Cylinder Head Valve Inspection
After removing the valve from the cylinder head and cleaning, it should be inspected for:
No margin: The margin of the valve will get pounded. If the margin is to thin the valve will heat up and burn prematurely.
Pitting, Burning, and Cracks : This usually happens to exhaust valves, because they run hotter than the intake valves do. Exhaust valves are typically made out of high quality stainless steel. But they don't benefit from the cool air and fuel the intake valve receives on the intake stroke. Valves will burn when they’re left open during combustion and exposed to extreme temperatures. As the spring weakens, the valve sticks open a little longer.
Cupped Heads: Once the head is cupped or mushroomed, the valve must be replaced.
Stretching: Stretching is the narrowing of the neck above the head. This affects the length of the valve.
Worn Keeper Grooves or Valve Stem Tip: Inspect keeper grooves, rotators, and retainers for wear and replace if necessary. If a keeper or retainer pops out of place, the valve will drop in the cylinder causing engine damage. Also, a worn valve stem tip can cause retainer and rocker arm damage.
Valve Stem: The valve stem should be measured with an outside micrometer in several places to check for uneven or excessive wear.