Tape Loop rhythms and beats

I just learned how to make cassette tape loops but I do not understand how you can possibly make a consistent beat with a seamless playback. because the piece of tape's length must remain constant how is this possible? ( im talking about something like the beginning of pink floyd's money. they use a tape loop of money falling and a cash register but how do they make it into a usable beat?)

ive been thinking maybe a multi track cassette recorder would help with this?