Adjusting the Bosendorfer Cheek Block

Bosendorfer pianos can seem a bit mysterious to technicians in the U.S. I know I don't see very many. They have some unique features like double flanges damper blocks (they hinge front-to-back and left-to-right). They also feature cheek blocks with capstans. One on the front facing down and one in the rear facing back.

First you need to make sure that the glides are bedded, which could be a whole article unto itself. If done properly the front should knock at key 1 and 88. The cheek block's down facing capstans are intended to put just enough pressure on the front rail at those point to keep them from knocking once the cheek blocks are tightened. The rear capstan is to put just enough pressure on the key frame to snug it up against the dags but still letting the frame shift smoothly.

With a capstan wrench, adjust the front capstan so the front rail no longer knocks when the cheek block is in place and tightened. The rear capstan is the same idea but instead of looking for knocking, grab the stack gently pulling the action front to back. The rear capstan should be adjusted so that there's no play as you pull on the stack. Be careful not to over pinch the keyframe so that the action shift is affected.

I should've taken photos of the cheek plates. They're unique as well.

If you have some experience with them, leave it in the comments.