my fisrt factory aluminum pulley broke.sent it spinning into fan on interstate 84 into the fan blades,destrioded everything in front of it and dumped coolant in about 20 seconds about 4000 rpm.it cracked all around the bolts,but they where tight.got back from LVD dragway and heard what sounded like broken distributer or timing chain loose,was again a broken factory pulley broken all around the bolts again and pulled off with my fingers-but alt drive part towards crank tight and no problems.this saw steel and lucky was a busy day as next run could have wiped fello racer.cast crank,ly rods trw dome pist0ns.no vibs feel at all b&m flex-neutral converter.no way both times balancer bolts not tight.if it wasent for rattle,never notice.