Tensioner never replaced. Belt 1000 or so miles ago. The fact it only happens when warm sounds like when the belt gets hot it expands and comes a bit too loose. I could be talking nonsence here though.
The tensioner is spring loaded, and from memory, a spanner of 15mm is needed to push back the spring. Then, you can remove the belt. BTW, some tensioners have a couple of holes which line up and you can fit a long 4mm bolt through it or similar to lock it. If not, you may find that 2 people are needed. One from the top to move the belt, and one from underneath (after removing the o/s/f wheel and splash shield in the wheelarch which keeps the engine pulleys clean) to work the spanner. Fiddly, but not hard.
Before removing make a careful note if there are any spare vees on any of the pulleys, and remember to fit the belt excatly as it was fitted before otherwise it will be noisy and wear the belt prematurely.
The easiest way I found was just to unbolt the tensioner from the engine.
It sounds like it will need to be removed for replacement anyway.
The new one is then bolted on the new belt fitted over the pulleys and the tensioner levered over anticlockwise against it spring. The bolt at the top is Left hand threaded so it wont unscrew when you lever over the tensioner with the spanner.
The fixed tensioner also has a 15mm bolt in its center, and you will need a recessed spanner to undo it. There isn't enough space to get a socket in because of the chassis, and a regular spanner won't be recessed enough.
Hi. Sorry to be a little off topic, but I bought this aux belt pulley with slightly smaller diameter and I want to change it. 156 lighten crank
If I remove the aux belt as described here, the pulley is held by 4 screws that will be presumably tightened with high torque, am I right? Do you think I will be able to change it at home? Do I need to lock the engine somehow (in gear??) not to turn the crank when unscrewing the bolts? Or is it a simple job and it is just me expecting difficulties?