when you are at TDC, the most that the valve would move downwards is about a 1/4 of a inch. I had plenty of room to compress the spring and be able to drop the keepers in place. Actually, turning a cylinder to TDC on one head would also set another cylinder to TDC in the other head, so you can actually work on 2 cylinders(one at a time) with one TDC turn. I used a plastic piece of stick to push( on the metal sleeve) the seals down in place. I realize that having compressed air to keep the valves up would make it a lot easier to put the keepers back in, but in my case, it worked just the same. I just made sure that the car was secured not to move. Battery was also disconnected.