The whole thing takes less than 1/2 hour, but, if you mess up, you will damage the engine. The reason is fuel will leak into the cylinder in liquid form. Because liquids are not able to be compressed, when you turn the starter, you may bend a rod.
The could only happen if adjusted incorrectly, but I have seen a pro do this the wrong way!
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS