Method: Rebushing

One of the final tasks on the checklist before motor reassembly is rebushing. There are many, many bushings of different descriptions and purposes in a player piano (or a regular piano), but they are mostly variations on a theme.

A bushing is a piece of material (usually sturdy cloth) which creates a sort of “buffer zone” between a moving part and a stationary part. For example, anywhere there is a pin or rod that rotates, chances are good that there is a bushing around this part. A bushing must be the right size: too thick and it will induce unwanted friction, too thin and the moving part will not have sufficient support, causing inefficient mechanical motion and probably unpleasant noises as well.

For the present post, we are referring specifically to the bushings in the motor. You will want to redo all of these bushings, especially the ones that come into contact with the crankshaft (which is most of them). This motor has got to run a long time, so let’s freshen up those bushings and keep it tight!

Let’s start with connector arms and valve flanges. Remove the old cloth. Before we get too far ahead, you might as well clean out the bushing holes of old residue with a properly size drill bit. The fit should be snug, but don’t ream the hole any larger.

Now measure the old cloth. You will need to match the dimensions of the original bushing, the key word being original. There are two dimensions to watch for here: thickness and width.
The length of the bushing will not have changed, so when you cut a strip of cloth, the width of the cloth must match the length of the old piece. If ever the bushings are damaged or missing, you can approximate by remembering some geometry: the circumference of a circle is π x diameter. In other words, if you measure the span of the hole, multiply by 3 (and a smidge), and cut your cloth strip to this width, it should be a pretty close fit!

The thickness is tricker; measure the thickness with calipers or similar gauge, and then realize we must account for wear. Depending on wear, we may need to add ten to twenty thousands (of an inch) to replicate original cloth.

Once you’ve got something you can work with, tear a strip (good quality cloth will tear cleanly and evenly, just as well as cutting) of the proper width, as long as you need.  For bushings that go in a hole (in a block of wood), cut a bit away to make a “tip” on the strip and pull it through the hole, almost the entire way through. If you look at the cloth sitting in the hole, the two sides should touch each other, but without having the cloth bunch up in the hole. If there is a gap, your cloth is too small. If it bunches: Too big!

Then put a reasonable amount of glue (you will figure this out on your own) on the cloth and pull it the rest of the way into the hole.  Assuming you’ve used hot hide glue, let it set up for a few minutes (while you do the next, and the next), then double back before the glue hardens completely and trim the excess cloth.

There is a trick to this, and it involves a sharp instrument like a new razor blade. Nothing screams “amateur!” like sloppy bushings cut with a dull blade. To avoid dislodging your new bushing with the blade, insert a stand in mandrel (like a wooden dowel) of proper size into the bushing hole. Hopefully it goes without saying that you don’t use your crankshaft as the cutting mandrel!

For bushings which can be put in place without the above method (e.g. open cavities), you should be able to cut to size before gluing in place, as is the case with the following slide valve arm flange bushings.

Old slide valve bushings
new bushings and cloth for the slide valves

And whadya know – John Tuttle has a video on this subject too! I’ll let him offer his perspective again – click here!

There are still more kinds of bushings, such as those for the side guides of the slide valves. These will be a snap, after having done the rotary ones. They are just strips of cloth!

Slide valve guides, with bushings

Once your various bushings have all been done, collect everything (back in the correct order), and get ready to put the motor back together. Almost there!

all arms and flanges back on pianola motor crank shaft

Leave a Reply

Your email address will not be published. Required fields are marked *