A bit OT - Tachometers

I need an electronic tachometer to run with a 4 cylinder engine that uses a magneto rather than coil ignition. I'm told that a standard
electronic car tacho won't work. The one that I have gathering dust works off the main coil HT lead anyway (which a magneto engine doesn't have)
There must be a solution but it's eluded me - quite a lot does. Any of you knowledgable types know where to find one?
Thanks
Charles
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Charles Ping wrote:

Inductive pickup works. Depends on the trigger voltage requited to the tacho though.
Have done this with wire wrapped around one of the HT leads.
I think the Vellemann digital tacho available as a kit from Maplins will work with a low enough trigger voltage.
Wayne...
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On Fri, 03 Nov 2006 16:10:17 +0000, Charles Ping

    Could you not mount a 'sensor' (proper term alludes me) on the flywheel a la modern machine tachos? Are we talking about pre'28 Austin Seven engines? Where's Tony Jeffree when he's needed! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Chris Edwards wrote:

You know me too well Chris. Because it's for an old car it needs to be disguisable in an original analogue type casing.
Charles
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wrote:

Rules out my digital tacho then ;-)
Regards, Tony
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wrote:

    Crank 'Tachometer' into the e-Bay search box, there are a couple of items buried in the hundred or so hits that you might be able to adapt. I think you need a ' non-contact' type of sensor. Have a look at Items 150052944157 and 190047192212. Perhaps one of these might be adapted? A --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
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Get a standard Lucas tacho off a 1960's - 70's vehicle, of the sort that uses a turn of wire wrapped round a post on the back of the instrument, and wire the loop in series with a load resistor and inductive proximity sensor suitably and subtly placed to avoid sight.
AWEM
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On Fri, 3 Nov 2006 19:29:22 -0000, "Andrew Mawson"

Andrew
Thanks for the tip. However as you know cars of the 60's and 70's are a bit modern for me. Come to think of it hydraulic brakes are way ahead of my garage. Would you care to point me at a model or spec that would suit. I've scouted through Ebay and can't see one that matches your description of the "wire wrapped round a post".
Ta
Charles
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On Fri, 03 Nov 2006 23:00:44 +0000, Charles Ping

My fork truck would gladly appreciate at least one brake.
. -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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John Stevenson wrote:

John, you haven't lost the brakes again!, after you loaded the mill I definitely left them propped against the wall. Perhaps someone has borrowed them for their bonfire or have you been throwing them at next door's cat again?
Regards
Keith
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that
standard
lead
sight.
me.
Charles,
The one used on my Austin Healey 3000, and was used from about 1960 onwards, has a plastic block with a hole in it held on with a screw on the rear, and the block is encircled with a steel strap. This strap forms the laminations of a transformer whose primary is a loop passed through the hole in series with the ignition coil primary, and whose secondary drives the pulse averaging circuitry. Same basic tacho used on MG's and Triumphs - here is an article about them:
http://www.mgexperience.net/article/tachometer.html
This chap is very good on repairing / calibrating Lucas instruments and maybe can supply:
http://www.jdo1.com/index.html
Good luck,
Andrew
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I made one of these a few years back for a boat - it worked straight off, but suffered from a lack of high voltage components - I'll scan the schematic for you if you are interested, pretty simple.
Steve
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On or around Fri, 03 Nov 2006 16:10:17 +0000, Charles Ping

some of the modern ones work from a tapping on the AC on the alternator. They're not particularly accurate though.
--
Austin Shackles. www.ddol-las.net my opinions are just that
Satisfying: Satisfy your inner child by eating ten tubes of Smarties
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On Fri, 03 Nov 2006 16:10:17 +0000, Charles Ping

I don't know whether you have solved your problem, but if not try www.scitsu.com
They are located in Sheffield, phone number on web site. They make tachos for racing bikes, 2 stroke or 4 stroke. Pick up from HT lead. Phone them and I am sure they will have one to suit you, but they aren't cheap.
-- brightside S9
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