Tachometer, Speedometer, and Odometer Calibration

BMW odometers tend to be quite accurate, and all the speedometers EXCEPT the 85 mph ones (which are usually accurate), tend to read high by 6 to 12%.  This is ON PURPOSE by BMW. See the article hyperlinked just below, which is more detailed and has the information on why the inaccuracy, and MUCH more.  

Recalibrating a speedometer is a touchy job, of messing with such as hairsprings, and is best left to an expert.   

Speedometers/odometers have W ratios printed on the face, and they must correspond to the rear drive ratio, see the charts on the author’s website, which is more expanded than on this airheads.org website.   The following hyperlink to the author’s website has all the information you would want:

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Speedometer Repair

Thanks to all esp. Paul Glaves, Jeff Saline, and Randy Mallon

After some probing I found the upper RT silver gear that transfers drive from the total mileage to the trip odometer to be loose on the shaft and causing the trip odo to run intermittently. Using minimalist approach and a tooth pick I first carefully dipped the toothpick in alcohol and cleaned the shaft without disassembly. Steady hands and a watchmakers magnifying loupe helped. When that dried I put a drop of liquid crazy glue an a piece of plastic and using a toothpick I dipped it in glue and than transferred small amount to the shaft above the gear keeping it upright so capillary action will draw it downwards. I am now considering a good spot to drill a 1/4 inch hole and put a Gortex patch over it to try to get rid of fogging.

Jeff Saline cautions: One thing I don’t remembering anyone commenting on is allowing super glue the opportunity to out gas outside of the instrument housing. I haven’t ruined a lens yet but understand that if you use super glue and immediately reassemble the instrument housing the super glue will out gas and fog the instrument housing lens(es). I was repairing a high beam indicator blue lens the other day and have had the instrument out gassing for 6 days now. I recall hearing 24 hours is enough time

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12 Volt Clock Light

Ever tried to see what time it is while you’re moving down the road after dark? No, I’m not talking about taking a peek at your Timex, but at your ‘bar mounted time piece, whether it be a bicycle computer or one of the purpose built jobbies that BMW used to make for the airhead GS. If you did, chances are all you saw was a black blob instead of illuminated numerals. Or, if you’re savvy to the little LED jobbie that Sigma makes for their bicycle computers, you fumbled around in the dark looking for the tiny button, hoping you could find it with your gloved hand. That was my situation after I stumbled across the little gem in Aerostich’s catalog, but I wasn’t willing to put up with the switch and battery replacement routine that went along with it. I know just enough about electronics to be dangerous, which was just enough to rig up a 12 volt LED and wire it into the bike’s harness. All that was needed was the LED and a resistor wired in series with it to limit the current through the LED.

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Ampmeters versus Voltmeters

I see little reason in having having an ammeter permanently installed on any BMW motorcycle, unless you have special circumstances. I foresee several drawbacks, not the least of which is a potential fire hazard, which includes burning up your bike’s wiring; besides the usual situation of LESS reliability with many modifications; especially with added electrical items.  I will lay out the benefits, and the problems, for both ammeters and voltmeters. The GEN lamp provides quite a bit of information if you interpret it correctly….but it may not be enough FOR YOU.

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