Does putting a 16gb logic board in an 8gb shell break it?

Alright so, my friend dropped his phone in water and broke it. He gave it to me to fix it up, so I tried drying it out with rice and using isopropyl alcohol and I got it to show the red battery charging screen. So I left it to charge and when I come back, all it gives me is a white screen. I didn't really understand why it was giving me a white screen after it had already shown the battery display just fine.

I happen to have an old iphone 3gs 16 gb that just looked like crap (broken screen, shell was scratched and cracked) but the logic board, to my knowledge, worked just fine. So I took out the 16gb logic board and put it in the water damaged iphone. I put everything together and shut the phone and turned it on. It would flicker and then shut off or show the recovery mode logo. I couldn't quite get it working, and then I thought that maybe the 8gb's shell wasn't the right size, so I put it back in the 16gb shell. Eventually I got it working and gave it back to my friend, but not 30 minutes later did it turn off and then show a recovery mode logo. Could it be because of putting it in a shell that was too small? Or is something else the problem? Any help in fixing it is greatly appreciated.