Burned up the engine.

All that white looking stuff is aluminum that has melted into the piston and valves

..and I do mean "burned up"the engine.  The threads in the spark plug hole were damaged and allowed the spark plug to loosen up.  The loose spark plug allowed the motor to run very lean and melted the piston.  This not only ruined the piston but also damaged the cylinder head, valves and exhaust cam beyond repair.