Author Topic: Speedo reading out  (Read 119 times)

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Phil C

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Speedo reading out
« on: 10 November, 2019, 10:30:30 »
Morning all,

I'm not going to get round to sorting this just yet, but plan to look at it in time.

My speedo is overly optimistic. I haven't established how far out it is, but it says I'm going a lot faster than I really am.

I guess this is not uncommon. What is the most likely cause?

Phil.

Davidat19

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Re: Speedo reading out
« Reply #1 on: 10 November, 2019, 11:25:02 »
The likely causes are


a. It was built in Small Heath.
b. Its been pissed about with over the years.

Check you have the right number on the speedo. Check your cable is LIGHTLY lubricated and free turning. Check the gearbox at the rear is correct.

Phil C

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Re: Speedo reading out
« Reply #2 on: 10 November, 2019, 11:55:51 »
Sorry to be a bit dim, but could you expand on:

 -  "check you have the right number on the speedo"? Do you mean check it's the right model for the bike?

 -  "check the gearbox at the rear is correct"?

Thanks in advance.  Phil.




Phil C

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Re: Speedo reading out
« Reply #3 on: 10 November, 2019, 12:33:56 »
Re having the right number on the speedo, I've just checked RR vol 2, and confirmed that I do have the right one for the bike (1965 B40F) : SSM 2001/02  1600.

Could you explain what you mean about the gearbox at the rear being correct?

Phil.

Phil C

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Re: Speedo reading out
« Reply #4 on: 10 November, 2019, 17:54:33 »
Sorry, yes, obviously you mean the little speedo gearbox at the back wheel. I'm pretty sure it's the right one.

So if both the clock and the gear unit are the correct ones for the bike, what is a likely reason for a false reading?  The gear unit being worn, perhaps?   

Phil.

JulianS

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Re: Speedo reading out
« Reply #5 on: 10 November, 2019, 19:03:30 »
Suspect the speedo needs an overhaul.

Phil C

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Re: Speedo reading out
« Reply #6 on: 10 November, 2019, 19:13:34 »
Thanks, Julian. Is that a diy job for the likes of me?

Actually, in my previous post I said the gear unit was the right one for the bike. I based that on the fact that it was the roundish-shaped version (see photo attached.)  But it seems from RR vol 2 that there are several of those with different ratios.  Is it possible that I have the wrong one for my bike?  (1965 B40F)

Phil

JulianS

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Re: Speedo reading out
« Reply #7 on: 10 November, 2019, 19:33:11 »
If you feel confident there is a book which explains.

https://www.ebay.co.uk/itm/Smiths-Magnetic-Speedometer-Speedo-Repair-Tachometer-Revcounter-Repair-save/323749514261?hash=item4b60f98c15:g

The first challenge is removing the rolled on bezel, then having dealt with the insides the final challenge is rolling on the replacement bezel.

hoogerbooger

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Re: Speedo reading out
« Reply #8 on: 11 November, 2019, 15:16:10 »
Phil

I took my speedo apart & spent some time considering calibration .

My advice is if the needle is smooth and doesn't flicker back and fore; you can't see any flaking paint inside; & it doesn't make noises, then just get used to it being over optimistic.
(Just work out where 30MPH, 40MPH & 50MPH are roughly ( by following a mate in a car) should  you really want want to try and get a speeding ticket).

Alternatively send it to a professional for a service and recalibration.

Calibration is the hardest bit to do yourself and needs a test rig set-up,which can be made....but I decided wasn't worth it. It also needs to be out of the case. Taking the bezel off and replacing it ( new replacement will probably be required) is doable, but a pain.

Oh yes, you can check you have the right gear box by undoing and pulling out the cable and inserting a large match of similar size to the squared off cable end. bend the end of the match 90 degrees to make a little pointer. Stick the bike on the centre stand before you do this and make sure wheel is off ground.Then with the bike in neutral you can rotate the wheel by by one, two, three turns and count the number of turns on the match stick.

Rupert ration Vol 2 will tell what ratio the gear box should be.

( be careful when you reattach the speedo cable to make sure it seats well in the gear box before tightening up)

« Last Edit: 11 November, 2019, 15:28:06 by hoogerbooger »

Phil C

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Re: Speedo reading out
« Reply #9 on: 11 November, 2019, 15:53:30 »
Very helpful. Thanks very much. I'll leave it for now, but I have at least learnt something about the subject. Might have a bit of a fiddle around in future at some stage.   Phil.

AdrianS

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Re: Speedo reading out
« Reply #10 on: 12 November, 2019, 09:47:30 »
I used a chap near Mansfield who advertises in OBM.
Came back repaired/restored. Not cheap to have done.
The other alternative is to buy one of the Indian copies from fleabay but these can also be hit and miss and some need a different speedo cable.
I did originally take mine apart and moved the needle so when I was doing 30 it read 30. The needle is a friction fit on the spindle. I sent it off for calibration and repair because I chewed up the sealing chrome ring!