This is when the engine valves are reconditioned. It requires removing the cylinder head, disassembling the head and checking it for cracks or warpage (a common problem on aluminum cylinder heads), regrinding the valve faces and seats, replacing or restoring the valve guides, installing new valve guide seals, inspecting the springs, and other valve hardware, then reassembling the heads and putting them back on the engine.
![](https://scottsautomotiveinc.com/wp-content/uploads/2012/04/valve-jobs.jpg)