The derailleur pulleys position the chain precisely. But as they wear out, they must be replaced..
To unscrew the derailleur pulleys, you often need a 3 mm Allen wrench. We added a 4 mm for « troubleshooting ». This operation is possible on the bike or derailleur disassembled as here. It is recommended that you take advantage of a chain replacement to perform this operation.
Pictures © Frédéric Iehl
Time and difficulty
It will take you about twenty minutes to perform this operation. You will also need some force in your hands to « hold » the derailleur in the right position. The difficulty is average.
We unlock the upper pebble. Half a turn is enough.
The lower pebble is then unlocked. The screw is removed and then the pulley.
We then move the outer face of the screed and unlock the second one.
Here is the comparison between a new pebble (green arrow) and a used one (red arrow). The teeth are very sharpened with wear.
Pulleys can have a sense of rotation. Or a low and high positioning. So you have to look at them properly.
In blue, there is the path and the direction of the chain. In green, the direction of rotation of the pulleys. Which therefore follows that of the arrows that adorn them.
We begin to place the upper pebble in the right direction!
The upper pulley screw is firmly tightened.
Then place the lower pulley in the right direction
And we block the screw.
We put a wrench back up.
It is imperative to block these screws. In use they can be unscrewed and in this case the pebbles will be lost on the way… So block them well!
If the threads are damaged, you can use tip holder nuts or shim screws. On the other hand, a nut will have to be provided.
Still prefer a screw with a fairly flat head.
We will put behind a nut that we will tighten very tightly too. A small stroke of file will reduce a screw that is too long.