The main purpose of engine valves is opening and closing intake and exhaust holes. When intake valve is opening the fuel air mixture enters to the cylinders. And when exhaust valve is opening burned gases are expelled. Valve is an element of Valve mechanism.
The valves have some types by their shape: mushroom or tulip. You can see various shapes and types of these valves shown at the Figure illustrates.
Types of valves
The main parts of valves are head and stem. The valve should kept cylinder in isolation during comression stroke and power stroke.
A smooth transition from valve head to stem reduces resistance for gas moving by opening valve. The valves in the cylinders of Vehicle engine are subjected to high temperatures, so the metal alloy in the valves must be able to resist all factors as corrosion, and operating stresses.
Engine valve has a margin on the head, to make it tight to valve seat. Valve face is grinding by valve grinder to valve seat. A dedicated valve grinder is used to grind the valves due to the very fine.
The engine valve is held in a highly accurate chuck. The angle is setting – usually 45 degrees. Speed of rotation of the valve is depended by valve diameter for the smoothest possible finish. The amount of metal to be removed at each pass is set on the slide and then the grinding wheel is passed along the face of the valve with lever.
After grinding this valve is now well fit to the seat, so now ground and is complete. Finally matching of the seat and valve is achieved through lapping.
Engine valve material
Intake valve operates at lower temperatures than exhaust valve, so it made of chromic-nickel steel. In order to made exhaust valves are used much more heat resistant materials as nichrome, silchrome, or cobalt-chromium steel.
Heads of inlet and exhaust valves can be same or different diameters. Ussually, the head of inlet valve does more diameter than head of exhaust valve to provide improving cylinder filling. For intake and exhaust valve sizes calculation you should know engine’s bore, stroke, and rev limit. So you can calculate the ideal sizes for the intake and exhaust valves. For example, engine with a 1,588 cc (bore of 79.5 mm and stroke of 80 mm) and a rev limit of 6,000 RPM should have a 36.4 mm intake valve and a 31 mm exhaust valve. This calculation uses the following formula:
Valve diameter formula
Valve diameter = √((rpm × stroke × bore²) ÷ 2,286,000)
For example, the Melling Intake Valve of Ford -150 has Head Diameter (in): 1.752 and Head Diameter of the Exhaust Valve (in): 1.452.