Speedometer Calibration

[Paul H.]

My new to me 1984 R65 has a MotoMeter speedometer W1318. It is not the original and shows less than 5k. It works fine except for the fact that it is far out of calibration. At 50 MPH it reads 62. I have found discussion of how to re-calibrate by increasing the tension on the coil spring. The discussion was for a different model. I have it apart and can increase the tension by moving the end of the coil a bit or it seems to me simply by moving the needle CCW a bit on the stem will achieve the same result. It has a positive stop pin at 0 so lifting the needle moving it a bit CCW and returning to the stop position should increase the tension. What am I missing? Final drive is 32-9, proper tire, and the odometer seems to be correct. Thanks Paul H

[Bob_Roller]

Which speedometer do you gave, the 85 max, or the 120 ??

[Barry]

1318 is the correct speedo ratio for your final drive as confirmed by the odometer reading correctly. 

All airhead speedos seem to read well over the actual speed by up to 10% plus a few mph but yours does seem much more than usual.
Mine wasn't so far out so I recalibrated it by simply moving the needle as you describe by first lifting it over the stop, marking the rest position on the unseen edge of the dial and then replacing it by an estimated amount CCW. It was a process of trial and error and I had to test it out a few times before properly assembling the crimped bezel. If yours isn't a crimped bezel then you have it easy. What I did was aim for spot on at 30mph and then tolerated it being just a few mph fast at high speeds. 

As to whether moving the needle produces the same effect as moving the anchor of the hair spring, I believe moving the needle corrects a zero error and moving the hairspring corrects a span error. If you want it spot on at every speed you will likely need to do both.

What I did was vast improvement but prepared for the bike to feel slower !

[Paul H.]

Thanks Barry, I took careful note of the needle position at rest before starting so moving it should go smooth. I took the coil spring end loose and wound it back about 1/8 inch.That moved the resting position only slightly so I am going to try a slight needle rewind also. I'll take a test ride before final instrument assembly, it is a crimped rim so I only want to do that once, to see if I made any progress. Moving the needle is very much easier than the coil winding. No need to remove the face and the coil is VERY delicate. Fingers crossed, we'll see.

[Barry]

... it is a crimped rim so I only want to do that once, to see if I made any progress.

I couldn't believe the rim was steel, so quite difficult to uncrimp and re-crimp again.  What I found a challenge was re-crimping well enough to maintain a water tight seal. I finished up using a drill press and a bit of a jig to press the body lightly into the rim seal while I did the crimping - a 3 handed job.

[Paul H.]

"What I did was vast improvement but be prepared for the bike to feel slower !" Amen to that Berry

My re-calibration went well. Tested yesterday and at speedo 50 GPS 52 and speedo 30 GPS 29. Close enough for government work. I am not going to chance taking it apart again. The last challenge is getting the metal bezel back on and crimped watertight.