Located on the head, the motor is a key component of the player action. The motor is what transduces rotational kinetic energy from air pressure. In other words, you pump pedals with your feet, which creates air pressure differentials in the system (which the system is designed around).
Then, these differentials in pressure cause the motor valves to repeatedly open and close, which in turn causes the crank arms to turn the crankshaft in a smooth and predictable way. The crankshaft engages the transmission (via ladder chain), which is connected to the spoolbox flanges. The roll starts to turn, and the magic happens!
In a visual sense, the motor is also the centrepiece of the upper action, due to the dynamic motion which draws the eye, from the music roll and back again.
As I will do with each component, after the parts restoration is complete, a thorough test and troubleshoot will be performed, to verify the functionality of the piece.
Let’s take a step back for a moment. Due to its position on top of the action, the motor is one of the most accessible components, and was among the first to be removed and disassembled. In fact, sometimes the motor must be removed or at least shifted during routine piano maintenance such as tuning or broken string replacement.
This particular model is a fairly standard 5-pt motor, quite reminiscent of Autopiano style. It consists of a main trunk, 5 slide valves and 5 pneumatic bellows. The trunk is essentially a wooden box with a precise design of holes drilled to create channels and ports. On the face of the trunk are the slide valves, which control whether a given pneumatic is opening or closing at a given moment. On the back, the pneumatics are mounted. Both the slide valves and the pneumatics are connected by flanges to the crankshaft, mounted above the trunk. As the bellows open and close in sequence, each bellows flange (connected via a crank arm to a lobe on the shaft, offset 72 degrees from its neighbor) pushes the crank on the power stoke, so that the crankshaft is always following a smooth rotation (assuming the motor is properly regulated – more on that later). In this manner the music roll renders its performance in a seamless way.
And now the dismantle. As with the spoolbox, the key here is just to start by taking out every visible screw, one by one, while documenting extensively your actions! We don’t want to get off on the wrong foot here!
It should all come apart without too much effort. If there is one component in this action which is meant to be serviced, it is the motor. Some photographic highlights of teardown:
After unscrewing and carefully separating everything the only thing remaining is the bellows on the trunk. Record the span (they should all be the same), and then take them apart. Slit the cloth lengthwise along the sides and open end. Rip the hinge apart and separate the boards (how violent!). You will have to knock or steam off the stationary boards. Whether you are tackling the motor or the stack, the same principles prevail. Once again, John Tuttle to the rescue with a video on this topic:
Once the surgery is over, it’s time to clean and sand all the boards (keeping them all equal dimensions and perfectly square), and the trunk back. Since we are just talking about 10 boards here (5 pairs of bellows), it’s up to you whether you prefer the hand sanding option or power tools. I don’t have a belt/disc power combo at present, so that’s an easy one for me. And it doesn’t take a lot longer. But when it will come time for all the stack pneumatics, that will be a different story. In the meantime, to do boards these by hand, get a nice flat surface (plate glass), slap some 180 grit paper down, put a jig (a simple 2×4 cutoff will work, if square), and sand that sucker straight and true. Repeat.
As for power tools, here’s an observation: the wonderful thing about them is that results happen extremely quickly, compared to hand work. Know what else happens extremely quickly? Mistakes! As Peter Parker once said, with great power comes great responsibility. You must know and respect your machine, or it will take advantage of you, damaging your work, and even your body if you are not careful — you have been warned!
See directions for this procedure (similar, but not identical) on the front, in a follow up post. No power tools needed there.
Then, you will finally be done the dismantle! Come back next time!