Check the pulley for any damaged (or "wollered out") holes. If all is ok there, reinstall it, utilizing RED LOCTITE on the bolts. Recommend the OEM bolts be used... and regardless of any "thread paste" on the bolts- USE RED LIQUID LOCTITE ALSO.

Torque spec is printed on the top of the pulley, in most cases.

Inspect belt carefully for any signs of wear- replace if AT ALL IN QUESTION (you don't want any additional vibration here).

Once the pulley is installed, check for any "up and down, or side to side" play in the crankshaft (endcap) bearings of the compressor. This is usually easiest to note with the compressor at the "bottom of it's stroke".

Bolts do sheer occassionally.....