I recently purchased the Acela set.  I have noticed on the powered car that the pins/shafts which hold the gears in the power truck itself work themselves loose from their associated holes in the truck sideframes.  This causes the gear to fall in the truck and thus stoping the train from running.  I have noticed the flat metal contact which transfers power from the wheel to the circuit board rides up based on the rotation of the wheel and thus allows the pins to work free.  Is this an inherant problem or did I just get a bad one?  Also, are the pins supposed to be friction fit into the truck sideframes to prevent working loose.  Is there a remedy for my problem?  Thanks.