So I can turn it without damage, but I won't be able to? Or do you mean I can turn it with a breaker bar without damage?Really just trying to assess the condition of the head, I plan to get a new valve, and anything else that may need replaced, I was worried the fact I couldn't turn it meant the whole thing was shot. Just waiting for some other manuals to come in the library as I find the procedure in Bentley to be a bit over complicated and want a second opinion.