Harmonic Balancer Split in half

[CrissCross]

Hello every one I have a 97' Mazda Mpv and just the other day when I went to start it the harmonic balancer split in half. I ordered the replacement from the dealer but I was more worried about what could cause this. Just a few months ago I replaced the belts and when I did I over tightend the bult tensioner going to the power sterring and busted the tensioner I riged it buy turing the tensioner upside down and putting a nut on the other end I just never got arround to ordering the replacement tensioner.

Does would this have caused the harmonic balancer to break. The dealer said that if the belts were over tightend then over time this could happen becuase the harmonic balancer is fused with two pieces of metal by a piece of rubber. Let me know what you think.

thnaks for your time.