W. Deane Wiley wrote:

    "When the hammers are resting on the top back of the keys, how much
    play, if any, should there be between the back of the hammer and
    the top of the wooden button attached to the wire coming from the
    pneumatic?"

I'd like to start by saying that I know of no modern Aeolian player
that has the striker pneumatics connected to the keys.  In all of the
modern Aeolian players, the striker pneumatics strike the underside of
the keys via a wire and a wooden button, which are connected only to
the striker pneumatic. The wooden button hits a piece of felt which is
glued to the bottom of each key.

In essence, there is no way to answer Mr. Wiley's question, because the
wooden button at the back of the key is not connected to the pneumatic.
It is connected to the wippen in the piano action. (More accurately,
the button is screwed on to a wire which is also screwed into a wooden
elbow at the other end.  The other end of that elbow is connected
to the wippen.)

The only Aeolian players that have the button at the back of the key
are the players with a drop action (where part of the piano action is
below the keybed).  The buttons are used to adjust out the lost motion
that occurs as a result of using the piano, i.e. from wear.

Removing the lost motion between the striker pneumatics and the keys
is, for all intents and purposes, accomplished by raising the stack.  I
will be creating yet another web page at Player-Care.com to fully ex-
plain the details involved in properly making both lost motion
adjustments.  However, with regards to the lost motion adjustment in
the piano action, the correct answer is "almost zero."  And, since
I realize this is a subjective answer, let me explain.

As with any drop action (or upright for that matter), adjusting the
lost motion to zero is asking for trouble.  The main reason this is
true is because the wood might swell due to an increase in temperature
and/or humidity.  If that happens, the jack will not be able to get
back under the butt quickly or fully.  Should that happen, the jack
will not be resting firmly under the butt, and the power for striking
the key will not be transferred from the jack to the butt properly.
This possible problem is even worse in a drop action than in an action
that rests above the keys, because of all the extra weight and angular
changes in the drop action.  Another way to say it is that the keys are
pulling the wippen up as opposed to pushing the wippen up.

That being the case, it is wise to back off the lost motion adjustment
in a drop action by a few thousandths of an inch.  This is best accom-
plished by turning the button clockwise until the hammer just starts
being pushed away from the hammer rail.  Then the button is turned
counterclockwise until the hammer comes back to rest on the hammer
rail.  Then the note is struck firmly a number of times to set the
button back in its hole.  After that, the back of the key is depressed
by hand to ensure that the hammer is indeed resting on the hammer rail.
If it moves even the slightest amount, turn the button further counter-
clockwise until nothing happens when you depress the back of the key.

Next, touch the front of the key ever so lightly.  If the hammer moves
with the slightest of pressure, the lost motion adjustment is most
likely too tight, too close to zero, or even at zero.  When correctly
adjusted, there should be a very slight sponginess to the feel of the
key.  And, if you watch the piano action from above while touching the
front of the key, you will see the back-check move ever so slightly
before the hammer starts moving.  This indicates that there is a very
small amount of lost motion between the jack and the butt.

Lastly, when correctly adjusted, only a trained technician should be
able to tell that the lost motion exists.  It should not be noticeable
to the pianist.  If it is noticeable to the pianist, the adjustment is
not tight enough, and further adjustment is needed.

Musically,
John A. Tuttle
Brick, New Jersey
Player-Care.com