8 ft/lbs (96 in/lbs) is the max for an M6 bolt or screw, but you don't want to use that, not with steel or stainless steel bolts going into 30+ year old alloy cases. You see what happens when you try that. Stripping the threads out of the hole will also be a common occurrence. I use 80 in/lbs. It's more than tight enough, but not so tight that you're stripping things or breaking bolts off.