Author Topic: Electronic tacho  (Read 972 times)

Offline yar

  • Moving Up
  • **
  • Join Date: Nov 2012
  • Posts: 10
  • Karma: 0
  • coming soon
Electronic tacho
« on: 02.08. 2017 04:42 »
  HI all
I am interested in fitting A Speedhut legacy tacho to my 59 super rocket. These from the makers say they can be fitted to Most gasoline engines and do not require a sender, and can hook up to a coil
However can they pick up the signal from the HT lead on the twin , they do say not to splice onto the HT lead as will damage the tacho. But I have seen reference on cheaper tachos that you can wrap a signal /pulse wire around a HT lead to get a reasonably accurate signal to the tacho,
Anybody done this ?, if so what brand was used and how did it work? The Speedhut tacho is small enough to possibly fit in a Smith case, and can have the Bezel screwed off to remove needle and overlay with a matching dial. :)Yes I know its not original but I have the wrong oil pump and don't have the correct tacho which I believe is a reverse 3/1 I also don't want to run a cable off the magneto, as I will have to drill through cover and tap ,plus change mag drive etc
I would appreciate any info from anybody that has had a go at fitting any electronic tacho to there magneto bikes
thanks Ray
Bike Tragic

Online Triton Thrasher

  • Scotland
  • Wise & Enlightened
  • *
  • Join Date: Feb 2009
  • Posts: 1475
  • Karma: 20
Re: Electronic tacho
« Reply #1 on: 02.08. 2017 06:38 »
This sort of six quid thing works on my magneto.  You have to mess around trying different numbers of turns on the HT lead and maybe trying the other HT lead, to stop it reading double your rpm.

http://www.ebay.co.uk/itm/Spark-Plug-Engine-Digital-Tach-Hour-Meter-Tachometer-Gauge-High-Quality-/142145169243?hash=item211883275b:g:lOgAAOSw8w1X~IVk

There's also the more expensive Scitsu, which is more like the right shape.  Possibly more temperamental too.

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Electronic tacho
« Reply #2 on: 02.08. 2017 11:23 »
 The good thing about TT's unit is that it 'may' be ok with 'some' A10's; *smile*
Quote
Reading: 9999.9Hrs / 99999RPMs /quote]

 
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Topdad

  • bob hebdon
  • Wise & Enlightened
  • *
  • Join Date: May 2011
  • Posts: 2222
  • Karma: 32
  • l
Re: Electronic tacho
« Reply #3 on: 02.08. 2017 14:23 »
I tracked down a company in Belgum who were offering a tacho using the same system at a reasonable price. I think they could fit it in a smiths case which you could buy on the net . Lost that PC and the info sorry can't help further than that .
" rules are made for the guidance of wise men and the blind obediance of fools"
United Kingdom

Online Triton Thrasher

  • Scotland
  • Wise & Enlightened
  • *
  • Join Date: Feb 2009
  • Posts: 1475
  • Karma: 20
Re: Electronic tacho
« Reply #4 on: 02.08. 2017 17:43 »
The good thing about TT's unit is that it 'may' be ok with 'some' A10's; *smile*
Reading: 9999.9Hrs / 99999RPMs

Well you want a fast engine that lasts, don't you?
The handbook says "Keep the engine spinning freely."

Online BSA_54A10

  • Wise & Enlightened
  • *
  • Join Date: May 2008
  • Posts: 1940
  • Karma: 32
    • BSA National
Re: Electronic tacho
« Reply #5 on: 04.08. 2017 09:27 »
Tiny tach.
Buy them from a mower shop $ 45
They will also tell you how many hours the engine has for as well
Bike Beesa
Trevor

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Electronic tacho
« Reply #6 on: 04.08. 2017 10:33 »

 
I tracked down a company in Belgum .........

 good ol' Belgum *smile*

 anyways, i went beresk and bought two of these; one for test purpose, and one to jam in the red truck because it tacho-no-go
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline coater87

  • Wise & Enlightened
  • *
  • Join Date: Jul 2008
  • Posts: 1181
  • Karma: 6
Re: Electronic tacho
« Reply #7 on: 04.08. 2017 14:03 »
 There are a lot of "ifs" with this.

 Wrapping wire around the HT lead, your basically building a very crude transformer. A small voltage will be pumped into your wire wrap which the electronic tach can sense. When this voltage is sensed the electronics are counting pulses, it does some math and you get a RPM read out.

 Without making this over complicated, the method of wrapping wire around a HT lead makes a very muddy signal. Its not a clean and crisp OFF ON OFF ON OFF ON. Its more like a light someone is showing you thats going off and on so fast that its never really off (if that makes sense).

 So your electronics have to be good enough to differentiate between OFF and ON. Even with pretty expensive stuff thats not always easy. If you are getting a reading, it may not be all that accurate all the time, because the electronics are having to do some guessing.

 Lee

 

 

Central Wisconsin in the U.S.

Offline yar

  • Moving Up
  • **
  • Join Date: Nov 2012
  • Posts: 10
  • Karma: 0
  • coming soon
Re: Electronic tacho
« Reply #8 on: 05.08. 2017 03:26 »
Thanks  Lee for your input . im beginning to realise that other sources of electrical equipment will interfere with a signal picked up this way. As the bike is a magneto ignition and at the moment just an external  charged battery being used for stop light use,( I don,t ride the bike at night) do you think there would be a lot of interference to the signal or perhaps using  a sensor pick up signal attached to lead or is it possible to pick up from the mag itself be better ? I believe an HT sensor is made by Smiths that might be better than just wrapping around the spark  plug lead
 cheers  Ray
Bike Tragic

Offline coater87

  • Wise & Enlightened
  • *
  • Join Date: Jul 2008
  • Posts: 1181
  • Karma: 6
Re: Electronic tacho
« Reply #9 on: 05.08. 2017 13:46 »
 Hi Ray,

 If smith's makes makes some dedicated electronics for doing this, I would spend the money and try that. Someone (else *smile*) has already put the time into making this thing work, or at least work as good as it can.

 I am not trying to say I know for sure wire wrapping wont work, I am saying its not the best way to receive a clean signal if you want a pretty accurate tachometer.

 Lee
Central Wisconsin in the U.S.

Offline Viking

  • A's Best Friend
  • ***
  • Join Date: May 2015
  • Posts: 127
  • Karma: 2
Re: Electronic tacho
« Reply #10 on: 04.09. 2017 20:52 »
Fit a sender unit in the SR tacho drive and get the Smiths instrument.

Works well..

Online bsa-bill

  • Wise & Enlightened
  • *
  • Join Date: Mar 2006
  • Posts: 5379
  • Karma: 61
Re: Electronic tacho
« Reply #11 on: 04.09. 2017 21:43 »
Quote
Wrapping wire around the HT lead, your basically building a very crude transformer. A small voltage will be pumped into your wire wrap which the electronic tach can sense. When this voltage is sensed the electronics are counting pulses, it does some math and you get a RPM read out.

Just to muddy the waters a bit and thinking aloud
I have an electronic speedo that I haven't got around to using yet, can't recall if I have the pickup as well (damn memory again)
I have electronic ignition, so have a spark twice as often as often, wonder if there's a way around this?. maybe get a pulse off the ignition unit.
Never mind this is for the future
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline Greybeard

  • Jack of all trades; master of none.
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 5851
  • Karma: 32
Re: Electronic tacho
« Reply #12 on: 04.09. 2017 23:05 »
...I have electronic ignition, so have a spark twice as often as often...
As the Irishman said; "To be sure to be sure".

Online mikeb

  • Resident Legend
  • *****
  • Join Date: Dec 2014
  • Posts: 512
  • Karma: 10
Re: Electronic tacho
« Reply #13 on: 05.09. 2017 07:52 »
Quote
get the Smiths instrument
they need 12v so not for 6v bikes. otherwise look great
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Offline Slippery Sam

  • A's Best Friend
  • ***
  • Join Date: Aug 2016
  • Posts: 120
  • Karma: 1
Re: Electronic tacho
« Reply #14 on: 06.09. 2017 20:07 »
I have a feeling this has been discussed before?
But - my experience, albeit limited - was with a supermoto bike, with no battery and no tacho wires or sensors.
I needed to set the tickover so bought a very cheap Chinese digital tacho with a wire to wrap round the HT.  It worked perfectly and althovugh I didn't calibrate it - it appeared to be spot on and worked exactly as described with no issues whatsoever.
I'm sure it's in the bottom of a drawer somewhere so if I come across it I'll dig it out.  Pretty sure there was a switch or setting for number of cylinders/sparks?  My supermoto was a single so can't be sure.
Other than Bills double spark - will an HT not normally just fire once per 2 cycles? Regardless of number of cylinders?
Would be dead easy to calibrate on a vehicle with a tacho.
Also on the note of accuracy - in comparison to a chronometric any rough approximation would be better😀😀😀
Cheers Raymond
BSA A10 Cafe Racer project
Scotland