jack rest cushion

[A440A@aol.com]

Jurgen Goering  writes:

<< I have in my care an Estonia concert grand about 6 years old.  It has a 
Renner action.  The jacks make quite a slapping sound when they hit 
their rest cushions.   Looking at the cushions, they 
seem fine - neither too thin nor  what I would call too firm.  Is this a 
common condition?   Will replacing the felt  punchings make a real 
difference? >>

Greetings, 
    I can't say about an Estonia, I have little experience with them. 
However, I don't remember having this problem with Renner parts in other brands of 
piano.  I would check the jack pinning, since it can contribute to noise, and 
also,  the hardness of the knuckles.  I have had several instances of noise on 
jack return that was ultimately due to hard knuckles. 
   Other than that, are the springs really strong?  If the hammer's rise can 
be felt in the key upon release, there may be enough spring force to create 
noise, regardless of the felt.  Maybe the first step in diagnosing the problem 
would be to make sure the spring is lifting the hammer gradually, and the jack 
pinning is firm enough to suppress noise.  
    On the subject of jack pinning, I have found actions that repeated as 
fast as any others, and the jacks were definitely verdigris'ed.  I was surprised 
to find this, but the jack doesn't need to be particularly loose to operate at 
full speed!  After viewing the high-speed films of jacks oscillating wildly 
under a hard blow, I have come to believe that 4 or 5 grams at the jack is 
perfectly acceptable, and may actually assist fast repetition by controlling some 
of the bouncing that the jacks does.  The Steinway that was doing well had 
about 8 grams of resistance in the jacks but still repeated as fast as I could 
hammer the key.  
Regards,  
Ed Foote RPT 
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html