I'm going to change the valve seals on a D16y7 engine without taking the head off. If I do this will the valve drop below reach with the piston at TDC??

 

If you decide to change the valve guide seals without taking off the head at the TDC the valves might fall into the block because two of the pistons will be at the bottom.

This is what I would do. I have tried this once and it worked for me. I am NOT saying this is the correct way, but I hope it helps you out.

1. Take out all the spark pulgs.
2. Put your oil dip stick in spark plug hole in number 1 cyl.
3. Using a 17mm socket (I think that is the size) turn the crank pully (clock wise).
4. The dip sick will move up and down because you are moving the piston
5. When the dip stick is in the up position the valves will be closed and the piston will be at the top position to insure if the valves fall you will not be in trouble.

Repeat process for the other cyl's

Good luck and I hope this helps you out!!!!