I have heard mention of these ratcheting tensioners before. I believe the cure for your dilemma is:

1. Remove cap and spring.
2. Push tensioner plunger out in direction of tension (would be toward chain)
3. install tensioner housing on engine, insert plunger, then spring, then press cap into place over spring and tighten cap. (tensioner should ratchet itself out to proper preload on chain as you squeeze spring.

If anyone else knows something I forgot, chime in, but I'm pretty sure this was the procedure I'd seen.

-Chris 80 240D w/617