Took apart my Shimano Acera derailleur cage to clean it up a bit and didn't bother to note the shape of the tension pulley which is a bit thicker on one side. It seems like it would be shaped this way for a reason since the guide pulley is symmetrical. Should the thicker side face toward or away from the wheel?
Edit: Here's a close-up showing an arrow or #1:
Per user in comment section, the arrow is indeed an indicator as to which way the pulley should be installed. See below excerpt taken from an unrelated Shimano derailleur model:
- Depending on the model, the guide pulley has arrows on it to indicate the direction of rotation. Install the guide pulley so that the arrows are pointing counterclockwise when looking at the outer side of the derailleur.
- The tension pulley has an arrow on it to indicate the direction of rotation. Install the tension pulley so that the arrow is pointing clockwise when looking at the outer side of the derailleur.