Re: thumper cams
With sand cast parts, which it looks like cast-iron cams still are, sand can imbed itself in the outside of the metal. When those parts are ground, the sand will be knocked out, leaving a hole. It's what happens constantly when maximum productivity/profit are the goal. The cores will be made with less metal to grind off, leaving a surface that may have more flaws. It's what any of us would do if we were in business. The problem is not catching it before it goes out the door.
What I also see on that cam is an indication that the grinding coolant is not well maintained, which leaves 'dirt' in the ground finish. Grinding coolants are cleaned by magnetic and settling tank methods, and sometimes with filtering methods: another labor intensive process that appears to make no profit. In my opinion, one of the things that set Isky apart from early cam grinders was the finish on their roller cams: almost mirror-like. No dirt there. You could tell by the finish you had a first class product.
406 SB, Original Bill Thomas '63 Rochester FI
AFR 210, Lunati 501C2LUN, 255/263@.050", .628"
10:1, TH400, 3.31's, 4400 SS
"Life is too short to not run a solid roller cam."
"Nothing is impossible; if you don't know what you're talking about."