piston rings

Could anybody tell me the max bore size for standard pistons please? Looking around and I keep coming up with 79.5 bore size and 79.5 pistons, but I assume there must be a clearance built into this. I finally got around to pulling the head on mine to investigate the ridiculous oil consumption...

Basically i'm in the engine as i'm replacing the head on an AAB 2.4d with 210k on the clock. Ive been advised by some whilst i'm here do the piston rings, over size ones. Others have said if it aint broke, "why fix it" and "it could be a can of worms" - mechanics love puns eh! Since I bought...