2 things can happened:
1) the main bearing is inserted in the wrong way, look from the backplate if you can clearly see the balls and not the ring from the cage holding the balls. At one edge of the inner ring of the bearing the rounding is bigger fitting the rouding at the same spot on the crankshaft.
2) one of the bearings not inserted far enough
Speed is only fiction but a 130+km/h MRS4 is for real.