Had some rattling on the front cyl. ('86 with 24k miles) and tried the Grambo-trick. But it wouldn't spin back as many rev's as I wound up. Tried several times but no luck. Dismounted, weaponed with Gypsy's drawing, a picture (was it Norm's?) and Clymer manual's special tool (also mentioned somewhere on this forum). Disassembled. Turned out that the washer was not present and the lowest 4 windings of the spring were off-set, giving the spring more or less the look of an L instead a straight cylinder-form. Prooving that somebody unfitted has been fiddling around. Anyway I managed to get the windings back in shape, made a stainless steel washer in a lathe and was ready for the reassembling.
Put one ear of the tensioner body in a vise, put the mushrum back on 1½ turn and preloaded the spring approx 4 turns (by turning the screw on the top end and the mushrum at the bottom end equally clockwise) before winding the adjustment screw totally (everything well oiled). Circlip on, and while holding the mushrum-end tight (to not let it unwind), replaced the screwdriver with the special tool. Installed, removed the special tool and it spins like new.
Did the other side as well. Washer present and everything in shape. Took only 10 mins.
Started the bike and the rattling was gone.
Alltogether an instructive experience thanks to all the great info from You folks on this forum.