Author Topic: Jerky Speedo?  (Read 882 times)

Offline AndyDenmark

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Jerky Speedo?
« on: 07.08. 2015 20:55 »
Hi all

The speedo on my Golden Flash seems to move in an extremely jerky fashion. It is a smiths Chronometric as far as I can remember without going out to the garage *smile*. Is this a common feature of them or does it suggest mine needs attention.

Thanks

Andy

Online RichardL

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Re: Jerky Speedo?
« Reply #1 on: 07.08. 2015 21:26 »
Andy,

You can find (out there on the web) a very detailed explanation of the workings of the the gears and governors and tapered post, etc. within the speedometer, but I think it boils-down to the chronometric needle making slight jumps up and down as it catches up with the speed sample measured by the mechanism. This may not be the best way to say it, or be spot on regarding the workings of the clock, but this is how I basically understand it. I will be quite happy to read other explanations myself.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Online Triton Thrasher

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Re: Jerky Speedo?
« Reply #2 on: 07.08. 2015 21:37 »
The needle of a Chronometric is supposed to move in sudden jumps.


Online RichardL

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Re: Jerky Speedo?
« Reply #3 on: 07.08. 2015 21:58 »
Thank you, TT. I forgot to mention that the little jumps are normal.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline sparx

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Re: Jerky Speedo?
« Reply #4 on: 08.08. 2015 07:31 »
The needle isn't directly connected to the drive cable.
 If the fluctuation is rhythmic it's usually caused by too tight a radius on the cable at the head end, or a dry cable with too much drag.
  If the needle hangs back then jumps up as speed is increased it suggests the speedo itself is at fault.
Dave
Peterborough (UK)

Online Triton Thrasher

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Re: Jerky Speedo?
« Reply #5 on: 08.08. 2015 11:08 »

  If the needle hangs back then jumps up as speed is increased it suggests the speedo itself is at fault.

No it doesn't.  Have you never used a Chronometric speedometer?

Offline sparx

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Re: Jerky Speedo?
« Reply #6 on: 08.08. 2015 13:59 »
Oops. I was thinking magnetic. My apologies  *red*
Dave
Peterborough (UK)

Offline AndyDenmark

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Re: Jerky Speedo?
« Reply #7 on: 08.08. 2015 14:13 »
Thanks for the replies I will keep an eye on it but it does seem to be extremely jumpy *smile*

Online Triton Thrasher

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Re: Jerky Speedo?
« Reply #8 on: 08.08. 2015 14:29 »
My apologies  *red*

That's going a bit far!

Online chaterlea25

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Re: Jerky Speedo?
« Reply #9 on: 08.08. 2015 19:58 »
Hi,
Have a look at these and compare,  then tell us how your speedo compares?
The one of the RE is what you should expect , lousy video though

https://www.youtube.com/watch?v=6dknqvZBfpk

https://www.youtube.com/watch?v=DQezLyGxLvM

https://www.youtube.com/watch?v=RYEUBy0N5rY

HTH
John
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Re: Jerky Speedo?
« Reply #10 on: 10.08. 2015 00:49 »
extremely jerky? no shouldn't be.
jerky... depends on your definition.
these are a counting instrument much like a clock, so do step up and down in small increments.
Over tight cable ends or bad cable runs can effect this .
Its not uncommon for them not to return to 0, In practice they are usually a good instrument to read.
Do you have a tach or just the one instrument as it can be useful to swap in another comparative instrument.
I've found over the years that my B33 in particular is very susceptible to over tightening the cable at the gearbox end and in I have the cable fairly lightly done up it is much smoother.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline AndyDenmark

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Re: Jerky Speedo?
« Reply #11 on: 12.08. 2015 09:33 »
Having looked at the videos and comments mine does not return to zero and appears to be on the top end of the " jerkiness" scale so I will have a look at the connections...many thanks for the inputs.

Offline duTch

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Re: Jerky Speedo?
« Reply #12 on: 12.08. 2015 14:33 »

 
Quote
top end of the " jerkiness" scale

 aka "Jerkometer...  *conf*
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Offline Viking

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Re: Jerky Speedo?
« Reply #13 on: 19.08. 2015 09:21 »
Good news for you.

You can get a new digital “chronometric instrument” from Smith http://www.smithsinstruments.co.uk/bike.html

http://www.puca.co/productC.html

You can choose in the setting: smooth of jump

Smooth = Modern instruments
Jump = Chronometric instruments.

For an odometer, jumping is ok, works well, but for a rev. counter, the jumping is a “pain”
It can never catch up with fast changing engine rpm.

If your instrument jumps too much, it need service. Send it to at UK specialist and get it rebuild.