Are you installing a new tensioner? Or did you not compress the spring and insert a drill bit (or something similar) into the rod to keep tension on the spring?

Either way it sounds like you need to get the spring and rod back in place on the tensioner. I have a pair of very large adjustable pliers that open up enough on one of the settings to squeeze the spring and rod against the tensioner. Once it is squeezed enough to insert the drill bit and hold it together you can mount that assembly to the front of the block.

It will probably take several attempts and perhaps having someone who can help by putting the drill bit into place once you get the spring compressed would make it easier.

Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal