaust valve is 0.50 mm which is measured by feeler gauge. The tappet clearance of exhaust valve is kept more as it is subjected to high temperature.