What is it about those pre-ai lenses that can cause damage? That'd be good information for me to have.
It's from the way the original F-mount lenses were manufactured, and how Ai'd lenses were changed to 'key' the camera as to the lens' maximum aperture.
Originally, Nikon made their F-mount lenses with a solid ring around the mount. Note how the black portion of the barrel in the lower right extends past the silver part of the lens mount... it's a solid ring all the way around the lens.
When they created the Ai system (Automatic Indexing), they needed a way for the lens to 'tell' the camera what the maximum aperture is on the lens. This was done by removing most of that ring, and leaving the end in a position that was related to the lens' maximum aperture.
They added a ring around the camera's lens mount to 'receive' this raised portion of the lens. Take a look at your camera, with the lens removed, and you'll see it at about the 1:30 position. You can take your finger and gently move it.
The Ai lens 'keys' this ring, and how much it moves 'tells' the camera the maximum aperture of the lens.
Todays' current crop of G lenses do not have this ridge or key. They communicate their specs electronically through the contacts inside the lens mount of the camera and the little 'BB's' or 'ball bearings' on the lens.
A pre-Ai lens, not having this notch in the mount, will push in on the tab on the camera before you can insert the lens far enough to turn it to mount it. Here's, I've taken my pre-Ai 28mm Nikkor and just set it on the camera, not applying enough pressure to damage the ring on the camera.
This is what will be damaged by forcing a pre-Ai lens onto a modern camera.... the Ai ring around the camera's mount.
Some DSLR bodies do not have the indexing ring, so they can accept pre-Ai lenses without damage.