Originally Posted by PGT
some say that the face of the head is hardened and that you lose the hardness by excess skimming (this is the case with k series heads) but this can only be true if the material is exotic stuff like LM25 which is capable of hardenning but i dont know if YB heads are made of this. spoke to karl about this and he says skimming the head has no effect at all.
Cossie heads can go 'soft' if they've been subject to major overheating, you can get a hardness check done on the head to establish this.