zyudimosha: Mods and patches do not help to solve the problem. I've tried almost everything. However, I accidentally found a solution that helped in my case. If you add in the Fallout 4.ini file in the [General] section bUseCombinedObjects=0, then the Mechanic's lair can be passed, after that you can delete the line and forget about this quest.
Odijm: Tried this today, still crashes. I wasn't sure which .ini because I don't have anything just called fallout4.ini, I have defaults and preferences. Put it in both files and it still crashes.
Update: Took a gamble and turned off collision detection. and walked right through the tunnel with no crashes.
I had this issue as well in my last game, and I made it past the lockers by just not looking at them. But then I died and had to start over (I'm playing survival, perma-death) so when I get there again I plan on trying this fix. But I'm posting just to tell you that the Fallout4.ini file should be, if you just did a default installation, in your Documents/My Games/Fallout4 folder. Also in that folder is a folder called Saves, which is where your save games are (default settings).
In the main directory it has just those ini's you mentioned, which are defaults. The specific ini file the game uses is located in Documents/My Games/Fallout 4/