action reg puzzler on M & H BB

[A440A at aol.com]

<<  under continuous mf - ff blows, as in tuning, after anywhere from 1 to 10 
strikes (letting the key all the way up), the hammer will get caught on it's 
way back up by the back check, thereby not allowing it to strike.

 I have tried numerous adjustments to the angle of the back check as well as 
to the height of check for these 3 notes, to no avail.  Everything seems to be 
identical to the surrounding notes, including jack reg - both in the window 
and to the knuckle core -, rep spring strength, key dip, stroke, the arc of the 
tails, let-off, drop, etc., etc... you name it.  Keys are rebushed and moving 
freely. >>

  If the hammer is getting caught by the back check on the way up, that means 
you are probably probably hitting the key before the jack has a chance to 
reset under the knuckle.  Some reasons for this are 
  1.  Pinning?  If your balancier and/or hammer pinning is too loose, you 
will not have enough spring strength to consistantly reset the jack.  
  2. Aftertouch?  Too much and the action can lock up
  3. Something is maybe stopping the jack, itself.  Make sure that the end of 
the spring is not digging into the near side of the clearance hole in the 
jack. Or, make sure that the entry angle of the spring into the jack is not so 
mis-aligned with the hole that it is sometimes jamming as the jack trys to 
rotate.
  4.  Proximal side of the knuckle may have some irregularity which is 
occasionally interferring with the jack return. 
   5.  It may be helpful to change the whippens around to see if you can 
isolate the cause.  If the problem remains with a different whippen, at least you 
will know where to stop looking for the problem?  
Good luck, 



Ed Foote RPT 
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html