What causes a endbell to fall out?
 

Hi, I heard many medusa motor's endbell fall out during runs & magnet crack up?

Two reason I know is temp too high & the car jump too much.

Magnet failure is rare. The endbells are only pressed into place, so after a while they simply work loose- just like feigaos and old neu motors. Easy fix is just to glue them in place with some red loctite, or even do like BrianG did and use 2 or 3 tiny little screws to hold them in place, like how the vxl and newer neus do. Mike's motor clamp is another great solution, if he ever gets around to making them again.. *hint hint* :mdr:

In my case, I was going in reverse and the truck hit a curb. When that happens, the backwards momentum of the rotor popped off the endbell. I'm sure it can work its way loose over time like Neil said.

What cause the magnet to crack then?

Rpms that are too high, defective magnet (weak spot), the adhesive lets go and it hits the coils/core, etc.

too much rpm, or debris in the motor. Or you got a bad magnet.

You meant too fast then too hot? Then the glue melt? Can the rotor break the magnet when the endbell pops out?

Yep, if one end of the shaft is not suporrted the magnet can contact the windings and shatter. Sometimes the magnet comes loose from the shaft, either heat or rpms can cause this.