A few of the head bolts (three, I think) are located in recessed "wells". If your engine is sludged up, you may not be able to see them and wonder why you can't get the head off. Also, on some engines, one of the head bolts is hollow for top end oiling. Check them as you remove them and make sure it goes back in the same place during reassembly if you have one. There are 18 head bolts total.
