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