Shank seizing and bushing migration

6. RE: Shank seizing and bushing migration

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Registered Piano Technician

Andrew Lyford

Posted 02-07-2025 08:55

Not yet! I do now take care of a beautiful slightly used M&H BB. I had hammer flange bushings walking out on those parts. Surprised me.
Andrew J. Lyford, RPT
Lyford Piano Works
pianotechandy@gmail.com
276-732-6290

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10. RE: Shank seizing and bushing migration

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Registered Piano Technician

David Love

Posted 02-08-2025 01:05

I only repinned one or two where the bushing needed to be replaced in the initial go round. The pins looked fine.

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David Love RPT
www.davidlovepianos.com
davidlovepianos@comcast.net
415 407 8320
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11. RE: Shank seizing and bushing migration

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Registered Piano Technician

Don Mannino

Posted 02-08-2025 19:12

The cause is that the bushings themselves were installed with the cloth in an unstable state. This is exactly what was happening in the Young Change action parts in the early 1990s when I worked for them. I worked in the factory in Inchon, Korea for a 2 week testing session where we were able to identify the issue.

The cloth is initially wet-sized so that the friction is fine (frequently a little too low) when the parts are shipped. With use the cloth is being shaken and jiggled and twisted, and the wool fibers move around in the bushings and start to bind on the pin. In Korea I discovered this by using a number of different installation and sizing procedures. The procedure that factory used was leaving the cloth in this unstable state, and it is the same process that Abel was using a few years back.

The issue came up very quickly in pianos that had player systems and were installed in hotel lobbies and such - the regular use caused the parts to go tight in just a week or two of steady playing. In most pianists home it takes a while to start to go bad.

In Korea I tested this by drawing ink lines across the bushings, then putting the shanks in the testing machines and running them overnight. In the morning the shanks were all tight and squeaking noisily, and when I inspected the bushings in the stereo microscope we had on hand you could see that the ink lines on the wool fibers were gone. Looking closely, we could see black dots scrambled around in the bushings because the wool fibers had shifted all around.

Once the fibers have moved around like this then they can be broached and sized for new pins and assembled. They do not continue to bind. In our testing at Young Chang I also tried disassembling new parts (before they were played in and tested) that had been built using the questionable installation process. I fitted them with a larger sized broach, then installed new pins and put them in the test machines overnight. We had no tightening up at all in those parts. I was actually criticized because these parts would loosen up an average of 0.5g in friction from testing!

When inspecting the center pins that had gone tight in the test jigs (I believe we had 12 complete action stacks being tested every night, with a mixture of bushing cloths, glue, pin types, and fitting procedures being tested every night) we saw the dull marks where they contacted the bushings. The pins were literally being worn away by a combination of the tight bushings and the metal dust that built up from the tight fit. The wool fiber's surface scales were literally scraping metal powder from the pins. Wool is amazing stuff! That is what you see in some pins from heavily used actions that have gone tight in use.

If the bushings are coming out, that means the factory was trying to use a minimal amount of glue, and they weren't adhered well to the wood. Those do need to be rebushed of course.

I know some companies over the years have blamed excess glue as causing the tightening up in use. It does happen sometimes when too much glue has been used, or it was too thin and penetrated the bushing too much in assembly. This leaves a very clear white ring of glue on the pin which can be scraped off with your fingernail. I have broached and repinned quite a few of these sets of parts and also have had no difficulty with them afterwards - the damage is done, I think, during the wet sizing process, and after dry the glue has not caused more seizing up.

Regarding plated pins, we rigorously tested these and compared them with non plated pins. There was no difference at all in the performance or reliability. The reason plated pins are used is because they work more reliably in the factory machines that automatically assembles the parts. The surface is harder and they are less likely to catch and bind in the machinery. I have inspected hundreds (if not thousands!) of center pins over the years and have never seen plating come off and cause issue, except in very rare cases when dull cutting tools were used to cut the pins and cause the plating to crack slightly.

Schaff pins are not plated, and I use them for most of my repinning work. Some of these I have bought over the years have not been well polished, but it hasn't caused any trouble for me, and didn't cause any issues in my testing in Korea back in the early 90s. I've bought pins from Renner and other sources in the past, but haven't found any real benefit - although some suppliers over the years were more accurately sized! Recent pins I've bought from Schaff have also been sized correctly.

Finally, I want to say that I have experienced this exact issue in action parts from pretty much every major piano company! Action centers are extremely difficult to make well. I used to install Renner parts in my rebuilds during the 1980s and I quickly found I had to repin every set before letting the piano go out. I have worked on Steinway pianos with NY and Renner action parts that behaved this way. I have had it in some Kawai actions even - although with Kawai I have never seen it in grand shanks, as they have an incredibly good process for fitting and assembling the grand shank action centers. However, sometimes upright action centers will go tight. Same with some Yamaha upright jacks, hammer butts, and wippen flanges - sometimes, but not commonly. It has recently cropped up in some European piano makers, and I suspect these have been from the same shanks that people are discussing here - pianos built from 5 to 10 years ago roughly, maybe even older. I've also seen it in Tokiwa action parts from Japan, and from action parts from some Chinese makers. Samick pianos have had it happen a lot, as others on this list have mentioned. Over the years I've been working on pianos it literally has happened to every action maker!

So far, no issues from the Mason & Hamlin hard bushings, they seem extremely reliable.

I bought new Abel shanks for my own piano at home 2 years ago, and with regular playing I haven't had any tightening up of the hammer shanks yet. I did not repin these, so they should be a good test.

For those who might not know, I worked 5 years for Young Chang in the early 90s, and I then worked 27 years for Kawai. I am now retired from corporate work and am back to doing private piano work - and have just recently done a few repinning jobs of this type!

Don Mannino RPT

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12. RE: Shank seizing and bushing migration

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Registered Piano Technician

Peter Grey

Posted 02-08-2025 19:48

Don,

Thanks for the excellent information here. One thing though I'm having trouble with is the idea of the cloth being unstable vs stable. I'm not sure of what I'm missing, so could you elaborate a little on this please?

Peter Grey Piano Doctor

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Peter Grey
Stratham NH
(603) 686-2395
pianodoctor57@gmail.com
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Original Message

Original Message:
Sent: 02-08-2025 19:11
From: Don Mannino
Subject: Shank seizing and bushing migration