I haven't found the flywheel attaching nut to need a lot of torque unless there is a keyway burr on either the crankshaft or flywheel - which there usually is if it has sheared a key. Most people either don't deburr the flywheel bore at all, or do a sloppy job of it. You usually need to use blue and find out how much contact area you have. If you find a non-contact area close to the keyway on each side of it, you can be sure you have a keyway burr. And remember, always do a final bluing test with the key in place: a key that is too high, or can't get to the bottom of the keyway due to an internal burr, will deform the bore near the keyway, making repeated key failures inevitable.
