this is what happens when you use the wrong fan belt pulley on a 356 - 912 engine... my error i bought a aftermarket belt that ....it was junk... I only use the Continental belts  now.. the belt that exploded n took out the inner pulley half was just too small n thus too tight... the inner got hot n exploded... one always needs to retighten the nut that secures the pulley as well. 10 spacers give the correct width.