Introduction: How to Open a Honda CB/CX/GL Style Tachometer and Speedometer

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One day while riding my 1981 Honda GL500 I had the miss-fortune of having the screws that hold the dial face of my tachometer un-thread themselves after 29 years of vibration and cause the face to spin around freely inside the case. Unfortunately the case is not simply screwed together, the front and back halves are held together with a band that has to be removed to split the case apart to fix the dial face. So that is what this instrucatable covers, how to remove the band and take the tachometer apart as well as the speedometer.

This should also work for the Honda CX500 as it uses the same units as well as the early Goldwings and 70's through early 80's CB series bikes with the same style tachometer and speedometers.

Step 1: What You Need


Materials:
- Tachometer or speedometer that you want to take apart for some reason

Tools:
- 1/4" flat bladed screw driver with a tip that comes to a fairly fine point as it will have to get under the edge of the retaining ring to pry it up
- and a pair of pliers

Step 2: Removing the Ring

1) Stick the edge of the flat screwdriver blade under the back edge of the retaining ring, do this on the back because it doesn't get seen when the unit is installed on the bike so if it gets mangled up a bit it doesn't matter.
2) With the length of the blade at an acute angle to the ring, see first picture, gently twist the screwdriver to bend up the edge of the ring. Carefully do this all the way around the ring until it is fairly well straitened out, you might want to make two passes to get it opened up all the way, you can also use the pliers after you have gone around once with the screwdriver.

3) Gently use the screwdriver to push, pry the retaining ring over the ridge in the upper case.

4) Once the ring is off, simply pop the two halves of the case apart.

* Note: If you are taking apart the speedometer, use a roll of tape to hold the case above the table to ensure that you don't accidentally bend or damage the trip meter knob. Also before separating the two halves of the case, remove the two screws from the back that hold the mechanism in place.

Step 3: Reassembly

Once you have fixed your tachometer or speedometer, or thoroughly tinkered with it to figure out how it works :) it is time to put it back together.

1) Before putting the unit back together, take and make sure the mechanism is clean and the screws holding the dial face on are nice and tight.
2) Using the pliers, flatten the ring out some more to make it easier to slide back over the cases.
3) Place the ring over the top half of the case with the pealed open edge facing the back of the case, place the back half of the case over the front and slide the ring down and over the ridges in the two cases so that the front of the ring is seated nicely all the way around the ridge on the front case half.
4) Use the pliers to bend/crimp the ring back down all the way around the case. It works best if you put the jaw of the pliers that is on the front side of the case all the way up against the case and the jaw on back is on the edge of the ring, rock the pliers back as you squeeze the pliers to gently crimp the ring back down. Go around the case again after the first pass to make sure the crimp is nice and tight.
5) Reinstall the clocks back on the bike and test them.

Step 4: Fixing the Tach and Speedo

As you saw on the intro page the reason I opened up my tachometer to re-attach the dial face but I also had to take the speedometer apart because I crashed my bike and smashed the speedometer case. In order to fix the speedometer case I used a spare tach case, I sold my spare speedo, and transplanted the guts from the speedo into the tach case. This required drilling a hole in the side of the donor tachs, front case half for the trip meter knob to go through. To drill the hole, I measured where the hole would be and slid the inner liner out of the new front case. I used a center punch to mark where to drill the hole and a step drill to make it after using a pilot drill to start the hole, I drilled the pilot hole before separating the inner liner from the front case. The hole in the outer section of the case needs to be 1/2" for the knob to fit through and the hole in the liner has to be about 3/4"