Can you post a pic to show where it is breaking? That might give all the experts in hear more to go on.
If it is just the mounting studs breaking, welcome to the club! There are many posts in here talking about replacing the crappy studs with quality steel.
is the motor mount parallel with the frame ?
if not, it will bend the stud when tightening and cause the stud to break from vibration
I have never broke a front stud but have broken rears when not tight enough
I didn't break the rear studs but i didn't use them i replaced them with high strenght bolts that were too long so i put one of the cheap kit nuts all the way to the head and used it like a thick washer