Good evening,

The top of the little clutch switch lever on my rear mech (XT mech on my Whyte T-129) touches the frame when I move to the smallest sprocket on my cassette. This effectively stops the mech moving all the way in and from selecting this gear (the chain remains, stubbornly, on the second sprocket).

Oddly, if I move the mech’s clutch switch lever to ‘off’ the mech can move past the frame and select the smallest sprocket (because the offending clutch switch lever has been moved off to the side). I should also mention that this happens whichever front ring I’m on. Other than this, the bike switches fine.

I’ve a dark suspicion that the solution might involve something called a ‘b-screw’, but I’m really not sure. Can someone advise?

appreciated

sc

Tightening the B screw should move the mech away from the frame

Should be quite clear that the mech is moving down as you toghten it, you can see which one in the pic below

HB has it, I had some issue with a M109 frame. B screw needs to be almost fully wound in. You will see the mech pull away from the cassette and clear the horst link.

Dont go mad with it, just make sure that the jockey wheels aren’t miles away from the sprockets otherwise your shifting will suffer.
Ideally they should be just above the sprocket rather than squeezing the chain onto it.
In your case its more important to clear the frame firstly though.