I have 2 blackbirds.
 

I have 2 blackbirds. The very 1st 1996 and a 1998 both mk 1. This morning the 1998 started to rattle like a biscuit tin full of ball bearings. Checked the forum for ideas. CCT seemed to be issue. Stripped it down and found it was the issue. However I could not see why. So I stripped the other 1 down. Both looked the same and seemed alike. Then I noticed the spring that did not seem to do anything inside the tensioner body. Comparing the 2 the problem was obvious. The top of the spring that goes into the slot on top of the threaded part was broken off and stuck in the spring itself. I warmed the top part of spring about 7 mm from the end. Put it back with some tension on it. Put it all back together and tried it. Took it out for a good long run and gave it some stick. Perfect. So if anyone has tensioner issue check that first. It will save you between £60 & £100.