I’m posting this reply to my own post as I’ve sorted the problem and someone with the same problem may find this in the future.

The 17mm bolt in the centre of the tensioner pulley wheel
http://i409.photobucket.com/albums/p.../Tensioner.jpg
was simply not screwed in enough. Simple as that! I’d guess it had been that way for some time.

That’s why the washer around it was loose and the tensioner wouldn’t operate. I turned the bolt several turns anticlockwise (left-hand thread). When it was fully tightened, further pressure released the tensioner and of course the washer wasn’t loose any more.


The direction of the belt makes the tensioner pulley turn clockwise – which will tend to loosen the bolt. So I’m going to be checking the bolt regularly.

On my car the tensioner is attched to the power steering pump, making removal of the tensioner a rotten job. But there you go.