My project is replacing a head gasket on a 1998 Discovery after overheating. After it overheated I took it into my mechanic and he said it was a blown head gasket. Due to wanting to save money and learn more about my favorite car I decided to tackle the work myself. I have gotten down to the cylinders and am now cautious with what to do next. There seems to be a lot of build up on the pistons themselves though the bores look decent as far as I can tell. I don't see any obvious breaks in the head gaskets though there is some corrosion around the coolant chambers. My plan is to send the heads to get cleaned and machined flat if the head is warped (hopefully they aren't cracked). Should I have any other work done on them when the machine shop has them? But what about the gunk on the piston themselves? What recommendations are there for getting those clean?