Repetition Revisited

[A440A@AOL.COM]

Lance writes:
<< <<After the key is depressed and only partially raised (1/8 inch?)
for the next blow, upon the next key depression the hammer gets wedged
against the backcheck and blocks.  >>

Greetings, 
   Nothing affects repetition speed as much as checking height,  but 
catastropic failure of the action to reset is usually caused by a combination 
of other factors,  masking each other and playing hob with us Steinway 
Sherlocks.  Here are the things I would check. 

1.  Let-off or drop too close! This often will allow the strings, under their 
maximum excursion, to hit the hammer as it comes up for a second note. When 
this happens, the force drives the hammer past its normal checking height and 
the backcheck grabs it far too low to allow the jack to return. 
     1a.  Those extra strong springs may be tossing the hammer into the 
strings,which will cause the hammer to be sent down in a hurry.  Any spring 
strength beyond what it takes to raise the hammer smoothly from check is 
usually wasted, and it makes escapement a lot more resistant. Try moving the 
let-off and drop to 1/16"(in the middle octaves) and softening the spring so 
that the hammer lifts as fast as possible without being felt in the key. 
2.   distance between rest felts and hammershanks.  If it is 1/2" or more, 
you are asking for repetition failure. 
3.  Low or non-existant checking.  Make sure the jack isn't binding between 
the knuckle and backstop pad on the balancier. 
4.  Loose balancier pinning
5.  Dented or hi-friction grub,( the slot the rep spring rides in, under the 
balancier)

Good luck, 
Ed Foote RPT