Bobbling Hammers and Tight Key Bushings on a Yamaha

This piano has hammers bobbling on the strings. The front key bushings and balance bushings are tight causing keys not able to return or bounce back up. 

The first picture shows when the key is pressed all the way down, the hammer is still very close to the strings. The non-fully-returned hammer bobbles on the strings. The second picture shows when the key is fully pressed, the jack is still under the hammer butt, pushing the hammer close to the strings and bobbles. The third picture shows a jack under a hammer that is not bobbling. The jack rotates out of the hammer butt when the key is fully pressed down. The jack to hammer butt gap shall be about 1-2mm. The key dip or aftertouch needs to be increased.

The quick solution is to reduce total front punching thickness shown in the first picture. But note that the keys are not very level. If the customer has budget to have the problem properly solved, the balance rail can be raised with shims to increase key dip/aftertouch, then the keys re-leveled and re-dipped. 

For the tight bushings, there are easing tools for this job. Insert one thin tooth into the mortise/hole, squeeze the wood to enlarge the hole and compress the bushing felt. Sometimes the balance holes are tight, too. A balance hole easer is needed here. But be really careful not to enlarge the balance hole too much, then the keys will feel lucy loose or loosing control.

The partial front punching reduction is done while tuning, about a dozen keys needed it. The key easing took about an hour. The total service time including tuning is 3 hours.