The used heads purchased from Clark's Corvair needed rebuilding I got them rebuilt at Zelmore automotive machine shop ( new valves and guides) which I supplied from Clark's. The cylinder head gasket surface was rough on both heads to clean the surface up. I built a tool out of a 1/2 inch piece of flat steel cut to just under 3 13/16 round diameter (cylinder head bore size) and a 3/8 NC thread tapped in the centre at a machine shop. I purchase 5 inch round sand paper 220 grit to 400 grit which Istuck on the back of the disc plate and trimmed the excess off using a ball peen hammer. With a 3/8 drive rachet and 9/16 socket using my right hand I rotated the disc and with my left hand I applied pressure. I used 10 - 5 inch discs 220 grit and 5 - 5 inch 400 grit dics to complete both heads. I measured with a caliper on all head holes to make sure depth was all equal. I only removed a small amount of material on each hole to clean up, only the outside part of sandpaper on disc came in contact with head surface. This process is usually done by a fly cutting tool at specialized machine shops for corvair heads. I must say the results where very successful and the cost was minimal to build the tool.
