Ok so looking at the tensioner pic, what happens if you disconnect the cable, the tensioner should only have the spring tension on it?
Yes, thats right - but then with the correct belt in place (and the M36 thats shown in the picture IMHO can't be the correct belt as it's just incredibly tight) - but then how do you engage the drive or stop the drive - as you can't have both at the same time.
I would personally be doing what someone has obviously done on the red one - get an angle grinder and take a bit off the tensioner
Well spotted - that said I am not sure exactly what that would help - as mentioned that image has an M36 belt installed and it was far too tight to be useful - you could not get the tensioner arm to even move a couple of mm at most and it certainly didn't add any 'tension' to the belt. With the two old and unknown belt sizes, when you engage the drive - the tensioner arm moves out quite a lot and adds a lot of tension to the belt.
So if one did cut off some of the arm that'd do nothing - not to mention that the idler pulley is just about the same width, so you'd just have the idler pulley rubbing or perhaps even worse not being able to turn as it was against the raised bit of the chassis.
