Both the guides and valve stems can show signs of wear.  While the valves are simply replaced, new guides or guide liners can be installed in the heads.  New guides can be iron or bronze while guide liners are typically bronze.  Guide liners can be either the screw in (threaded) or press fit in style.  I'm partial to the screw in variety.

Lorena, Texas (South of Waco)

Just pulled the valves out of one of my spare set of  ECZ-G heads. By feel, noted some side play in  3 valves at the valve end. Guessing, because I don't really have a tool to measure accurately with, that one end valve guide may be 10 thou or more worn at the valve end. The factory manual says the guide wear limit on exhausts is 0.0065"   And do the valve stems sometimes show appreciable wear?   Are the heads likely candidates for some type of guide liner ? If so what make?  All info appreciated
 


Paul