My son has a 27" retina iMac and, last year, we decided to replace the HDD with an SSD. Mostly I wanted Josh to become more comfortable with maintaining hardware. I bought the new drive kit from OWC.
The repair requires a bit of patience and a good-size working space. Other than that, he had no trouble actually replacing the drive. I elected to handle replacing the adhesive, since he seemed pretty nervous about it and it seemed as though the price of failure would be high. I was meticulous about removing the old adhesive (a pretty tedious job), cleaning the parts with isopropanol, and being careful applying the new adhesive (which came with the OWC kit) to align everything correctly so as not to have to move anything later and potentially damaging the adhesive. Oh, and I made sure the machine would boot before I replaced the screen.
After the replacement, the new drive would usually boot and sometimes run for half an hour or so before crashing. We could never get his system fully restored onto it, and I believe that it soon started getting SMART errors. We shelved the project for the day, but that afternoon there was a crash from the room the computer was in. I returned to the room to find that the screen had fallen off the machine, traumatically disconnecting the cables.
Remarkably, the screen and cables were still functional. I took the drive out and put it in an external test jig and verified that it was defective. I got an RFC to return it to OWC, and they assured me that they would include a new adhesive kit. I put the old HDD in so Josh wouldn’t be without a machine and taped the display back on with blue painter tape on the exterior, leaving the failed adhesive on the interior.
The new drive arrived about a week later without the adhesive. Josh was anxious to have his computer back, so we tested and installed the new SSD and put the screen back with external blue painter tape again. It had kind of a steampunk look to it. For some reason, I had the notion that OWC was shipping the adhesive under separate cover, but it never came. I wrote and asked them about it, and they eventually shipped it.
I went through the whole remove-old-adhesive apply-new-adhesive dance again, but this time also taped the screen back with the blue painter tape. I left that on for a week to give the adhesive time to set, then replaced it with black electrical tape which would stretch and reveal if the internal adhesive was failing but (I hoped) prevent traumatic separation. This time, it held, and I eventually (with some trepidation) removed all the exterior tape.
In the end, we were successful in getting the HDD replaced with an SSD, but I’m afraid I failed at helping Josh become more comfortable with doing his own computer repair. OWC stood behind their product, but the fact that I essentially had to do the replacement four times meant that I would have been much happier just replacing the machine or having a shop do the replacement (though whether they would have detected the problem with the first SSD is hard to guess).
I guess the moral of this long-winded story is that it is doable, not too terribly difficult, but I would absolutely tape the display on for a week after re-installing it with new adhesive and don’t expect it to be a quick and simple task.