Around 10 years ago, I found an old motorcycle headlight that had a speedometer built into it. It was really cool piece and I planned to incorporate it into a motorcycle build I was working on. The headlight/speedo was off an old Bridgestone motorcycle (not sure of the year or model), but the odometer was barely legible as was the left side of the speedometer. To address this, I needed to get the speedometer apart. Keep on reading to see the process. This procedure will work for almost any mechanical speedometer. The newer speedometers are back lit through the gauge face and night time results will not turn out as well. This speedometer is back lit from around the gauge face.
Once you have the speedo out of it's decorative cup/housing, lay it on the table face down. Using a small screwdriver, gently pry the lip of the trim ring up. Work your way around the gauge, careful not to pry too much or you could possibly tear the thin metal. When you get the lip pried up all the way around - remove the trim ring, glass, and inner bezel (if applicable).
Once again, lay the speedo face down and remove the screws holding the inner mechanism to the housing. These screws should be on either side of the cable stud. Turn the speedo back over and lift the mechanism out of the housing.
Clamp the speedo mechanism in a vice, and using two small screw drivers, gently pry under opposite sides of the needle. This needle is metal. Other needles are plastic (thus more fragile) and have metal in the center. The needles are a press fit on a smooth shaft. The first time I removed this needle - it took a little bit of force. The second time - it slid off much easier.
This is how my speedometer looked - only much dirtier. One of the screws that holds the face plate had been missing for who knows how long and the plate had rattled around and enlarged the left screw hole big enough that I would have had to use a washer to hold it in place. We'll get to the solution shortly.
This is what the mechanism looks like without the face. You'll notice that the odometer is set to 000000. I reset it. I do not advise doing this. In my state, vehicles past a certain year are mileage exempt. Check your local laws before resetting your odometer.
I took the old face plate and scanned it on my computer. I used the highest resolution to get the best quality. Using a photo editing software - I cleaned up the image. At this point - you can do whatever your heart desires - different colors or fonts.
***Suggestion: Do not leave the holes white on the image - make them the same color as the rest of the gauge.
A buddy of mine suggested doing a turtle and rabbit like on a lawnmower. Of course you can clean it up and make it look original. It's all up to you. I decided to go a little different route. I added some noise to make it a little grainy. I knew it would not turn out perfect and this would help mask that.
Now for the solution to the enlarged hole. I had a guy cut out a new face plate on his water jet. He didn't get the middle hole for the needle or the rectangle hole for the odometer exactly in the correct spot so I had to enlarge them a little.
I printed out my new face plate on some good photo paper. I cut it out, but left the 4 holes filled for the time being. I used 3M super 77 spray adhesive to attach the paper to the aluminum plate. I let it dry, face down, with some weight on it. Once completely dry (~15 min) I used a sharp razor knife and cut out the holes from the backside, using the aluminum plate as a guide. I had to touch up around the screw holes with a sharpie because the image didn't match the plate exactly. *This is why you leave the holes on your image the same color.
At this point, it's basically reassembly. The needle was originally white, but I sprayed a few coats of orange on it. Once it was dry, I just positioned it as close to the first tick mark and pressed it on with my thumb. Here it is with the inner bezel on. Now is a good time to hook up the speedo cable, chuck the other end in a drill and make sure the needle will move and return to its original position ***drill has to be in reverse*** You may also use a 9V battery to power your gauge light to see if the results are satisfactory.
Clean the glass so it's spotless, especially on the inside. You don't want a finger print staring you in the face once you get this thing sealed back up. Set the trim ring face down. Insert glass (in the proper direction) and the inner bezel. Set the housing face down on top making sure the bezel is lined up properly. Use a soft faced mallet and fold the trim lip over in four corners (corners on a circle - right) to hold everything together temporarily. Make sure everything is lined up, then proceed in crimping the trim ring on. I used a make shift punch with a large face and no sharp edges. Work your way around the gauge and seal that sucker up.
Here it is - all reassembled. You may be able to see the specs of dirt that are stuck to the inside of the glass. I'll use compressed air through one of the lighting holes in the back of the gauge to try to get that clean. I'll probably use a small bead of silicone around the trim lip that was pried up, just to help keep the elements out a little better.
*NOTE: I posted this write-up on a motorcycle forum back in 2009. I just went to reference it and realized that all the photos were hosted on a site that isn't friendly with third party hosting anymore, so I decided to repost it here so that others may benefit from it. Keep in mind, with the variety of knowledge and skills that are freely shared these days, as well as the availability of new technologies and equipment, I would have done some things differently now.
Unfortunately, life got busy and I still haven't finished that motorcycle build. Until then, I have this little gem safely packaged away until it's day to shine.
Thanks for reading.