It's "Secured" (From rotation) by a Key fitted into the inset in the Crankshaft.
The only thing holding it onto the Crankshaft is the Main Bolt.
(#157 in the first diagram is what's causing you distress)
Details [Such as Mercedes deigns to gift us with] Here:
http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/03-3000hw.pdf
The "Lord ,Please don't let me Harm this fine piece of German Steel" parts are:
1.The sealing surface of the inner lip of the Timing Cover.
2.The sealing surface of the Crankshaft.
3.Almost anything to do with the parting surfaces of the DOWELS and the (Dreaded) HARMONIC BALANCER.AND their interface with the Nose of the Crankshaft.