Originally Posted by userix
I weigh 160lb
That's not enough to cause any problems. I weigh 215.
In that case, as long as the motor mounts were all tighten properly, then the frame is probably at fault imo. That's assumeing you weren't jumping it, or running WFO for long periods of time.
Considering how cheap low end bicycles have gotten, I would buy a new bike, and use your old one for a parts bike rather than fool around trying to save the one you've got.
I recommend a OP Roller from wall mart as a good replacement for your bicycle. It's cheap, looks about the same as your bike, and is Aluminum.