I am brand new to the forum and got here by searching for how to rebuild the great old Sears floor jack.
Two weeks ago my older brother gave me his Austin Healey 3000 Mk II that has been stored in his garage for over forty years along with the jack our father gave him to work on his classic cars that he was racing at the time. The jack would not hold pressure so I ordered a rebuild kit and found this thread. Really helpful.
One thing I read here, and apologize if it has been covered, is that a poster was asking if he needed to break a weld to remove the hydraulic cylinder and was told not to do that. On my jack, it is indeed tack welded in two places between the cylinder base and the frame and I was unable to lift the front of the cylinder to remove the spring and cotter pin as shown in the OP's great post. Only when I let the jack drop a few inches rather than risk getting a finger scissored off did I discover that fact when those little welds broke and freed the cylinder.
I still haven't removed the cylinder nut, though. I have a nice vise that is securely mounted to a flimsy cabinet style bench and ripped the top of the bench off with the torque I put on that nut. It took me over an hour to mount my Wilton to a substantial bench I use for reloading equipment and will tackle the nut this morning. I hate marring a nut with a pipe wrench but see no other way than that without spending a ton for a box end wrench that large.
One last thing about the vise is that mine is a swiveling model, and now I know why I read in a metalworking book recently to use only non-swiveling kind. When I torqued that nut with the cheater, the swivel feature broke loose even after being very tight, and the momentum generated ripped off the top of my bench. Another lesson learned the hard way. Later, Denny