1972 XS2 tachometer repair

Mailman

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I fixed this a few weeks ago and never wrote it up, so I thought I’d do it now. My tachometer used to be very smooth, then it started wavering a bit, then really jumping, then finally it stuck and wouldn’t return to zero.
This was a slow progression over several months time.

Time to fix it then. Honestly I hate to have to do this.
The process is hard on the tach. This was meant to be a sealed unit, it wasn’t built to be opened, you have to pry and bend and stretch it open. Metal distorts and stretches and fatigues, it never looks or fits quite like it did originally.
1C97FECD-94FC-4AC8-854A-441510CAC93C.jpeg


I don’t know.....you think this looks like a problem? My needle hanging up, the needle is not touching the dial face, the problem is internal.
2B020B0E-93B6-4F09-8D03-6A258D0B5BA3.jpeg


I put a reference mark with a marker, unsure if orientation would be an issue later.
89E44BE8-AD12-485C-8FD3-E95A8975E951.jpeg


Also, I can’t stress enough how important it is to take reference photos for later when you go to reassemble these parts, for me anyways , I use them constantly.

Here’s the first indication of the problem I’m dealing with, see all of the brass filings?
9240F28B-07AE-4B04-BD0E-8006F8B8DF5F.jpeg
8E9D6534-DE8A-450D-8050-7C420418A3CC.jpeg


The upper needle assembly has somehow dropped down and is making contact with the brass bushing that it spins in. Contact right here,
D29E9292-5593-42F7-B043-8BB562DF5885.jpeg


In this image , I have turned it upside down so you can see how much play is in there, you can see how that gap opened up.
178361AA-6689-4ECE-92CF-E1FD3E28D47F.jpeg


Here is a super short video showing how that bushing has wallowed out.


To take the assembly apart you must take a sharp chisel or a screwdriver and carefully drive these four staked edges back.

7A0E69C9-1A63-4A2B-91E0-0047DD3E10CC.jpeg


Then you can carefully pry the two halves apart.
D671D8ED-D8A6-4583-A5C7-62642EC0017B.jpeg


In the photo below, you can kinda get an idea how this thing works. The cable spins that cup in the lower part of the housing. Inside that cup is a strong magnet , the magnet has space all the way around, it does not touch the cup. The upper assembly , that turns the needle also has a cup, that drops down into that space between the magnet and the outer steel cup. The upper assembly and the lower assembly do not touch each other. And here is the part I don’t understand, the cup in the upper assembly is aluminum, how is that driven by magnetism?
BD4B182B-6FA2-4CF9-9D9F-D8E2CBA2709E.jpeg


When I first pulled it apart, I could see that there was gummy, oily residue and dirt on all the surfaces,

1D9AE51A-BC9B-4758-8D00-AABD56069348.jpeg


Here you can see , at the center, the brass staked surface that was rubbing on that bushing and creating the brass filings.
F19B2564-6E08-47B9-A549-B4B878D0B4CC.jpeg


And here I’ve removed for cleaning, the culprit, this super tiny brass bushing has worn out and allowed the whole upper assembly to drop down until it made contact.
756FE261-5611-404A-8AFB-818B41BA5218.jpeg


What I believe happened was just a cascade of events, over time any grease that had been in there has dried out, add a little dust and suddenly it started grinding open, that small hole that the shaft spins in.
The whole assembly then started wobbling and then things quickly accelerated.

At first, I was thinking that maybe if I cleaned everything up really well and greased the contact points, that I could get a few more years outa this. I did exactly that. Here I made a little video of me testing the reassembled parts. Nothing has been done except clean and grease and put it back together.


In the end, I rejected this idea, because the root problem was not addressed. It would work , only as long as the grease held up.

At this point my repair stalled out.
My tach sat on my bench for a couple of weeks, while I tried to figure out how to repair this. 2M has the most experience with these old tachs, So I went to see The Oracle !

Steve recommended replacing that little brass bushing, but how? He said it could be done by a hobby machinist, he even offered to do it. ( He really is the best ! ). But I had been reading a lot and found someone here ( I’m sorry I forgot who ) who had drilled out that little bushing and tapped the hole and replaced it with a brass screw which he then worked into a bushing. So I had considered doing that.

At this point GLJ ( Greg, kindly offered to supply me with a used tach, but I know he has the bones to maybe make another XS2 someday, so I didn’t accept his kind offer )
Jim also said he had a tach from an XS1 that he couldn’t use, so I did accept that one from him.
So....
8EEB7678-E879-4E33-9BCC-95AA03A4E87C.png
Thank you Jim!

Jim actually opened his up and sent me the internal parts. Here is a little photo essay of the differences between the XS1 and the XS2 internal drive. Some physical differences, but the drive component is the same.
0FDE864B-5ADE-4C21-9B59-4B2D995BB07B.jpeg 31746AEE-D9DC-4D5D-AC4A-AA8A3E1CA2E5.jpeg 2CFDEE17-B965-4FF1-AE1C-1CBDD8C38887.jpeg 63F87919-C6F1-47A5-91DF-AED6D8C72B72.jpeg

Here is the money shot. Notice how much higher his tach needle shaft sits above the top plate. That’s because his bushing isn’t worn out. Yay!
231F7228-0CF9-42EF-9017-673C2FAB8FF6.jpeg


I ran a little test with the drill to confirm that it did indeed work, then I tore it apart for cleaning. And I discovered some wear on the spinning cup. So all I wound up using was the little arm that has the brass bushing in it. Everything has been cleaned, lubed and reassembled and here is my final bench test.


Stick a fork in this one because it’s done! It’s been back on my bike and ridden a few times and all is well.
That’ll do.....that’ll do.
BA43A490-42E7-49D4-BA4F-21A30C592477.gif


Later, Bob
 

TwoManyXS1Bs

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geedubya

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I fixed this a few weeks ago and never wrote it up, so I thought I’d do it now. My tachometer used to be very smooth, then it started wavering a bit, then really jumping, then finally it stuck and wouldn’t return to zero.
This was a slow progression over several months time.

Time to fix it then. Honestly I hate to have to do this.
The process is hard on the tach. This was meant to be a sealed unit, it wasn’t built to be opened, you have to pry and bend and stretch it open. Metal distorts and stretches and fatigues, it never looks or fits quite like it did originally.
View attachment 151215

I don’t know.....you think this looks like a problem? My needle hanging up, the needle is not touching the dial face, the problem is internal.
View attachment 151216

I put a reference mark with a marker, unsure if orientation would be an issue later.
View attachment 151217

Also, I can’t stress enough how important it is to take reference photos for later when you go to reassemble these parts, for me anyways , I use them constantly.

Here’s the first indication of the problem I’m dealing with, see all of the brass filings?
View attachment 151218 View attachment 151219

The upper needle assembly has somehow dropped down and is making contact with the brass bushing that it spins in. Contact right here,
View attachment 151220

In this image , I have turned it upside down so you can see how much play is in there, you can see how that gap opened up.
View attachment 151221

Here is a super short video showing how that bushing has wallowed out.


To take the assembly apart you must take a sharp chisel or a screwdriver and carefully drive these four staked edges back.

View attachment 151222

Then you can carefully pry the two halves apart.
View attachment 151227

In the photo below, you can kinda get an idea how this thing works. The cable spins that cup in the lower part of the housing. Inside that cup is a strong magnet , the magnet has space all the way around, it does not touch the cup. The upper assembly , that turns the needle also has a cup, that drops down into that space between the magnet and the outer steel cup. The upper assembly and the lower assembly do not touch each other. And here is the part I don’t understand, the cup in the upper assembly is aluminum, how is that driven by magnetism?
View attachment 151228

When I first pulled it apart, I could see that there was gummy, oily residue and dirt on all the surfaces,

View attachment 151229

Here you can see , at the center, the brass staked surface that was rubbing on that bushing and creating the brass filings.
View attachment 151230

And here I’ve removed for cleaning, the culprit, this super tiny brass bushing has worn out and allowed the whole upper assembly to drop down until it made contact.
View attachment 151231

What I believe happened was just a cascade of events, over time any grease that had been in there has dried out, add a little dust and suddenly it started grinding open, that small hole that the shaft spins in.
The whole assembly then started wobbling and then things quickly accelerated.

At first, I was thinking that maybe if I cleaned everything up really well and greased the contact points, that I could get a few more years outa this. I did exactly that. Here I made a little video of me testing the reassembled parts. Nothing has been done except clean and grease and put it back together.


In the end, I rejected this idea, because the root problem was not addressed. It would work , only as long as the grease held up.

At this point my repair stalled out.
My tach sat on my bench for a couple of weeks, while I tried to figure out how to repair this. 2M has the most experience with these old tachs, So I went to see The Oracle !

Steve recommended replacing that little brass bushing, but how? He said it could be done by a hobby machinist, he even offered to do it. ( He really is the best ! ). But I had been reading a lot and found someone here ( I’m sorry I forgot who ) who had drilled out that little bushing and tapped the hole and replaced it with a brass screw which he then worked into a bushing. So I had considered doing that.

At this point GLJ ( Greg, kindly offered to supply me with a used tach, but I know he has the bones to maybe make another XS2 someday, so I didn’t accept his kind offer )
Jim also said he had a tach from an XS1 that he couldn’t use, so I did accept that one from him.
So....
View attachment 151234
Thank you Jim!

Jim actually opened his up and sent me the internal parts. Here is a little photo essay of the differences between the XS1 and the XS2 internal drive. Some physical differences, but the drive component is the same.
View attachment 151235 View attachment 151236 View attachment 151237 View attachment 151238

Here is the money shot. Notice how much higher his tach needle shaft sits above the top plate. That’s because his bushing isn’t worn out. Yay!
View attachment 151239

I ran a little test with the drill to confirm that it did indeed work, then I tore it apart for cleaning. And I discovered some wear on the spinning cup. So all I wound up using was the little arm that has the brass bushing in it. Everything has been cleaned, lubed and reassembled and here is my final bench test.


Stick a fork in this one because it’s done! It’s been back on my bike and ridden a few times and all is well.
That’ll do.....that’ll do.
View attachment 151240

Later, Bob


B-O-B,

I used to repair these sort of instruments and I am thinking of going back into business..............any chance you would like to immigrate to The Land Down Under??

Mate, lots of good beer, good looking girls, plenty of open roads to ride, oh and of course in my area The Great Barrier Reef.

GeeDub
 

peanut

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thats an excellent article/guide Bob thank you for recording that .:)
Its doubtless going to be a valuable resource for others that follow in your footsteps and give confidence to those contemplating the job themselves
 

Mailman

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Thanks Geedubya and Peanut! It’s funny but I remember reading a few years ago 2Ms excellent article about opening up his old tach and repairing it. At the time I thought, oh man, I would never try something like that. The last couple of years have broadened my horizon. I find myself doing a lot of things that I wouldn’t have attempted before. Such is the value of this forum.

And Geedubya, careful about throwing those invitations around. Someday some old gray haired vagabond may come knocking at your door! :cool:
 

fredintoon

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I fixed this a few weeks ago and never wrote it up, so I thought I’d do it now. My tachometer used to be very smooth, then it started wavering a bit, then really jumping, then finally it stuck and wouldn’t return to zero.
This was a slow progression over several months time. - - - Time to fix it then. Honestly I hate to have to do this.
The process is hard on the tach. This was meant to be a sealed unit, it wasn’t built to be opened, you have to pry and bend and stretch it open. Metal distorts and stretches and fatigues, it never looks or fits quite like it did originally. - - - And here is the part I don’t understand, the cup in the upper assembly is aluminum, how is that driven by magnetism? - - -
Later, Bob

Hi Bob,
yeah, the hard part is removing & replacing the instrument's front glass. In my case, just to put the faceplate retaining screws back in.
The first instrument took hours of careful prying to R&R the bezel. The second bezel was cut off in two C-pieces and epoxied back on.
Which works a lot quicker but it only works once.
And how does an aluminum drum get turned by a magnet? The Wizards will mutter "reluctance" which is a posh word for "magic".
 

Mailman

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Ok...I’ve been trying to read about this. I still haven’t found anything specifically about how magnetic fields can move a non ferrous object. Would I be way off in comparing a fast moving magnetic field sort of dragging or pushing a non ferrous object? Sort of the way we can’t see wind, but we can feel it push against us?
 

Jim

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Ok...I’ve been trying to read about this. I still haven’t found anything specifically about how magnetic fields can move a non ferrous object. Would I be way off in comparing a fast moving magnetic field sort of dragging or pushing a non ferrous object? Sort of the way we can’t see wind, but we can feel it push against us?
Copper is also non-ferrous. Watch this crazy stuff....

 

geedubya

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Thanks Geedubya and Peanut! It’s funny but I remember reading a few years ago 2Ms excellent article about opening up his old tach and repairing it. At the time I thought, oh man, I would never try something like that. The last couple of years have broadened my horizon. I find myself doing a lot of things that I wouldn’t have attempted before. Such is the value of this forum.

And Geedubya, careful about throwing those invitations around. Someday some old gray haired vagabond may come knocking at your door! :cool:


B-O-B,

My casa, your casa.........my home is always open to grey haired XS650 vagabonds............as long as they bring beverages.

GD
 
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