Just completed a second Spinning hard drive (Seagate 500GB 7200rpm) to Solid State Drive transplant in an older Imac. This time it was a 21.5″ mid2011 Imac, and it was different from the 21.5″ late2015 model I did first.
All in all it took about 35 minutes and the next one will go faster.
The machine was powered down, unplugged and left to cool for a time. The screen cover was attached by magnets this time, not double sided adhesive… so it came off quite quickly. The screen itself had nine Torx10 screws holding it in. I had only a Torx9 bit but it worked well. The supermagnets that held the screen cover on did attract both bit and screw a lot.
The display came out of the case enough to start disconnecting four ribbon cables, only one of which had a latch mechanism. The Drive itself came out with only two torx8 screws, the sata power and data cables removed.
The 240GB SSD went in, connected to the cables and just left in the cavity unsecured and with no special temperature sensor for fan control that many articlse write about.
The four ribbon cables went back in without issue, the display reinserted and screwed in and the screen cover clipped on without issue.
Power up ran normally if maybe just a little faster.
Previously the 240GB SSD drive was in an external USB3 case (upto 5Gbps), now it is connected internally to a SATA3 connection (upto 6Gbps)… so if anything, it might be just a little bit faster.
powerup sound to logo 20seconds
powerup sound to login 30 seconds.
Not bad at all.

This should give the Imac a longer life, especially since it will now run cooler without the spinning drive inside, and use less power.
Now we can start looking at another half dozen machines in the near future.
* updated 2019 May 02 * completed two more mid-2011 21.5″ Imacs with the magnets without any issues, both in under 30 minutes each.