Cast iron with Crome 25%
There is 4 exhaust and 8 inlet valves
inlet and exaust valves are usually opened by a lobe on a crankshaft, either directly, or with a pushrod and rocker arm assembly.
Most intake valves are made of the same material as the exhaust. They are heat resistant treated high carbon steel, as are the valve seats. The exhaust valve is usually larger in diameter to aid in scavenging of the spent hot exhaust gas. Some more expensive engines have sodium (Na) filled exhaust valves to aid heat transfer to the valve seat to help cool the valve.
Lobes on camshaft spaced correctly
same direction and forward.
An inlet and exhaust valves are two separate things. The inlet valve lets the fuel/ air ,ix into the cylinder. The exhaust valve opens to let the pressure out after the mix has burned, releasing the gasses. Then the process starts over again.
cast iron
this is a mechanics job you have to remove inlet manifold,exhaust manifolds,and then remove heads to replace the valves
A machine shop that rebuilds engines has equipment to regrind the valves and valve seats.
Inlet valves 0.010 inches (0.25mm) Exhaust valves 0.008 inches (0.20mm)
0.4 mm for exhaust valves and 0.35 for inlet
Three. Inlet valve, fuel injection valve, exhaust valve.