Greetings:  When confronted with upright pianos with pinblock
laminations opening up, I have installed through-bolts that are
probably similar to what John Tuttle describes in his posting.

My approach has always been to lower the string tension a _lot_
(coils loose on the pins) throughout the piano, and back off any nose
bolts that stick through the plate from the back posts.  Then I'll
tighten up _all_ the plate bolts, including the new through-bolts,
similar to torquing the cylinder head on a motor.  I pour my favourite
glue into the pinblock cracks first.

I don't have any idea what the torque figures would be.  I crank on a
10" socket wrench until the cracks close or my wrist hurts, whichever
comes first.  Before pulling the pitch back up, I re-set the nose-bolts
to just contact the plate (with _no_ tension on the strings).

Occasionally I have found the plate already cracked at the mid-tenor
gusset, adjacent to a nose-bolt.  My suspicion in those cases is that
the pinblock opened up first, and the plate couldn't withstand the
string tension by itself.  It is often evident that the whole case
structure has twisted, even if the plate hasn't yet cracked.  The
nose-bolts are there to keep the plate from flexing when under string
tension, but if the case and pinblock are twisting, the nose-bolts may
actually force the plate to flex - and crack.

The pinblock opening that John describes (approx. 3/32") does not sound
too serious.  If it were much wider, though, I think it would be very
risky to pull a delaminating pinblock back together without lowering
tension and backing off those nose-bolts first, or the strange sound
that we hope not to hear could well be the plate cracking.

Cheers

Doug Rhodes, RPT