OK, here's what Larry said:
The ratcheting tensioners have a number of teeth along the side of the plunger. There is a pawl that catches on these teeth as the timing chain wears. This pawl holds the tensioner in place even after the oil pressure is relieved from the plunger.
The tensioners in the 616/617 does not have this, it really only fully tensions the chain when oil pressure is applied. This means it is slightly loose at start up. I think the detent just keeps it from completely loosening when oil pressure is not present. It does not continue to tighten and maintain tension as the chain and associated parts wear, as does the ratchet.
With the ratcheting tensioners of the 103 and 104, you have to push that plunger all the way through and reinsert it in from the back. This gives enough slack to put everything together, then when the engine is started, the plunger will ratchet as far as the chain will let it go, finding its tense position.
OK. Now go read these two sections of the service manual, for the OM617, and the M103:
http://www.meimann.com/docs/mercedes/Tensioner_M103.pdf
http://www.meimann.com/docs/mercedes/Tensioner_OM617.pdf
The description for both is identical. And the OM617 tensioner DOES need to be removed in direction of travel, and re-installed from the other side. I'm sorry, but Larry was incorrect in his original statements... I'm not calling myself an expert in mechanical knowledge, but the Mercedes factory service documentation speaks for itself. Make sure you read both carefully... the OM617 document has more useful information, the M103 is pretty, umm, concise.
To properly do the OM617 chain replacement you should remove, and "reset", the tensioner. I believe that is specified in the factory procedure as well.
Best regards,