Crank that nut down to at least 33 - 35 ft lbs, the flywheel won`t move after as long as the crank and wheel taper are clean and dry. Use a torque wrench if possible, its difficult for most to tighten a nut that tight as it feels like one is over tightening it with any other driver.
That's an M8 nut with spec torque of 24 ft-lbs. Have you ever had any problems using 33-35 ft-lbs? The M10 crankshaft nut has a 33 ft-lbs spec torque.