Please help. I am trying to fix a 96 mustang. the engine is a 3.8 v6 . i put new main bearings because they showed sign of no oil. meaning burn marks. next heads went out for a valve job , new head gaskets just came in. now the problem cam was stuck. once i loosened the cam bolt in spun. cleaned everything . machine shop said cam is good. put in back on torqued down and wont spin again... any help would be greatley appreciated

 

im thinking maybe something with the cam spacer but not sure. thanks again