After rewiring my motor for 120V, I connected the ends to a power cable cord so I can plug it in an outlet without really knowing which is L1 and L2. When I plug it in the outlet, the motor did start running. However, after like 30 seconds there was a bang and spark where the wiring connected and I think I saw something inside the motor spark too. Does this mean that my motor is dead now?

I would say so.