After I had pulled the fan assembly from my truck yesterday I noticed that the fan pulley had worn a partial half moon shaped groove into the timing cover. One end of the groove was deeper than the other - I would estimate that the deepest part was at least 1/24 to 1/16 of an inch. Does any one have any thoughts as to what could cause this. Obviously there is something wrong with the fan pulley or the fan support hub/bracket. I suppose the timing cover could be part of the problem as well. The truck only has 68,000 miles on it. Once I get the cover off, I can tell how much metal was left before the groove wore completely through the cover.

 

Either the bearing is gone or the bracket wasn't tightened down properly IMO