Action Inspection
by Steve Woodyard

Key Inspection

Key pedestal felt
Remove the keys and inspect the pedestal felts. The felts should not show any extreme signs of wear. Sometimes the back "knife" edge of the hammer digs into the felt and creates a "worn out" line across the back end of the felt. This will cause performance problems. If the wear is not too severe then the felt could possibly be re-fluffed using a felt picker (piano tech tool). Otherwise replace the felt. After the repair or replacement, saturate the felt with an acceptable silicone spray. Allow the propellant of the spray about _ hour to dissipate before re-installing the keys.
For a time the Key pedestal felt was changed to a white felt and was installed on the hammer curve instead of the pedestal. The action modification listed in the service manual discusses the removal and pedestal re-installation. It does not address failure of the white felt due to wear. This wear can be accelerated due to the rough nature of the bare wood key pedestal. Replace the damaged felts or perform the modification.

Damper Inspection

With the damper screw or screws removed, the damper or dampers, except for the pad area, should be straight or flat. The angle of the damper mounting portion of the action rail creates the angle necessary to give the damper the appropriate tension. In the older models (1969-73, etc.), the established tension caused by the action rail angle might not have been adequate for some lower notes if the performer required aggressive damper action (quick stop of the note).
The longer the tine, the more the force or pressure, is needed by the damper, to stop the tine motion. The amount of force needed also depends on how aggressive or quickly a performer wants the tine stopped or reset for the next strike. Quick re-striking or fast repetitions require more aggressive dampening to produce repeated clear notes. Because hitting or striking a tine while it is at the top of its swing or on a portion of the down swing, will cause some note cancellation (thunk sound similar to a misaligned strike point), damper response and adjustment is important to sound performance.
In the modular variation, the damper tension is created by varying the width of the aluminum arm, in the tension area. The tension area is the portion of the damper arm between the mount to the action rail and the bridle strap tongue. As the need for tension from the damper lessons, the tension area is weakened by being notched out. As the tines get shorter the notch gets larger. The bass notes are shorter and have no notch.
On the older versions (1969-73) the dampers are individual and have no notches. The bass note tension is increased by the addition of a triangular shaped molding, under the damper, near the action rail mount. This shortens the tension section and increases the tension. In some respects this amount of tension was still not enough and some performers had a reverse bend put in the damper at this area to further increase the damper tension. Note that this also increases the touch sensitivity or heavy feel at the key. These notes take more key pressure to play. So, if you have an older model that is heavy to play in the bass area, take a look at the dampers.
Damper length also plays a roll in damper action. The more the damper contacts the tine near to the tine end, the more successful is the dampening action. Unfortunately as the tine swing is greater, as it is on the bass notes, the ability to contact near the tine end is offset by the required down movement distance needed by the damper so it gets out of the way of the tines first full down swing. Otherwise it deadens the note. A compromise on length exists at the bass end of the notes.
On the modular dampers the length is pre-cut, on the older individual models, the length for the bass section was originally longer then needed. Many techs have cut these dampers _ inch shorter.
Note: The Mark V version has one more added feature to its dampers. The portion between the tension area and the pad end has formed bends along the edges. This minimized whipping of the damper and improved the aggressiveness of the damper response.

Action Rail Inspection

This will require the temporary removal of the harp and the support blocks. There are four basic designs of action rails utilized during the 70's and 80's. The wooden action rail and the aluminum action rails. There were three different aluminum designs but their basic functions were the same so they will be discussed as one. The differences were related to how they mounted to the keybed.

Wooden Rail
The wooden rail (late 60's, early 70's) was 2 pieces screwed together as one. The rail height varied due to the assemblers installing various shims between the action rail and the keybed. The higher the rail, the lower the hammer sits off the pedestal and the longer the hammer has to swing to strike the tine. With the key pressed down and the hammer in the up, lock position, the back "knife" edge of the hammer cam curve should be about 1/16th of an inch from the back of the key pedestal. This setting is normal an all ages of pianos and more critical on any piano where the pedestal has a bump or marcel curve. If the hammer to key pedestal setting is off, it causes the action to feel not as responsive.
The intent is for the hammer to roll over the pedestal curve or bump, on the upswing, strike the tine as its hammer rocks on its rear knife edge, which causes it to snap back to its up rest or lock position, which places the cam curve just barely in contact with the pedestal curve, marcel or bump. It should be noted that the longer the hammer swing, the greater the dynamic range of sound that will be produced. It also will cause a slightly heavier feel to the touch sensitivity. The Mark V has a long swing and the balance rail was moved plus the pedestal and hammer cam curve were changed to affect the touch sensitivity. Also a longer hammer swing will cause an increase in broken tines. Many feel that the negative side of the longer swing is worth the extra "Bark and Bite" sound that is achieved.

Aluminum Rails
The aluminum rails were mounted without shims to the keybed so, their height was consistent piano to piano. Their locations were predetermined by screw hole locations so most of them were mated to the pedestal with reasonable accuracy. But, there could be some minor misalignment, so it is worth verifying the hammer to pedestal setting.
Any removal and re-installation of the action rail will require the proper alignment. The pedestal to hammer alignment was mentioned in a previous section of this article. The action rail, left to right alignment will be noted as a compromise. Each hammer does not always sit perfectly on top of each pedestal. The best way is to insure that the two end notes (#1 & #73) are as best aligned as possible and that no pedestals contact any hammers other then the intended hammer.