Speedo adjustment ?

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Jul 18, 2004
Hey guys & gals,

Took my beloved to Paris this weekend. Translation: I rode my Norton to the Classic bike rally in Paris, Ontario. 8)

My speedo is reading about 10mph too fast - any suggestions - are Smiths adjustable?
Speedo adjustment ?

Here she is resting after a day's ride.
Yes you can but it requires that you take it apart. A magnet and an alum disk inside are adjusted for gap. The closer they get the faster it reads. There is a good link about this I will try to find.
During early testing, we had a speedo that was calibrated for 1000 revolutions per mile (who knows why) and we were using the Atlas speedo drive which was 1600 revs/mile. As a result, the indications were 1.6x actual speed. Above about 60 mph, the speedo was pegged and we had to rely on the tachometer.

I was lucky that I never got stopped for speeding in all the test miles (probably 15,000 oin the street) that I did!
adjusting a Smiths speedo

My speedometer is doing the same thing ~ 10mph faster than I'm going. I've compared to the radar speed signs set up locally (my car's speedo is exactly what the radar says). You can drill a hole on the back side of the speedo case to get at the adjuster screw, but I haven't had any good luck correcting mine.
Mine's right on the money. Guess I got lucky on that. The speedos on my other bikes all read about ten percent high though.

Is it 10mph faster at all speeds rather than a percentage ? Mine have always been pretty good and in line with the tacho. I do know that the chap who rebuilt it always calibrated them on an old Smiths machine.

Hertfordshire police were good enough to check the accuracy some years ago and their radar showed 101 mph when I was reading a needle's width faster.

If you don't want to recondition the speedo, you'll have to change the rear wheel size :)
Try fitting a bicycle speedo (cheap - inexpensive in colonial speak) they can be calibrated from the tyre circumference and the drive doesn't break. You can fit the magnetic pick up on a bracket bodged up from an old spoke on the disk thru' bolts.
works fine an it also tels you the time!
speedo calibration

For me I just want it to read the correct speed. It's embarassing getting passed when it says 70mph and really only doing 60. I've turned the adjusting screw inside, but doesn't really change. Since both tach and speedo needles started bouncing again about a year ago, I know they need to go back for another rebuild - only lasted 9 years and 16,000 miles since the last rebuild.
Thanks for the input - I did a rolling check at 100KM/H with a friends bmw sedan - so I don't know if is is all over or just in the upper range. I had a hunch I wasn't going as fast as I thought. The guauges are freshly overhalued so perhaps they just need some tweaking.

Hello all,


this site should answer all the questions, for those that are confident in delving into the mysterious world of the SMITH's

Now another area than can make the speedo, or tacho ready faster, it an inner cable that protrudes out of the outer case too far. Nasty as this destroys the instrument eventually. I had a nice newly restored set of gauges, that went beserk before my very eyes, on a trip from Sydney to Melbourne. The tell tale signs of brass fillings in behind the glass gave the game away.
So check that your inner cable does not stick out anymore than 7/16" when seated properly at the top. Also sometimes to longer tail at the bottom, or not enough square at the bottom can cause this.

Cheers Richard
Speaking of cables..

My speedo stopped working after 350miles. It came down to the fact that the cable at the gear end was too thick and not engaging into the worm gear - just pushing against it where it was slightly rounded at the tip. It eventually rounded out the end of the gear. I squared off the tip, thinned out the square so it would fit into the gear and trimmed down the sheath so I was getting a good 1/2" of engagement into the worm gear.
Accuracy aside, it seems to be working fine (knock on wood).
I have a feeling "accurate Smiths" is an oxymoron - like "reliable Lucas" :p
Speedometer rebuild and calibration

RichardS said:

Does anyone have an updated link for this document on Smiths speedo repair? It appears to have been moved or removed from this server. Also, any additional information about how to recalibrate a later-model Smiths speedo (on a 74 Commando) and where I can buy a new bezel would be greatly appreciated. Thanks.
Re: speedo calibration

illf8ed said:
speedo needles started bouncing again

That isn't normally a Speedo/Tach problem. Lub the cables so they turn without grabbing, leave the upper inch or so of the cable dry to prevent the oild getting into the instrument and ruining it...and the bouncing needle will normally go away, for a couple months at least, till the cables need to be lubed again. Been lubing my cable and fixing bouncing needles that way for now about 90 thou on the speedo, and 120 thou on the Tach. Mine might read a bit incorrect now,as I read 4 to 4.5 grand or so at 60/70 mph...but they don't bounce... :wink:
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