How to collapse new chain tensioner for install? M117
 

I cannot get this piston to go in far enough to install it. Brand new MB tensioner. I read somewhere it contains a ratcheting mechanism? How do I put it in?

https://i.imgur.com/9oqEhU2h.jpg

I have long 8mm bolts with nuts on them. install the tens. with the long bolts, thread the nuts against the tensioner until it's tight on the block. remove 1 long bolt, install the correct bolt. repeat. haven't done 1 in 10 years or so, the dozen or so chains I did, never failed. always oe tens., also. good luck, chuck.