Disassembling a Lionel 1110 or similar Scout 2-4-2 or 4-2-2 locomotive isn’t too difficult. The biggest problem is knowing where the three screws are that you have to remove.
These particular locomotives weren’t really designed to be repaired, but there’s some basic work you can do on them with household tools. You can also replace dead motors with motors from certain other locomotives to get these trains running again if they have sentimental value to you. My 1110, which was my Dad’s first train, falls into that category for me, so I understand.