115hp flywheel loose

[bobev0204]

I have a 2002 115hp 4-stroke that has never been repaired. The engine was running fine for about 45 min then made terrible noise grinding and stopped. Had a certified Yamaha repair stator and broken crank key. Put in water and ran fine for 10 min then started making noise, little vibration. I stopped it and found the bolt on crank was getting loose. The tech swears he torqed bolt down to specs.. Any ideas what could make bolt get loose when tight??

[boats.net]

They need to check mating surface between flywheel and crankshaft to see was damaged when key sheered.