1997 E420 noise help needed
 

when i started the engine i hear a tacking sound what i thought at first the cams are worn but i took the rocker covers off and every thing looks normal then i thought it could be a dead valve please is there anyone out there that can let me know how to check for dead valve

The common issue for the sympton you describe is a defective oil delivery tube. Oil is carried from the intake lifter to the exhaust or visa versa by "U" shape plastic tubes. For some fool reason these tubes were built with a hole at the corner of the "U" that was filled with a glued in plug which falls out and keeps oil from the affected lifter. The problem is easy to see if one knows where to look.

The affected part is number 119 180 02 66. See attached picture.