We operated a lot of heavy equipment and eventually bought a Sioux valve machine and seat grinder as well as a Hall Toledo orbital seat grinder for grinding stellite seats, all because we were getting screwed anytime we sent a head out for a valve job. For example, we had a lot of 71 series Detroits. Send out a 4 valve 6-71 head, and the first thing they'd do is throw away 24 sodium filled valves at $25 a pop. Then take a facing cut across the head, which meant all the injector tubes now need to be replaced. Parts and labor would run a thousand bucks (20 year ago pricing) on a head that had no apparent problems. We did the remainder of the work in house, and the cost for the head work would be 2/3 as much as a Mahle/Clevite overhaul kit that included pistons, rings, liners, bearings, and gaskets. In the dozen or more Detroit heads I did after we bought the valve equipment, I never found a head that needed to be faced. Found maybe 10 valves that needed replacing. 10 total, not 10 per head. Funny thing was, I found more seats that needed replacing than valves, yet in all the heads we'd sent out over the years, no shop ever found a bad seat. I guess there's less profit in replacing a seat as compared to tossing a valve and grabbing a new one off the shelf. Same deal with guides. Outside shops never seemed to find a worn one, yet when I checked them on the heads I did, I regularly found enough near or past the wear limit to justify replacing all of them. 3 different shops, and all the same. Might as well have a monkey trained to throw away and replace all the most expensive pieces, ignore the rest, and git 'er on out the door.