The most important and also the most costly mistake made on these tensioners is that they have to be RESET. They have a ratchet locking mechanism in them that prevents the tensioner from releasing tension as the chain wears and when the engine is not running ..this is to prevent the chain jump so common on the older systems at start-up. [ chain rattle]
So, you have to push the pin all the way thru and re-enter it from the front any time it has been dismantled ..failure to do so can cause cams to snap right in half and chains to snap. See even experienced mechanics make this tragic mistake.
http://mb.auto.pl/wis/w124/CD01/Engine/104/05-3100.pdf