I recently did some work on the Yamaha Grand at Penticton Alliance Church. I removed the action (the mechanical unit inside the piano that includes the keys and hammers) and brought it to my shop. I removed all of the old hammers, installed a new set of hammers and did a full regulation (adjusting all of the moving parts so they are operating properly). Old hammers develop a flat hard surface where it strikes the string creating a harsh bright tone. New hammers are softer and have a full dynamic range. Here are a few photos from the process.