Bobbling hammers of Yamaha Uprights

[James Ellis]

I have been reading your various posts on the subject of bobbling hammers
on Yamaha uprights.  I tune a fairly new Yamaha P22 that has just started
doing it on a few hammers, but by no means all of them.  I looked closely
to see why.  It is NOT regulation.  It is NOT damper spring strength.  It
is NOT that I don't follow through on the key stroke.  In fact, most of the
hammers don't bobble, no matter how I play.  On those that do, I have to
pound hard, or they will.  Those things I just mentioned: NONE OF THE ABOVE.

Here is what I found.  It's the shape of the butt and butt leather.  On
those that are bobbling, there is more of a lump at the very front of the
leather than on those that don't bobble.  I found two hammers, side by
side.  One always bobbled, unless I banged it hard.  The other never did.
I pressed both keys down firmly.  Both jacks moved back by the same
distance. One bumped the outward end of the butt leather, but the other did
not.  This is the only piano I tune regularly that has this problem, but it
does, and on a few notes, it has it bad.  Otherwise, it's a very nice piano.

Keep this in mind before you go bending things as a quick fix.  The quick
fix is a tiny bit more dip, or a tiny bit closer checking, or a very
slightly sooner let off, or a combination of all.  But that's not the real
fix.  The real fix would be to get that hump off the front end of the butt
learher.  Otherwise, the jack will have to fly way back, farther than it
should, to clear it.

That's what I found on this particular piano.

Jim Ellis