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Replacement Speedometer Drive.
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_Paul_
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November 5, 2018 - 3:39 am
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Something else has failed on my old D14 the speedo drive has given up looks like the big gear in the middle has stripped its teeth.

Not many of these things around on eBay and the ones there all seem to be 2:1 ratio which is wrong for 18" wheels it should be 19:10.

I can get a 2:1 drive but my question is how far will it throw the speedo out? anyone using a 2:1 unit?

Regards

 

Paul

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johnsullivan
east sussex
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November 5, 2018 - 8:09 am
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Not much the tyre choice can have as much effect.in theory you will be ten percent out .I have an app on my phone called HUD which has proved very handy for recalibrating the Stag which has oversize tyres.A dot of tippex at true 30 on the glass keeps one legal.the Stag of course has a rev counter as cross check.I also have one of the optical rev counters where you stick a bit of reflective tape to the rotating part and the lazer gives you the speed Best thing ever for confirming lathe speed with dodgy domestic voltages.On the Montesa I have a bicycle speedo on the front.a stronger magnet on the rim ..works very welll indeed.

67 D10. and a D7    2007 Honda Hornet FA. Suzuki 89  DR 250S, Sinnis SC 125. 78 Honda 90  75 Montesa Cota 247

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SpacedMarine
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November 5, 2018 - 11:10 am
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Wouldn't even be that as 1/20 is 5% and as you say tyre choice could affect it anyway.

What's 7/16 in mm again?

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Peterg
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November 5, 2018 - 11:20 am
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With the new gear box the speedo will read 5% slower as the rear wheel has to turn two times instead of 1.9 times to turn the speedo cable once

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johnsullivan
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November 5, 2018 - 12:28 pm
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I was factoring the as new error...myfanwy can travel at a good fraction of the speed of light if the cable is nice and clean..

67 D10. and a D7    2007 Honda Hornet FA. Suzuki 89  DR 250S, Sinnis SC 125. 78 Honda 90  75 Montesa Cota 247

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_Paul_
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November 5, 2018 - 3:35 pm
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Thanks guys,

Ordered a 2:1 ** Please log in to view ** which has a 16mm (5/8") centre hole unfortunately the gubbins is the wrong way round, but I did read on the BSA forums that it is possible to swap the ends over, so will pull it apart and at the same time recut the metric threads to imperial.

Found an app called "DigiHUD" is that the one you use John?  

Regards

 

Paul

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mike p5xbx
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November 5, 2018 - 3:52 pm
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is it not the other way around
1 turn wheel = 1.9/2.0 turns cable
or is SD getting to me frown

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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_Paul_
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November 5, 2018 - 4:54 pm
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mike p5xbx said
is it not the other way around
1 turn wheel = 1.9/2.0 turns cable
or is SD getting to me frown  

The big helical driving gear has 19 "teeth" the smaller driven one 10 so one turn of the driver produces 1.9 turns of the small helically cut gear.

it looks like you're good with the SD Mike 😀

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johnsullivan
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November 5, 2018 - 5:11 pm
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Yes good fun when you are walking too.

67 D10. and a D7    2007 Honda Hornet FA. Suzuki 89  DR 250S, Sinnis SC 125. 78 Honda 90  75 Montesa Cota 247

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mike p5xbx
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November 5, 2018 - 5:47 pm
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_Paul_ said
it looks like you're good with the SD Mike 😀  

oh good now if I could only remember where I put my glasses
and why I keep walking upstairs but cant remember why

does it really matter if the output is at the top or bottom of the axle ?
and I think the speedo drive thread is the same as used by smiths,
I have an Indian Enfield speedo and cable on my D14 which fits the original drive gear

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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_Paul_
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November 5, 2018 - 9:23 pm
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mike p5xbx said

oh good now if I could only remember where I put my glasses
and why I keep walking upstairs but cant remember why

does it really matter if the output is at the top or bottom of the axle ?
and I think the speedo drive thread is the same as used by smiths,
I have an Indian Enfield speedo and cable on my D14 which fits the original drive gear  

Ditto with the glasses!

Top or bottom? as long as it spins the cable I don't really mind just need a working Speedo, if it comes apart readily then I will turn it about.

The threads should be very similar, the original Smith's unit I just measured at 1/2" X 26 tpi (cycle thread) the new unit is allegedly 12mm X 1.0mm so the thread pitch at 1.0mm = 25.4 tpi which on such a short thread will barely be noticeable, the diameter is 12mm = 0.472" so may not have quite enough purchase.

Regards

Paul

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