In changing a cam and a rocker arm, I inadvertently pinned the flywheel wrong. On the M70 engine Top Dead Center is set by putting a dowel through a small hole in the engine block and lining it up with a small hole in the flywheel. The problem is that there is more than one hole in the flywheel that will accept the dowel. While the "wrong" holes are a little larger than the one made to set TDC, I still messed up and used one of them. The result is of course that I bent a valve when I bolted the cams back on.
Make sure the relief in the toothed crank pulley is at 5 o'clock for TDC.
Since you can't see the marks on the crank pulley when the engine is in the car (it is even hard with a camera tool) the safe way is to make sure you are at TDC, is to look at the crank pulley and note the area where there are no teeth. The pulley teeth are what tells the ECU where the engine is in its rotation and the area where there are NO teeth should be at about 5 o'clock - if the dowel pin is in the flywheel and the "relief" area of the crank pulley is at about 5 o'clock, then you are at TDC.