Edit: Dave...you posted just before I did...this isn't in response to your post...I'm in full agreement w/ you FBD.




That may be so, if one is using some sort of power tool to spin the valve and applys too much pressure...uses too coarse a compound...and/or if one is mechanically inept/ham handed.

IMO if you're just talking about cleaning the valve face and seat, you can do it by twirling the stem between your thumb and forefinger with the "Soft Scrub" or Copper bottom pan cleaner like I mentioned previously. The whole process only takes about a minute per valve.

If you are removing any significant amount of metal, then you are doing it wrong.