So, I was wrong

Apparently, my memory was incorrect and there is no manual override (hand crank or otherwise) for the space shuttle orbiter payload bay doors. Although the door latches can be manually engaged from inside the payload bay, should it jam when the doors close. And, the power drive unit for the doors can be manually disengaged, which tells me that if there was ever a real need to, there probably is a way to get the doors either open or closed without using the motors. But it certainly wouldn't be a lot of fun.