These two hand operated machines were used (I don't know how successfully) years ago to resurface valves. Both operate by clamping the valve stem in a handle and turning the valve against a cutter. The first one is actually called "The Perfect Valve Lathe" and was patented in 1920. It actually has three adjustments so may be able to do a good job. The second one is cheaply made and I actually thought it was newer until I found it in a 1930 Western Auto Catalog, last picture. I have tried both of them and it would take a long time to actually resurface a burned valve.