Assuming the same as the Rover 25 - it will be - changing the aux belt is pretty easy and straightforward. There is decent space between the engine and the inner wing
This. Quick easy job, even on a MGF.
That's told me.
My other problem was, even with the tensioner pulley fully retracted, I struggled to get the new belt on the pulleys. I had this once before with an Omega auxiliary belt, I swear it was too short, and I never used it in the end. I know belts stretch, but there is not that much slack with sprung tensioners.
Are you using a long spanner or ratchet on them? That usually gives plenty of slack to get the belt on, which is tricky with standard length tools. The other thing to do is to fit the belt to all the ribbed pulleys first, and slip the back face onto the smooth tensioner. This requires less movement, and saves the need for an octopus.
Thanks Nick, several good tips there. I removed the outer (power steering) belt easily, locking the tensioner with a pin through the hexagon. It was trickier rotating the alternator belt hexagon, with a long spanner things got in the way, and a short spanner lacked the leverage.
Haynes does a wonderful job explaining things concisely, ' To hold the tension pulley in this position, fit a locking pin (max 3mm diameter) into the hole in the backplate, against the stop on the tension pulley.'He adds drawing 5.50 to clarify things, but in vain. Holding the ratchet with one hand I could not see where to insert my pin.
Next time it will be easier. I imagine Astras are similar.