[Licensed to kill]

So, I'm just checking everything on my engine to make sure that settings are correct and was checking the ignition timing. Found the point a tad tight so set them to .020 but noticed about 5-10 degrees of free movement in the cam when turning it with a screw driver on the locking screw. Everything under the cap looks new but this movement in the cam doesn't seem right. How can one ever set the timing and keep the timing right if the cam is free to move back and forth several degrees?. Theoretically the rotation of the engine should keep it all the way over one way but should t not be free of any advance/retard play??. Also, could be related but I find very little difference in full retard to full advance on the lever as far as how the car runs. Lots of movement on the plate but would expect a more noticeable change in the engine for the amount of timing difference.