How to Fix a Sticking Jack

How to Fix a Sticking Jack

Sep 22, 2023

Fixing a Sticking Jack (Piano Tuning and Repair)

Welcome to our Series on Piano Tuning and Repair.

One of the most common causes of a sticking piano key is a jack that won't return. There are a couple of things that can cause this and we show you in this demonstration video how to diagnose and correct this problem.

If you want to see more of our Piano Tuning and Repair Series, click here to access the entire playlist.

Video Transcript:


Welcome to another video here by Howard Piano Industries. My name is Steve Howard and I am going to be showing you today how to fix a sticking jack, which is going to cause a sticking key. One of the main causes and probably one of the most common things that I come across that cause a sticking key, is a jack that doesn't return correctly. We are going to show you how to diagnose that as well as how to fix the problem so that your key works right. Here we have a note; we are looking at F#5 here. To identify the jack, it's this piece right here. I will show you a close up of a whippen with a jack out of the action here in a moment. That is the piece right there. What happens sometimes is when you push the key down, as you can see, the top of this jack comes forward as the note is played. What will happen is sometimes that jack won't reset underneath the hammer butt which is this piece right here. Sometimes it will go down and you will let the key go. I'm not letting the key go completely just so I can simulate what happens. But if you let the key go and the jack doesn't return completely back underneath that hammer butt, the note won't be able to continue to play. So you will be hitting it because the jack won't be completely under the butt, it won't push the hammer back up to play. So that causes what some would most consider a sticking key.

Checking for Lost Motion

Now the first thing you want to do is check to make sure that you have got a little bit of lost motion. Which means you have just a little space between the top of that jack and the hammer butt when the note is at rest. So you should be able to wiggle it: I've got this a little too close, but if you wiggle or if you pull back on your hammer rest rail just a little bit you should see that hammer move just a slight amount. Just a little movement of that hammer rest rail, if it comes back just a little bit that means there was room for that hammer butt to move before it reached the top of that jack. So that is the first thing you want to check. If there is no lost motion, or if the jack is too high you will have to adjust the capstan under here. I will be showing another video on how to adjust that.

Checking the Jack

But the main purpose of our video is to check the jack. Because this is a real common problem. If it is the jack, the other thing you want to check first is that the key is returning all of the way. Because if the key is not coming all of the way back up, or all of the way back down in the back then that is going to cause that problem too.

Whippen Closeup

But if we look here at a whippen with a jack, commonly, the problem is that your jack spring is not strong enough. We do show on another video how to replace those. Probably more commonly is that the pinning in this jack is to tight. Here is what's called a center pin that goes through this hole, that goes through this piece is the flange which is lined with felt and it goes through the jack. Then on the other side there is the other side of the flange with felt again. Okay so what you want to check to see is that if that pin is too tight in that hole, because what happens is that felt can swell and then this won't move freely enough. Which will make it so it doesn't have quite enough to return back underneath the hammer butt. So what you want to do to check that is you can disengage the spring and then check to see unless your not used to how much pressure there is supposed to be then it's hard to tell by hand. But if you move it like that then you can kind of tell if it's too tight. If it doesn't move very easily then it is going to be too tight.

Checking the Tightness (Gram Tension Gauge)

The more accurate way to check it is with a gram gauge. Which we sell in our store as well. So you can set that up and turn the jack kind of sideways like this so you don't have undue pressure from gravity. But then you can check your gram gauge. It should be if it's more than 6 or 7 grams that means it is too tight. Okay if we check this it's about between 3 and 4. It takes about 3 or 4 grams of pressure on the toe of the jack to move that jack. So that's pretty good. If it's too loose then the part is going to wobble and we don't want that either. But we want it too move freely. Now the pinning if you check the pressure on that and it's okay then it's going to be the jack spring.

Adjusting Jack Spring

To adjust this jack spring; what you can do is just pull up on it a little bit. You can even replace the jack spring, which is really the best option. If you want a quick fix you can just pull up on the spring to stretch it out so it's got a little more tension to it. There is a possibility that the spring will break by doing that if it's an old weak spring. But sometimes you can get that to work, if you don't have a replacement spring to get your piano working. But if this pinning is too tight and in most cases, really in the majority of the cases that is going to be the cause right there. If that pinning is too tight then your going to have to either lubricate it, which "Protek CLP" is the best option. If you're outside of the United States, it's a little bit difficult to acquire Protek CLP. We can't ship Protek products outside of the country because of the flammability factor. But that is the first thing you can try, and often times that will work to some degree. If it is too tight or you don't have access to Protek CLP you're going to have to re-pin the flange. We have another video which I will put a link up on in front of you to go to that video so that you can see how to re-pin that so that it is the right tightness. And we use our flange bushing broach kit, and of course, you would have to have center pins to re-pin that to the correct size. As well as a micrometer to know which center size pin you've got so you know what size you need to go to. So watch that video to show you how to fix that. But that's really the way that you can do to diagnose where exactly the problem is and what you can do to fix it.