After reading the several posts on this subject, I would like to add my
two cents worth.  I always strive to restore to the original and having
all six bellows the same size is important.  My 1917 Aeolian air motor
had motor cloth stopping about 1/4 inch from the hinge and then they
used larger pieces of leather to cover this end area so the surface was
even on the ends of the bellow structures.

So, Michael, if your motor is similar, I would cut six pieces of motor
cloth, 3-1/2 inches wide, 9-3/4 inches long and six pieces of leather
about twice as thin as pouch leather measuring 2 inches by 2-3/4 inches
for the ends.

Rather than speculate or estimate on the amount to shim an end while
doing the other end, I first measure each of the unrestored double
units after they are disassembled into three pieces.  The last motor
that I restored, I firmly held one end fully closed and measured the
fully opened end and then reversed and measured the width of the other
fully open end.

Each fully opened end measured 2-5/8 inches so when recovering the
first three opposite ends, I used the necessary washers as shims
secured in place with a piece of masking tape and the bellows held firm
with a couple of strong rubber bands to create the 2-5/8 inch opening
on the other ends.  After trimming and putting the proper crease and
folds in the completed ends, I did the other ends setting up the 2-5/8
inch opening, again using the washer shims and rubber band procedure.
(You use 3-1/2 inch width pieces of motor cloth rather than 2-5/8
inches and the over-hang is used to fully cover the sides of the
bellows wood.)

And Michael, I would recommend using PVC-E or PPCo 320 glue for gluing
on the bellows cloth and leather as it is effective and much easier to
use than hot glue for a beginner.  The Reblitz book has some good tips
on restoring the air motor too.  You will just have to wade in and you
will learn a lot just by doing the work.  You will find that a lot of
restoration work will rely on your ingenuity and for the most part,
you will not have or need books or diagrams to directly tell you how
to do each job.  (Feel free to drop me an e-mail though if I can assist
further.)

Larry Schuette
Raymond, Nebraska