"Bobbling" hammers on a new Yamaha U3. ( Please help! )

[gordon stelter]

Ladies and Gentlemen of the List,
     I maintain a Yamaha U3 for a church here, which
is only one year old, yet has developed "bobbling"
hammers on about 25 notes. The immediate cause is that
the front edge of the jacks are not all escaping from
under the butt buckskin on letoff, althouigh the
keydip is "at specs", and the letoff is much more
generous than "spec": varying from 5 to 10 mm!
    My first effort at correcting this problem will be
to meticulously regulate this piano to Yamaha factory
specs, although I believe that this will only make the
"bobbling" worse. I believe that this will occur, as
the strange, current "regulation" on this little used
instrument ( besides the aforementioned "letoff"
distances, the hammers are checking at an inch or more
from the strings ) seems to have been effected to
overcome some inherent design flaw ( or flaws ) which
does not allow the jacks to readily slip out from
under the hammer butts.
   The percieved design flaw to which I refer is a
very sharp edge on the plastic jacks' front edge, 
which seems to catch on the buckskin, causing the butt
to bounce upon it repeatedly rather than allowing the
jack to fully slip out.  This problem  may also be
exacerbated by the use of an overly "nappy" buckskin,
and an unusually sharp angle on the hammer butt
buckskin face, at the point where where the jack would
normally "trip out".
    It seems that a tiny bevel, were it filed on the
front edge of the jacks, would be efficacious in
remedying this "bobbling". I may also try sanding down
the butt buckskin and lubricatinmg with some microfine
Teflon.
     My first efforts, however ( after regulating the
action ) will be to reduce the hammerstroke, and
perhaps increase the keydip by 1 mm.
     If you please: Have any of you encountered a
similar problem on a piano of this model and, if so,
how did you approach its remedy?

     Your advice will be gratefully recieved,
     Sincerely,
     Gordon Stelter 

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