300e timing chain tensioner
 

I am in the process of changing the upper timing chain cover seals in my M103. I had to replace the three bolts that hold the timing gear on. I had to pull the gear off (chain still around it) to retrieve a small piece of metal that had fallen in. The tensioner is so tight now that I cannot get the gear back in place. How can I loosen this enough to slide the gear and chain back into place and do I need a special tool?

The tensioner is a ratcheting device, cant go backwards. Have to pull it and reset it. Gonna need a 12mm allen and a 17mm allen to get it out.