Stack Reassembly + Head Shelf Installation + Regulation

Once the stack has been thoroughly tested and you are satisfied, it’s time to install the top shelf and the other peripherals as well.

The items that live on the top shelf include the spoolbox (which is commonly integrated with the shelf), the shifter (tracking) device, the air motor, and sometimes some other small valve boxes which serve as signal boosters (as is the case with mine).

The “head” consists of a shelf (horizontal piece in line with the yellow arrow above word “transmission”) and the various components attached thereupon

Assuming that your shifter and other valve boxes have been tested, and that your motor has been tested and regulated already, these things can be mounted on the shelf.
If you haven’t already done this, you can check out my earlier post on the shifter here, and my post about the air motor here

This is also a good time to tidy up any outstanding cosmetic issues, should there be any. I am thinking specifically of hardware and switches around the spool box area, as once the shelf is fully loaded these are harder to get at. I noticed that I had neglected to replace an old cloth washer on the spring loaded idler chuck for the music roll, so I went ahead and disassembled that completely and gave it a bit of spit and polish. I did not replate any of my hardware, but for the round and oval head screw heads, I did clean and polish them, to match the transmission which had received the same treatment. It was a more uniform look!

final polish and replacement of cloth washer in the roll idler chuck

We’ll look at the transmission in more detail shortly, but for now, reinstall it in its home, make sure everything is lubricated and free, in terms of the bearings and so forth. Different rebuilders use different products, including motor oil, sewing machine oil, 3-in-1 oil. I chose Mystery Marvel Oil. Whatever you use, only put it where you need it, and remember: “less is more”! Paradoxically, too much lubricant can spread to the upper brake drum; making the drum sticky over time and causing excess drag on the music roll!

Regulating the position of the take up spool and the clutch, as well as other transmission adjustments

Now, the spool box itself has to be regulated too, oh yes. First we align the take up spool to the tracker bar, so that it is centered in position (use the shifter/tracker holes as a reference). On my piano there is a lock nut on the right side of the gear shaft, in the transmission, to fix the location. With that done, now we set up the music roll idler (left) and clutch (right) shafts.
What is required here is that when a music roll is placed, and the paper drawn down and wound onto the take up spool, three things need to be in alignment:

  • The shifter (tracking) device, in neutral (center) position
  • The clutch (reroll) shaft centered on the tracking cam
  • The paper roll centered above the tracker bar, just as the take up spool is centered below


I have noticed that although the width of the paper on most piano rolls is 11 1/4″, there is variation in the thickness of the spool ends, which changes the precise location of where the roll sits over the tracker bar. This in turn will change the position to which the shifter defaults, when the piano begins to play. There is a bit of fiddling involved to achieve a happy medium between rolls of different brands.

Also note that all bearing points of the shifter linkage must be free, to respond smartly to the slightest signal of misalignment from the designated tracker bar holes. This is important!

Brakes: most transmissions have two brakes; one brake for play mode (which bears on the upper clutch/reroll shaft), and another for reroll mode (which bears on the lower gear/drive shaft).
Current convention dictates that the play brake should be regulated so that it presses just lightly enough to keep the paper from flying around loosely.
Most contemporary rebuilders are of the position that the reroll brake should be disengaged completely, so that older or original rolls have less of a tendency to rip or break when being rewound at high speed. Use your own judgement!

Cumulative testing, round 4

With the partial stack back on the bench, let’s review where we are, and confirm where we should be. At this point, the pneumatics were all tested on their decks, so we know they should be tight. The secondary valve chest has also already been tested, so that we know the chest is tight both when the valves are on, and when they are off.

While regulating the stack to the piano, the activation of notes may have shown any weaknesses in the secondary valves or pneumatics. If yes, fix them first. In other words, it is a good idea to continue the idea of “cumulative” testing by ensuring that the secondary chest and decks work well in concert, together, with no leaks heard either when the valves are on, or off.

Now let’s add the primary chest into the mix (assuming you have a double valve style stack), and run the tests again. The primary chest has the bleeds inside, so if there was an issue with sluggishness of returning secondary valves when testing repetition, this should be corrected and repetition should now be lightning fast. That is to say, the valves and pneumatics need to repeat as it is humanly possible, and then some; 10 reps per second is a good starting point. Any other problems relating to the interaction of the primary and secondary chest should manifest by now. For example, I discovered at this stage that two of my valves were weak (one was completely stopped, in fact), by troubleshooting the source of the problem I discovered that I had put too much sealant in two channels of the L board, so I had to rectify that problem before continuing.

With the suction attached, actuate each note in turn again, watching for rapidity and evenness of response. Listen for any leaks, and get visual confirmation if possible by calibrating suction loss with a vacuum gauge.

If the three main elements of the assembled stack (primaries, secondaries and decks) are performing well together: congratulations! It’s time to proceed to the last stages of the rebuilding.