When I replaced my crankshaft pulley (from the late model V6 with defictive rubber), I put some blue locktite on the bolt to help prevent it from coming loose.
If the 27mm bolt came off easy, then it wasn't put on tight enough to begin with.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles