I would second the low or very poor oil as the cause. Or some kind of obstruction of the oil supply hole.
slap a prothe head on it
It's garbage. Opps, I mean cheap chinese parts. It does work though. Just do a lot of searching for "prothe" before you do decide to purchase something major like that from him. He has a lot of unsatisfied customers. He does have a lot of satisfied ones as well though. There are ample used AAZ heads around. I'm sure if you put up a WTB thread you could get a good OEM one for a good price.