Smiths rev counter needle waves / drops

[jko_78]

Around ~3-4000 RPM the needle of my Smiths rev counter drops to 2-3000 RPM and picks up again, but only intermittently. It does not seem to do that below those revvs and when it doesn't do that, the needle is very stable otherwise.
It's had this for a while, but then stopped working completely. So as it wasn't working at all when we got the bike, it turned out to be due to the slotted bit in the drive being worn/broken, we replaced that and it now does mostly work other than that irritating occasional drop. I thought the drive had worn due to a broken or heavily turning cable, but the cable has been lubricated (some oil coming out of the lower end) and can be easily spun between two fingers. Just not fast, of course.

Somehow my feeling is that, since it's so intermittent, it's the instrument itself, I've had bad cables on other bikes in the past and they would have a spot where there was more friction if you rotated it with 2 fingers, and around certain revvs the phenomenon would always be there -but it's not very scientific, I agree.

Any tips or suggestions other than replacing the cable and/or sending the revv counter to a specialist...?

edit: as you may recall the bike had an accident a long time ago, the original instruments were completely smashed up so this was a replacement and not damaged in that crash -although as ever with second hand things, history unknown.

 

[Vince]

Many years ago, I was having speedo issues, so I spent a stupid amount of money getting it rebuilt, only to still have that issue. It turned out to be missing teeth in the speedo drive on the front wheel. Sorry, that tail was pretty unhelpful. In the end, it was fixed and I suppose the rebuilt speedo didnt need future work.

 

[Ernesto]

so this was a replacement and not damaged in that crash -although as ever with second hand things, history unknown.

Smiths clocks that haven't been used for a long time or even NOS ones need to be cleaned and lubricated before use.
Otherwise they might even totally break down after a short time.
Same if they had been stored upside down.
I can recommed tellerwerk.nl for work on them.
Ernesto

 

[MarnixSFC]

When using a rev counter cable for ND clock in combination with a Smiths instrument, there is no good fitting of the square shape inner cable end. It will work a while but at some point the cable will slip, initially now and then, but will get worse, until it doesn’t work anymore..

Marnix

 

[jko_78]

Thanks all!

I've had a second look at the cable and instrument last weekend; based on Marnix suggestion I had a good look at the cable end, it seems to be in good shape optically, as in, does not seem to be worn/damaged visually. However what was interesting is that after I had the cable completely off and re-connected it, suddenly the needle seems to behave now. Might have been a case of the cable not being inserted well enough in the first place, though I have no idea how that could happen with a square end...? I'll keep an eye on it but it annoys me when I can't find a root cause
Edit: we did work on both the drive and replace the instrument suspension rings -perhaps we just didn't assemble it correcty and the cable was not full inserted at the instrument side or something.

@MarnixSFC is there a way to recognize what cable there is? Length of the square end sticking out at the end for example?

I'm still thinking about Ernsto's idea to send both instruments off to tellerwerk this winter, for a technical checkup/maintanence. (and perhaps have the needle orange again...)