I blew my rear rotor on a 13bt with s5 rear iron years ago. I'm debating an engine build now and so I looked at my irons today. I see lots of marks and a scratch on the sides. I can use my nail and feel it catching. Is there a thickness spec I can measure to know if my irons have been lapped before, and/or if the scratch is beyond lapping?

I also have old irons that came off an old s4 t2 that blew a rotor, but the sides aren't scratched. This engine has some rust on it, its not ported, and the rear iron is the s4 t2, not s5.