as it happens i repaired my tensioner the other day!! ok its not the puley that is the problem nor the arm its the damn spring loaded tensioner, what happens is the plastic around the top and bottom eyes wears, this allows the finite movement of the spring to lose its tension as its almost fully extended when the plastic wears!!
I made some bushes out of copper pipe cut in half, and inserted them under the metal eye on the bottom one and on the top of the one on the top this has the effect of taking out the play in the plastic and it now works properly again, dont know how long it will last but i know i did it at least 2 yeatrs ago with just the bottom eye as i found the piece of copper that had worn thin in there!! lol
HTH 
didn't we replace one on yours not so long back, or was that hers?
btw, want a turbo and/or fanifold before they take a trip to Ardley's big hole in the ground?
yes yes and yes!!! why didnt you remind me last time i was at yours!!! oh i rmember you were on a conference call, :-Xwill definetly pick it up next tiem i am there!!!