7 1/4 drums fit on 8 3/4?

Your drums were probably replaced with replacement ones that would fit. after a drum is turned so many times, it becomes weak. Most have a number cast into them that indicates what is the maximum that can be taken off the drum before it should be discarded. Alternitively, one or both of the drums became warped and somebody replaced them. Thats the two most likely situations I can think of