Repair of BMW R90S /6 /7 Odometer Reset

I find it difficult to reset the trip odometer on my R90S. The reset knob is in an awkward position, my left hand is arthritic, and I can never remember which way to turn the knob.

After I turned the reset knob the wrong way on several occasions, the last time I apparently twisted off the square shaft part of the plastic reset knob.

An article in Wind Noise (the R90S Owners Club magazine) about re-painting the hands on the clock inspired me to try to fix the odometer reset myself. Opening it up is trivial (just remove the dozen or so screws), and inspection showed that I had broken the square bit off the business end of the plastic reset knob. I drilled into that broken plastic piece, put a screw into it, and pulled it out of the hollow metal reset shaft.

A search of Snowbum's site, Airheads mailing list, and Googling the entire InterTubes brought up a couple of old posts on the Airheads mailing list, from somebody who repaired his odometer reset by drilling out the plastic knob and glueing in a piece of square "key" material. But I could not find anyone who had addressed the design flaw that allows you to break the reset knob by turning it the wrong way.

I decided to repair my speedo by adding a spring clutch. First, I found in my spring junk box (doesn't everybody have one?) a spring about 1 cm long that is a snug fit over the steel reset shaft and is wound such that turning the spring counter-clockwise causes it to grip tighter (turning it clockwise causes it to relax its grip and slip).

To keep the spring from slipping down the shaft (towards the front of the speedo, so I guess that would actually be "up" when the whole thing is installed in the bike), I found a plastic cylinder that was about the same size as the spring. If you must know, it was the "roll" around which dental floss was wound. (Yes, I keep old dental floss containers and other random bits of plastic. "Someday, son, all this will be yours".)

I bent the last half turn of the spring up at 90 degrees to the plane of the face of the speedo. I cut a slot in the end of the plastic reset knob using the cutoff wheel of my Dremel. It turns out to be an easy press fit onto the bent end of the spring. I found an E-clip in my junkbox that fit in the slot at the end of the plastic reset knob, so it can't be pulled out of the back of the speedo.

It works. Turning the knob counter-clockwise (when facing the back of the speedometer) causes the spring to tighten up and drag the steel reset shaft along with it, resetting the odometer. Turning the knob clockwise causes the spring to relax its grip and the knob and spring just spin harmlessly.

Copyright © 2009 William F. Dudley Jr.

Comments? email bill at dudley dot nu


view showing white spacer and spring clutch
view showing "back end" of spring clutch bent to meet plastic shaft
view showing plastic shaft mated to spring clutch
another view showing plastic shaft mated to spring clutch

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