If memory serves correctly, you should jack up the car under the lower a arm so the suspension is loaded, then check for free play, preferable with a pry bar under the tire. I forget what the allowable movement is. 1/8" to 1/4" or so.
Like Todd said- don't confuse wheel bearing play with the kingpin.
And if they don't take grease (Like Jerry said) you can usually heat them up to coax the grease in.
Personally, I wouldn't change them unless they were real bad.
When I was a kid, my first car was a 48 Plymouth that needed king pins. If I hit a bump, the front would start to shimmy so I would hit the next available pot hole and that would usually knock it back in line. Then I put my snow tires on the front. That worked well enough until I got my next car.
The next opportunity I got to do kingpins, was on my 1952 Dodge pickup and what a pita that was. One side was fairly easy and the other, busted my chops.