Borbin the 🐱

In 1977, Nikon started using the automatic indexing of the lenses. This replaces the manual indexing done before by alining the metal fork on the lens with the camera pin.
See this great article about the Nikon evolution.

This is a original non-AI lens mount of a NIKKOR-H 300mm f/4.5:

Nikon provided conversion kits to convert lenses before 1977. According to the Nikon Lens List, this lens is from 1970 and requires the conversion kit #53.
I only found #52 in a camera store in Finland, which is for a newer model of this lens.

The kit #52 differs from #53 that the screw to connect to the aperture lever is not used anymore and replaced by a notch in the aperture ring at the same position. To make #52 work with this lens, a small hole is drilled and tapped to use the original screw:

The lens mount is unscrewed and carefully pulled out:

The screw for the aperture link is M1.7x0.35:

And connects to the lever on the inside:

The 1.5mm hole is drilled at the notched position in the new aperture ring from conversion kit #52. Ideally the hole should be 1.35mm for a M1.7 thread but the 1.5mm drill was the closest I had and for this purpose good enough:

The hole must match the position of the original lens ring:

The other difference between kit #52 and #53 is that the aperture click notches are on the opposite side:

The aperture click spring needs to be moved. To get the correct distance, a non stretchy tape like 🦆 tape, is used to mark the position:

From the start of the first screw to the correct position:

This is the position for the screw hole:

The screw size is M1.4. For this thread size, a 1.1mm for the thread hole should be used, but I don't have those drill sizes, so I used the 1mm as it will work too since it is soft Aluminium.

Attach the aperture click spring at the new position:

Add a little bit of grease to the inside the Aperture ring and put it on:

The new AI converted lens mount for the NIKKOR-H 300mm f/4.5: