- The balance rail key pin' was lightly shifted to the right as well. Sometimes, since the production of the upright piano, the balance rail key pin has not been centered to the specified position, causing a slight offset. As a result, when a key is pressed, the balance pin gets wedged against the cloth edge of the key's hole cloth bush.
In this video, we visually observe that 'the front rail pin' has shifted. There is a significant friction between it and the hole of the key bush.
Here's how to fix it:
1 Remove the keys (D#), as well as the neighboring (D) and (E) keys for convenience during the procedure.
2 Using pliers, gently rotate 'the front rail pin' so that its top edge becomes in parallel to the key's outlet.
3 Install the key (D#) back in place and test it. Also, install the neighboring keys back. Make sure that the key (D#) has smooth movement and does not get stuck now.
https://youtu.be/YeXPnjszRaY
Good luck!