U1 hammer butt problem

[Roger Jolly]

>
>>
>>I recently re-flanged my U1 due to bobbling hammers caused by the silk 
>>thread which holds the hammer butt spring being broken on about half the 
>>flanges.  Since that day, I have a new problem with the piano: the jack 
>>gets caught under the hammer butt on rapidly repeated notes and blocks 
>>the hammer to the strings.  This happens on about 10 to 15 hammers in the 
>>middle of the keyboard.
>>
>>I checked the backchecks and the hammers are checking at 5/8".  I checked 
>>the lost motion and there was enough to allow the hammers to move back 
>>with the hammer rail when pulled away from the strings.  There is enough 
>>dip to allow the jack to letoff.
>
Greetings,
                      Do you have sufficient after touch?  If the hammers 
have been filed, and the back rail has not been corrected, (46mm blow if my 
memory is correct).  This can be the cause of the problem.  Dip should be 10mm.
  Key level through the centre section will also give the same problem.
Are the length of the loops the same as the old loops?  This can 
significantly alter the spring tension.
Did you file and mate the hammers to the strings?  After changing the 
flanges, the string groves will never quite line up with the strings.
Just some extra thoughts.
Regards Roger