I had to remove my tensioner, so I just went out and did it. The first allen cap is a 12 mm. This allows the spring to be removed. The second, or internal is a 12 point threaded ring that can be removed with a regular hex 17mm allen key.
Disassemble by pressing the pressure pin out of the larger body. Then clean the parts. Put the outside housing back into the bore. Screw the threaded ring back into the bore.
Inserting the pressure pin into the housing is OK at this point, but do not re-insert the spring and put the cap back on without a chain installed.
'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)