To further little Nola's (Devil made me) education; Valve & seat grinding were necessary in the time when seats were directly ground into the block casting into the early 50s. Cast iron valve seats have a limited service life, particularly on the exhaust side, so the valve got pulled, a mandrel went in the stem hole and a stone with a hollow arbor sized to ride the mandrel ground the seat back to a good workable surface. The stone was driven by a electric hand tool similar in appearance to a Milwaukee right angle drill. Sioux and Black and Decker both made good quality drivers as did some others.
The valve itself if not excessively eroded was placed into the chuck of a bench mounted valve grinder and rotated against a spinning grinding wheel in a manner similar to tool post grinding in a lathe. The facing angle of the valve was set on the bed of the grinder.
Preferred sequence was to grind all valves first, check to see if they were still usable against the seats, then grind the seats to match the valves.
The wheel for grinding the seats was angled with an angle settable dresser to match the valves.
After valve and seat were ground, it was generally necessary to remove material from the base of the stem to compensate for the valve sitting lower in the casting and get the proper valve setting.
The invention of Stelite insertable valve seats for blocks pretty much rendered the reseating half of the job obsolete, and sodium filled valves that dissipated heat better gave valves much longer life. Auto Shop classes around here pretty much stopped teaching the job 20 years ago and sold the machines. I bought 2 complete Sioux machines when they did and made a couple bucks selling them.
I should probably also point out when the valves were removed they were inserted into either a drilled board or piece of cardboard to maintain their location in the engine. They were removed and worked 1 at a time, and a helpful kid who put them all in a Crisco can to save space could and did get his ass whipped for doing so. I learned FAST!
