Ref. http://mmd.foxtail.com/Pictures/herrPiston.html

To Randolph Herr and the MMD Group,  This piston motor is from the
early Type I Gulbransen player.  The roll motor, transmission and
spoolbox are all suspended by metal brackets so close to the top of the
piano that they're almost oozing out of the lid.  The trackerbar tubing
then dangles down to the stack, requiring quite a bit more tubing than
the average 88-noter.

The stack is remarkably similar to the late Type III stack with
screw-on unit valve/pneumatics but having four tiers instead of three.
The pneumatics are much wider but with an extremely small span, not
more than 3/8" I think.  The finger is part of the bottom leaf of the
pneumatic board requiring the notching of the cloth before covering.
The finger then engages with the abstract of the piano action where
an eye-screw and felted button can be regulated to the pneumatic.  The
valve was nearly identical to the type II's and III's.

The type II is the glued together stack most often encountered,
most likely to ignite heated arguments between professional rebuilders
or become heating fuel for your Franklin stove.  The type I is
comparatively easy to rebuild provided you don't destroy the remarkable
little motor in the process and you're really good at cutting cloth and
recovering small pneumatic without fusing them together.  The type III
was basically the type II sawed up into individual unit pneumatics just
like the type I only streamlined from four tiers to three.
(Apparently, Gulbransen did the same thing the Microsoft "improvement"
method as applied to the player piano, like make Windows XP function
the way Windows 95 did.)

The type I motor (as pictured in the MMD Archives) is mostly made of
brass that was then plated.  Unless the pistons are leaking there is
no need to force open the cylinder chambers if you can avoid it.  But
here's what is inside:  about a quarter sized (or so) disc of either
pot-metal or lead.  Lead, you hope.  A rod through the center of the
disc is exposed at the top of its travel and the other end connected to
the crankshaft and to the slide/distributor valves via a cotter pin.

Getting at these pistons isn't easy, the chambers are probably soldered
like the distributor tubes coming out of them are.  The vertical rods
are heavily bushed on the top and bottom and probably loaded with
grease.  Eliminate the possibility of a leak here before attempting to
bust open the chamber;  if you can it will save you the trouble of
having to re-solder the distributor tubes or whatever else broke loose
or got bent only to find out everything was probably OK to begin with.

But the real fun is the distributor valves themselves.  Since they are
partially exposed (linkage/venting ports) and probably over-oiled,
they will likely have developed enough grooves in them to leak or not
work at all.  Or, if they are pot metal, it's possible they've cracked
and are swelled stuck inside the chamber.  Ideally you should be able
to unscrew the threaded linkage pin from the valve and it will fall out
of the distributor chamber.  At this point, you can stuff enough scrap
leather inside the distributor chamber to test the main pistons.

But if the distributor valves are stuck be careful of how you go about
plunging out the middle one-- it only comes out of one side, I've
forgotten which.  The valves are notched to admit atmosphere or vacuum
to the pistons via the distributor tubes and must not be mixed up.
There is no adjustable way to time this motor other than changing the
porting of the notches so do be careful of this.  Also, the linkage
from valve to crankshaft must be reassembled exactly as it was, screw
it in too far and you could cause it to expand enough to get stuck
again inside the distributor tube or not have enough length to attach
it back to the main crank.  Or vice versa.  The main thing is to
reassemble everything exactly as it was.

The three main pistons can be lubricated with a few drops of a medium
weight oil applied to the rods as they emerge from the top bushing.
The distributor valves and interior of the distributor tube should be
given a light, even smear of Vaseline before reassembly.  Then a very
few drops of oil can be applied if needed.

Be sure the bushings on the main crankshaft are firm enough to
eliminate any play but not so tight they bind unevenly on any part of
the revolution.  The same applies to the rest of the moving parts and
be sure to inspect all of the tubes for cracks in the soldered joints
to eliminate any possible leaks there as well.  Unless the main
discs/pistons are spilling vacuum from one chamber to the other or they
are binding or travelling unevenly you can save yourself a migraine by
not disassembling the main piston chamber!

These little motors were probably quite costly to produce which would
explain why Gulbransen decided in favor of the wooden bellowed roll
motor.  Strangely enough, the piston motor emits a similar "chuffing"
sound that the rotary valves do in the more common type II and III's
except somewhat louder.  The type I motor is a little "choppy" at low
speeds and although very fast during rewind it does take a few seconds
for it to build up momentum to full speed.  Perhaps a fourth or fifth
piston chamber and valve would've eliminated these shortcomings but
considering what the bottom line in production cost (let alone the R&D)
would have been it's easy to see why this funky little motor was
retired in favor of the cheaper wood and cloth thumper.

The one working motor of only two I've ever seen is still functioning
in the Segerstrom piano it was installed in.  The other one was in a
early Steger upright with only the spoolbox and motor remaining;  I
desperately used it to rebuild the other one after nearly destroying the
first by dismantling it to death out of curiosity.  Hope this helps in
avoiding the frustrations I had but believe me, anyone who saw it work
didn't give a damn about how the rest of the piano sounded.  The motor
was just that cool...

Respectfully submitted from the useless information department of:
Eric J. Shoemaker
Bellevue, Washington