The fywheel is held by the taper not the key, the key is there to align ignition timing, if the key keeps shearing there is an issue with the flywheel or the crank taper. Also check crank is not bent as high vibration could also shear the key. Bear in mind that the key is also supposed to shear if you hit somthing with the blade.
Husqvarna man, April 2010
