Well the first time it broke there was nothing that I could have done! (previous owner never replaced timing belt tensioner, pulley broke...bent all the valves :( )
The second time it broke, it was the machine shops fault for not tightening down one of the intake cam sprockets, thus leading to timing belt slippage. I had to tear it apart to check the valves etc.
Recently, the motor broke for an uknown reason. I think my underdrive pulley caused a rod nut to vibrate off, but I am not sure. I guess that one could be considered my fault because I bought a pulley knowing the risks.