Spine can become misshapen from misuse or from being stored badly. Over time, the glue hardens and the distortion become set which adds stress to the joints of the cover, causing them to fail.
The front cover of this Bible was detached so I removed the text block from the back cover and placed it between book boards in my lying press. When putting the it in the press I tried to reshape the spine bit only had a little improvement.
I peeled away as much of the spine linings as I could get to come off easily. I coated the spine with a thick mixture of methyl cellulose to soften the lining paper and old glue. After 10 minutes, I used my bone folder to scrap away more of the lining and then repeated the operation again. 
The old glue layer had softened enough so I could take the book out of the press and try to reshape the spine back to a more rounded shape. Then I applied another round of methyl cellulose and continued to remove the last of the lining and glue layers on the spine.
When the spine was finally clean I removed the book from the press and again reshaped the spine. I then returned it to the press to finish drying.
When handling large books like this, I tilt my laying press on its side in a stand I built for it. This allows me to place the book in on its side and rest it on the cheek of the press instead of trying to lower it from above and hold on to it while turning the screws. After the press is tightened I lift and turn the laying press over with the spine upright.
The press sit on the shelf at both ends. This allows the text block to hang below while I am working and I can store the stand and press separately.
To keep the shape of the rounded spine, I used three layers of paper and a layer of linen cloth on the spine. The paper of this Bible was very thin and had a good drape so even with a more heavily line spine it still opened well and the extra lining will help to hold the shape of the spine.
I then worked on the cover which was a heavy paper case embossed to look like leather. I reattached the front cover and reinforced the back hinge. 
