I use the following method to easily and quickly achieve factory-perfect replacement of vertical damper felts with no follow-up regulation required. It is essential, however, to carefully match all dimensional aspects of the new felts to the originals, especially the position of the backing-strip to mount to the damper block. If necessary, remove the mounting strip carefully with a razor blade and reglue in the exact position as the originals.

1. With the action in the piano, use a white china pencil (available at stationery and art supply stores) to mark the end strings of each section at the top of the damper felts.
2. Remove the action from the piano. Using a straight edge, connect these guide markings on the strings with the china pencil. The clearly visible white line across each section precisely represents the top of the original damper felts. Make certain to indicate any deviations from a straight line, such as the rise on the lowest tenor dampers on some Yamaha consoles, etc.
3. Install the action horizontally in an action cradle, with the dampers facing upward.
4. Pull all the old damper felts off the damper blocks. Use a Moto-tool with the drum sander attachment to remove any remaining felt and glue from the damper blocks.
5. Re-install the action in the piano.
6. With the sustain pedal depressed, squeeze some glue onto the mounting strip of a new damper felt, and slide it down the string into position so that the top of the felt is perfectly aligned with the white line. Release the pedal so that the damper block contacts the glued felt. Proceed to do the same for the entire set of new felts. If the new felts are an identical match with the originals, no regulation whatsoever will be necessary and the installation will be visually and functionally perfect.

The small white markings on the strings can be easily removed by lightly rubbing with a soft, dry cloth.