Deidre Dixon's question [150612 MMDigest] about leather type for the
Ampico primary is good as it is seldom mentioned on MMD.

Usually leather of about .035 inches works just fine.  A chest on my
work bench now has original .035 inches for both inside and outside
facings.  If the leather of the inside portion is too thick, the valve
will be restricted in movement.  Thick leather will cause the inside
button to touch the pouch while the valve is at rest, and that may
cause leakage due to improper outside valve seating.

The best rule is to carefully measure the thickness of the original
leather and match that during the rebuild.  Beside the thickness of
the inside valve leather, another parameter must be observed.  The
thickness of the gasket material used on the primary chest will affect
the pouch dip and/or the valve button to pouch clearance. Again,
match the original gasket.

Primary valves should be a very smooth, tight suede.  The primary
chest can be a huge source of vacuum loss if the outside valves leak.
Since the weight of these valves is so small, a precise, flat fit of
the outside valve facing is critical.  Inside facings are less critical
to vacuum loss since that leakage only becomes a factor when the valve
is on.

After rebuilding, the primaries should be spun in one direction to get
the nap to lay down.  They should be gapped at .035 inches or much less
at .020 inches.  This smaller gap can create problems as any tiny
debris, if present, cannot escape the gap.

Primaries are easy to rebuild, but critical to good performance.
Thoroughly test them before putting them back into the piano.

Bob Taylor
Missouri