In the next few posts I will talk about recasing a text block into the cover of a book.

The hinge is the weakest part of a case bound book. As explained in an earlier post on how books are put together, the text block is constructed in one operation while the case is constructed in another operation.

spines

The spine of the text block is covered with crash, and the crash is attached to the book board. The crash is covered by the pasted down endpaper.
Over time, gravity pulls the text block away from the cover, or the crash can
be damaged which allows the text block to separate from the cover. If the
cover is in good condition, the text block can be recased into the original
cover.

Some text blocks are so large and heavy that they will always be prone to
falling out of their cases. In such a circumstance, it is wise to recase the
text block so it is flush with the bottom of the case. That way the shelf can
support the entire text block.

The book case joints must be in excellent condition to reuse the case as is.
If the joint area is worn, repair the cover using the techniques outlined in
earlier posts as a guideline. The repair will differ slightly from the instructions if the text block is not be attached to the cover boards but the basic principles are the same.
When the rebacking (spine and hinge repair) is complete, recase the text
block.
Check the endpapers carefully and determine whether they can be reused or
if they need to be replaced or repaired.