B40 Speedo - wots the right one ?

[hoogerbooger]

I have the head out of the case, but have not tried dismantling ....as yet.

I've blown what out dust I can, but the symptoms persist. As the photos show there is a general layer of crud/corrosion  on everything.

Thinking about the symptoms (described in earlier posts) as the screatching is not continuous and is combined with the needle jumping across unreal speeds surely it must be the drag cup getting fouled somehow ? and not the drive spindle ??

Just had it running on a drill at 20-30 for 30 secs ok, then when I dried to increase the speed  sypmtoms occurred.  The speed at which symptoms starts varies. May actually be the acceleration that kicks it off.


So can I double check I should be able to dismantle to remove and clean the drag disk/cup (leaving the magnet in place) without having to get it recalibrated

Previously I was advised:
"It's only when you need to get at the drive spindle or the odometer mechanism that you are likely to disturb the calibration".

[AdrianS]

I stripped the speedo fitted to my D14 Bantam. It was reading about 60 at 20 mph.
Not much inside them. Mine had a rotating magnet which induces a rotating force on the plate attached to the needle.
Resistance is supplied by the watch spring attached to the spindle.
Things to fail: magnet looses force, spring breaks or weakens, distance from the magnet to the plate changes.
I was only interested in the speedo reading correct at 30 so through trial and error I just moved the needle on the spindle to read correct at 30 ( checked by following someone doing ,30)

The speedo mechanism shouldn't make any noise. The mile ometer is best driven and could make a noise if faulty.

By the way I did manage to prise of the chrome retaining ring to separate the speedo and replace it without too much damage.
Also I did buy a cheap Indian speedo but this required a different cable asci think they were for a Royal Enfield.
It was very inaccurate and rejected it!!

[hoogerbooger]

(bump)

can I double check I should be able to dismantle to remove and clean the drag disk/cup (leaving the magnet in place) without having to get it recalibrated 

[AdrianS]

If you clean up the internals then you will need to get it re calibrated. If you are just attending to the mile o meter part then you shouldn't need to recalibrate. The speedo is very sensitive to the spring tension, magnet to plate distance, and strength of magnets and I suppose any friction within the system!

[hoogerbooger]

From memory, I think the needle rotates in a self lubricating brass bearing. However, if it's not that, it may be a build up of crud stopping the aluminium plate attached to the needle from rotating freely. Either way, if you pull off the needle and unscrew the dial, you can then get at the needle mechanism and clean and lube it as necessary. It's only when you need to get at the drive spindle or the odometer mechanism that you are likely to disturb the calibration.

As a reminder my speedo squeels and the needle will dart across.

If it is not just crud build up catching the drag plate and rather it's a worn spindle bearing ( so that there's some play and the magnets catch the drag plate some times..........then is that something I can potentially repair myself ....or will it need a new part....if they can be got

( as it is the needle is still resisting removal & I'm awaiting arrival of tools to increase my chances  in this life & death struggle)