The king pin was already down 1/8-3/16 before you started and you didn't see that? Maybe? and you haven't moved it at all? Zerk at top and bottom, lock pin in center? Right? Zerk holes, Zerk removed, would be a good place to apply penetration oil?
If it's a solid pin and you say it moved down, the bottom has to move also or it is 1) cosmic radiation thermal interpolation. Never seen on planet earth. 2) you bent/broke something, 3) you are wrong.
But I never worked on a AD king pin so 4) I could be wrong. Agreed, that is the least possible.
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0302.htm
