[Arizoni]

Here are several links to topics on this forum that talk about fixing the RE's speedometer.

Once you get into them be sure to look at all of the pages.  There's a lot of interesting information there.

https://forum.classicmotorworks.com/index.php/topic,23491.msg270161.html#msg270161

https://forum.classicmotorworks.com/index.php/topic,17430.0/all.html

[Yamahawk]

Thanks for the links, Arizoni, it gave me the confidence to remove the bezel ring and see what's what! I found the hairspring has one end staked through a hole, with a tiny brass pin. I pulled the pin, and then grabbed the spring end, pulling it further through the hole about 1/4", and re-staked it with the teeny tapered pin. I now have more spring tension, and have yet to try it. As I started the bike, it ran for 10 seconds, then quit, and I haven't been able to start it since... so, my speed test to see if I am close, will have to wait until the bike starts and I can ride it lol...
Charlie

[Yamahawk]

PROGRESS>....
    I have dismantled the speedometer, adjusted it, and took it for a test drive. I regained 5mph from the 20mph over-speed it was reporting. I 'should' have left it with the greater tension I had when I first pulled the spring through the hole, but I thought it would be too much, and slackened it off. Now, I have to repeat my process, and give it more tension, but I am on the right track! Stay tuned!
Charlie

[Stanley]

While following the method of refitting the needle with more spring tension, I think I did a passable job of re-calibrating my speedo until I was putting the bezel into place. I cracked the lens and just spent time searching the Interweb for a replacement. Does anyone know of a source for 3 inch lenses? I found various other sizes and will keep looking. I may have to turn some plastic on the lathe, but it's hard to find thin Lexan.
Boogers!

[hpwaco]

Try a clock supply place like Timesavers in AZ.

[Stanley]

Thanks, but the clock glass isn't available in 3 inch, so turned a piece of Home Depot Lexan on the lathe.
My speedo is now as accurate as can be. It was reading a consistent 12 MPH fast. Other than removing the bezel and glass, the rest is easy. I simply pulled off the needle and replaced it CCW the same number of degrees it was reading higher than than it should.  I simply bent it up slightly to settle above the stop peg. Testing was a simple ride with the glass off, stopping to fine-tune the needle angle until it matched my bicycle speedometer at different speeds. Easy peasy. No need to even remove the speedo face or housing. I rode home to remove the speedo, crimp on the bezel and Bob's now my uncle. Now I can use that bicycle speedo as a tach on my lathe.

[Yamahawk]

Cool Stanley! What year is your Enfield? Mine's a 1996, and for the life of me, I couldn't get the needle to pull off the shaft. So, mine has a brass tapered peg (VERY small) in a hole that stakes the outer end of the 'watch' coil spring on the needle shaft, and I added tension by pulling the spring a little more through the hole, and then re-pegging the spring with the brass tapered peg. I am now down to 10 mph instead of 20 mph, so I will try it again when I get the chance to do so.
Charlie

[Stanley]

I have a 2000 IB. After I decided to risk a bad outcome, I evenly heated the disk of the needle with a light soldering iron and pried it off with two screwdrivers against the two face-attaching screws.  Once it was off, it went on and off with firm pressure. Small soft leather pads protected the face from scuffs.

That hairspring looked too dainty for me to touch. Kudos to you!