Tach Repair

First, I apologize for the crappy pics.  My real camera (an old-skool 35mm Canon that uses real film) has a dead battey in it, and I don't have (or want) a digital camera. However, Motorola puts something into their RAZR cellphones that they call a camera (it isn't much of one really), so I took all these pics with the cellphone.

We've all seen Roger Pariseau's page about how he fixed someone's tach, so I used his instructions as a reference when I started mine. (Nov 2008 - The above link to Pariseau's page is now dead. But I do have a copy of his page HERE ). However, he didn't take the tach movement itself apart, and the bezel he shows was cut by a dremel.  Also, in August, there was a posting on the CB_750 group at Yahoo by Jamie who fixed Jay's tach.  He had pried-up the bezel lip so I knew it was possible to do so.

First, get the tach off of the bike...

  1. Remove the bolts holding instrument cluster to tree.
  2. remove the screws holding tach into silver housing
  3. open headlight bucket and disconnect the 9 pin connector, pull wire bundle out of bucket
  4. disconnect the 4 wires on the underside of the cluster (to turn signal light and the backlights for speedo)(wires are color-coded, when you go to put them back together, just match the colors up)
  5. pull the wire through the housing (rubber seal/plug probably will come out too, that's OK)
  6. put the housing screws somewhere safe, or put them back into the barrel bolts like I did.

OK.  Now you should have this

pull the black rubber ring off and you can see the back-side of the silver bezel.  It's really smooth and properly crimped.  Won't be for long... ;)

Removing the bezel:

Pariseau shows a bezel that has been cut through with a dremel.  I dunno how he got it to go back on after he repaired the tach.  Following a post by Jamie, I decided to pry up the lip on the underside of the tach.  I used a flat blade screwdriver and patiently worked my way around the perimeter.   To get it started, you have to kind of force one corner of the screwdriver under the bezel - a gentle twisting motion will help the tip start lifting the metal.  Once you get it started, it's not so hard, but it is mind-numbingly repetitive.  So to keep from getting bored, think of all the nice things you'd like to say to the Honda engineers who decided to use such a wonderfully constructed tach on the Nighthawk.  If only they spoke engrish.

I made two passes around the bezel so as not to stress the metal too much by trying to lift it too high at once.  And even after two passes, I still had to go back and finesse parts of the bezel so it would lift off of the shell.  You'll see what I mean when you do it.

As you can see, this really scars up the plastic shell and the lip that's under the bezel.  I don't think it causes any significant structural damage to the shell though, and we can sand/scrape the ugly scars down a little when we put it back together.


At this point you have something that looks like this (minus the messy workbench):

See that black ring behind the glass?  Don't forget which way it goes in when you put it back together, or you'll cuss like a sailor if you put it in upside down and don't realize it until after you've crimped the bezel back on...


Removing the tach guts:

First, remove the screw that holds the wire clamp down.  Then you can move the cable out of the way.

I dunno if it makes any difference, but I removed the bigger screws first, then removed the smaller electrical screws. 

WARNING: keep your hand under the open face of the tach when you take the last screw out.  The guts will fall right out once you remove the last screw.

Here's the inside of the shell.

Nothing there that interests us, but that's what it looks like.

Here's the part we are after - the actual tachometer.

here's a bottom view showing the circuit board.

Nothing there really interests us much either.

As with Pariseau's writeup, here is my fuzzy picture version of the opening into the movement.

It is smaller than it seems.  That part of my finger that you see is only from the first nuckle to the tip - less than an inch. 

And yes, my tach had the same problem as all the rest - the inner solder joint on the outer-most spring (the one closest to the tach face) had come lose.

Now, here is the point at which I diverge from Pariseau's writeup.  I think he did his repair with the D'Arsonval movement still assembled, and claimed it was a huge pain in the ass to get a soldering iron down to the inner coils of the spring.  Same thing from Jamie.  However, I am insane, so I decided to take mine completely and totally apart.  After all, it's already broke and I'm already crazy, so what have I got to lose?

Pop off the plastic that holds the circuit board in place.  Not hard - just pry it up with a screwdriver.  There are no screws holding it together, just two plastic pressure pins that you see in the second pic.

Now you need to do some marking with a sharpie marker. (this pic is from 2 steps ahead - after removing the needle, but is the only one that shows the mark I made).  If you move the needle, you'll see the actuator arm moving inside of the movement (it's the part that has the coil on one side).  With the needle at 0 RPM (against the black stop pin), mark the rough location of where the center of the actuator arm is.  Also, make a mark on the metal horseshoe that shows where the right side of the actuator arm is (can't see that mark in this pic).  You'll need these marks when you go to put the tach back together - it'll get you close to 0 RPM (although, as we'll see, you probably won't hit 0 exactly the first time).  I eyeballed my marks when I made them - you might figure out a way to use a straight edge and make a more accurate mark.  If you do, let me know how and I'll update this step.


Now remove the needle.  This is sorta aggravating.  My needle is 14 years old, and the UV has made it a bit brittle, AND it fits really tightly to the shaft.  I snapped mine while removing it - broke it right past the black hub.  Best way to remove it - flat blade screwdriver under the hub, and pry it up, moving the screwdriver around so you pry equally from all sides.  Just work it up slowly.  As far as I know, it's not glued onto the shaft or anything, it's just a really nice tight Japanese fit. (Note: you may want to put a piece of paper or something between the screwdriver and the tach face so you don't mar up the face.  I didn't, and it didn't do too much damage, but I'm not overly concerned about "looks"...)

Take the black screws loose and the face will lift off of the movement.

Here's a shot of the movement itself.


Here we come to a divergence in my own story.  I couldn't find any writeups on the 'net about disassembling the movement, so I had to figure it out on my own.  And I did some things out of order, or at least, once I finally had it apart, I realized that I could have done it better.  So here my story will split.  Because I took pics as I was doing it wrong, my first story will describe the pics and the wrong way.  My second story will be my guess as to a better way to disassemble it.

Story 1: The wrong way 

(you should NOT be doing the steps in this order...)

Step 1. At this point, I foolishly removed both the screws holding the metal plate to the housing and also the flat nut holding the circuit board to the housing.  It's kinda tricky - you have to hold the brass barrel-screw while loosening the nut.  There may be a special spanner screwdriver to hold the screw, but I don't have one. I did manage to hold the screw with the tip of the corner of a paint scraper for long enough to loosen the nut with a pair of needle-nose (should maybe use a wrench).


Step 2. Now the D'Arsonval movement itself will come out of the housing.  The problem is that since I still had the leads soldered it, it made a huge mess with the springs. Yeah, I had to lift that brown circuit board over the shaft - that made a HUGE MESS (which luckily you can't see in this pic)

Step 3. Remove the screws holding the horseshoe to the magnet and pull the horseshoe off the magnet.  Then twist the actuator arm around counter-clockwise so you can get the coil off of the horseshoe on the left side (my horseshoe has a "2" stamped on the left side).  Again, with my leads STILL SOLDERED, it was still a mess.  Here's a picture of the actuator arm sitting on top of the horseshow after being removed.

At this point, I called it a night.  I didn't have my soldering iron, so I couldn't go any further without cutting something, and I didn't want to cut.  This was a great time for a nice, cold GUINNESS.

Step 4 (next day - with my soldering iron):  Unsoldered the leads, finally. (DO make a drawing of which side the respective wires go to).

Step 5. Unsoldered the outside coil of the bottom spring from it's joint on the circuit board.  This let me remove the circuit board and the top spring (the one that came loose at the center and caused all of this mess).

Step 6. Unsolder the bad spring from it's post on the circuit board.

look at that.  An evil spring... ;)

OK, that's it for my incorrect disassembly.  Here's what should be a BETTER WAY to do it.

Story 2: A Better Way

(you SHOULD be doing it this way)

1. unsolder the leads

2. unsolder the outer coils of BOTH springs from the posts on the circuit board.

3. Remove the flat nut that holds the circuit board to the housing and remove the circuit board. (Do make a mental note of roughly how far the brass barrelbolt sticks up, and how far down the flat nut is screwed down on it)

4. Remove the screws that hold the metal plate to the housing and remove the plate from the housing

5. Pick up the top spring when you drop it on the floor, then make a mental note to yourself that the next time you do this, you'll have the plate facing the floor and will pull the housing up off the top of it. (That's a joke.  But really, remember that the bad spring is now LOOSE inside the housing, so put the movement on the table with the metal-side down and pull the housing up and off)

6. Remove the screws holding the horseshoe on, then remove the actuator arm from the horseshoe.

technically, #6 may not be necessary - you may be able to do the soldering with the actuator still on the horsehoe, you'll just have to find a way to keep it from swinging around on you.

Also, when you pull the actuator up (in #6), there is some sort of plastic ball at the bottom of the shaft. I guess this is a self-lubing ball/bearing to keep the shaft easy to rotate. you might want to be careful with the shaft so you don't damage this ball.  It is a hard ball, but I don't know how much abuse it can take.

See, that's MUCH easier than how I did it.  And it doesn't make a mess out of the springs.

OK. We've got this puppy disassembled, now it's time to actually REPAIR IT.  It's not too hard, really.


First, find something to use for a spacer to hold the spring at the more-or-less correct height.  I used a bent piece of solder - it's the silver thing in the pic.   Just remember to remove your spacer before you reassemble the tach...

It's simple enough to solder the spring back onto the center post.  You SHOULD be able to look at the spring and see a bit of solder from where it was originally soldered on - that's where you want the post to be when you finish.  I soldered the post so that it was centered in the silver spot on the spring from the original joint.  I also added a bit more solder to it - it's the silver blob at about the 10:00 position in relation to the brass center piece. Just make sure you don't bridge between your solder blob and the brass center thing, that probably would be a Bad Thing. No, I'm not much of a soldering wiz, despite my IT background.  I didn't use silver solder.  I used regular 60/40 tin/lead (or maybe that's lead/tin) solder and Plumb Boy plumbing flux and an old $8 soldering iron from Radio Shack.  Didn't need long tips on the iron or anything fancy.

To get the actuator to stand up so you can solder it, drill a small hole (maybe 1/8" x 1/2" deep) in a piece of wood and set the "ball" thing down in it.  The actuator will rest on the coil, so use something to brace up the otherside and make it more-or-less level (I used the horseshoe and a quarter - worked fine).

You have now repaired your broken tach.  This is another good time to take a moment and reflect on life and on some of the supplier decisions made by the engineers at Honda.  The NH is a wonderful machine, but the tachs suck.



I could do it like the Clymer manual does, and say "For assembly, follow the disassembly instructions in reverse order".  But that wouldn't be much fun.  And I've still got pics to show.

remember to remove your spring spacer.

1. Put the actuator back on the horseshoe and screw the horseshoe back onto the magnet and plate..  The "2" faces up, and thread the coil on the horseshoe from the left side.

2. Insert the spring assembly back into the plastic housing and screw it in.

3. Put the circuit board on, screw the barrel bolt into the hole, then the wavy washer and flat nut on.  This part is tricky.  It's hard as hell to hold the barrel bolt while tightening the flat nut.  I finally managed to do it by putting the point of a 3-penny nail into one of the slots in the barrelbolt and holding that with one hand while tightening the flat nut with needle-nose in my other hand.  Not easy, but doable.  Try to get the barrel bolt to more or less the same depth as it was when you took it out, and also the flat nut.  I didn't measure or anything, just kinda eyeballed it.  If there is a magic-number for how far down it has to be (or how far is too-far), I don't know it.  The actuator should go around smoothly.

(sorry, no pic for this step)

4. Solder the outer loops of the springs back to the circuit board posts.  Do the bottom one first (assuming you've got the movement sitting with the metal plate down).  This part is more tricky than when you resoldered the center post, since you have to pull the springs a bit to get them to the posts, but being springs, the springs want to pull back.. I used a pair of tweezers to hold each spring while I soldered it.  Fingers got a bit hot, but it worked.  Also, just like the inner post, re-solder so that the old silver on the spring is centered on the post.  (if you are totally uptight, you probably used a caliper to measure the length from the post to the end of each spring back before you desoldered it.  I'm not that uptight, but it's probably a good idea if you've got the equipment.)

(sorry, no pic for this step either)

5. Resolder the leads into the proper holes on the circuit board. 


6.  Snap the housing back together, taking care to route the leads through their holder spots.

7.  Put the face back on.

8. Put the needle back on the shaft.  To do this, align the actuator arm with the marks you made on the housing and horseshoe, put the needle on the shaft so it's resting against the black stop-post, then gently but firmly push the needle back onto the shaft.  Unless you get very lucky (or figured out a gee-whiz way to make your marks),  the needle probably won't be accurate when you actually put the tach on the bike.  But that's a problem for later.

NOTE on broken needles. I broke mine.  You can see the bead of JB-Weld I used to put it back together right at the edge of the hub.  At first, mine was still partly attached to the hub, but while I was trying to put the JB weld down in the crack, the needle totally broke off.  ARGH!!!  But all is not lost.  There's a bit of a lip sticking out of the back of the hub, so just use the same piece of wood that you used to hold the actuator while you soldered the inner joint. Set the hub over the hole you drilled so it's flat against the wood, put JB weld on both broken ends of the needle, and put an 8-penny finishing nail under the end of the needle to hold it in place until the JB weld cures. Mine seems strong enough to withstand repeated smacks against the stop-post, but only time will tell if it will last long-term.(update: after a week of use, the JB weld seems to be holding fine.)

9.  Put the tach guts back into the white housing, and put the four screws back in to hold it.  You may have to press the leads out of the way so it will go in smoothly.


Adjusting the tach

At this point, we need to get a rough-estimate of how far-off our needle is, so take the tach out and hook it to your bike.  Don't worry about the 4 wires - just make sure they aren't grounding out against anything.  Crank the bike and see how far off it is from your normal idle speed.  Mine was on the low side - idle was registering ~200 rpm where my bike normally idles a tad over 1000 , and what sounded like 4000 rpm was only registering about 2000 rpm.  Oh, and if your tach doesn't work at ALL, well, I don't know what to tell you. 

To adjust mine (which was LOW), I took the tach back into the shop, took the movement out, held the HUB and pushed the actuator arm COUNTER-clockwise (ie - the actuator was a bit to the LEFT of my original mark on the horseshoe, so I moved it to the right).  If yours is HIGH, I guess you need to move the actuator clockwise.  There's some sort of tab like thing on the actuator arm that I pushed on.  Probably not a good idea to push against the coil.  How much do you need to move it?  I dunno.  Move it a little at a time, reassemble, take out to bike and check it.

If you really want to get better accuracy than just idle-speed, put the tach back into the silver cover, wire it in, put your headlight back in, and road-test it.  We all know (roughly) what our RPMs are at 55 MPH (a smidge over 3500 for me), so take it up to 55 and see where it sits on the tach.  Adjust accordingly.  I DIDN'T road test mine before I put the bezel back on, so mine is still a tiny bit low, but not enough to be worth hassling with the bezel again.

Once you have it as accurate as you want, you have only two remaining tasks - sanding/scraping the white shell to clean up the scarring, and putting the bezel and glass face back on.  This is perhaps the WORST part of the whole operation, because it is not only just as mind-numbingly boring as taking it off, but it's also aggravating because this time you can't use leverage to bend the metal, you have to use brute strength.  What I did was reassemble (remember the orientation of the black ring thing), then use the tip of a phillips-head screwdriver to bend the bezel lip.  Go slow, take your time.  Bend a section down, move the screwdriver 1/16" and bend that section.  Make 2 or 3 passes around the perimeter instead of trying to get it all done in one pass. Make sure the bezel is holding things together tightly.  I got a blister on my finger from this part. Very repetitive and makes your fingers sore.  Also, the bezel lip will be DOG UGLY after you bend it back down.  I dunno how to avoid this.  You might also want to put a small bead of silicone caulk around the bezel lip to help keep moisture out of the tach.  I haven't yet, but if I start getting condensation, I will use the caulk.

Now reassemble the tach into the silver housing, mount the instrument cluster, wire it into the headlight bucket and you're done.  Remember, when re-attaching the 4 wires, just match up the colors.

That's all there is too it.  Was it worth it to not have to pay BikeBandit $504.71 for a new one?  Hell yes. Would I have done this if I found a working tach on eBay for $75?  Probably not.  Would I fix yours for $75?  Maybe, if you ask nicely and promise not to bitch if I break the needle.   No, sorry, I don't fix tachs anymore. It's too tedious. Except for the bezel and the needle, it's not really a hard fix, but it is tedious.

Dave Doster

dave at nighthawk750 daht com (if you haven't figure that out already)

15 Sept 2007