Speedwell Weston Rev counter and 123 ignition distributor

[almondgreen]

I have problems with my Weston Speedwell rev counter.
It does not work in my Mini.
I have fitted a 123 ignition distributor that works fine.
The Smiths rev counter is running too.

I have tested the Weston instrument in a standard Mini with points and it works.

Any suggestions, where the problem is ?

(I fitted a new coil too)

[Astro]

http://mk1-performance-conversions.co.u ... ho_ins.jpg

have you seen this?

[almondgreen]

yes, it runs with a standard dizzy with points.

[mk1]

A Weston usually runs with whatever set up you have. The Smiths made Speedwell (induction loop) Gauges are the sensitive ones.

I have never used a 123 dizzy, so cannot suggest what the problem may be.

maybe best to contact the manufacturers.

[Jack of all trades]

Hi,

Most of the "old" tachometers are current driven, when you fit "electronic contact breakers" the current isn't enough anymore to drive the tacho. That's why you end up with more spark!
The thing to do is convert your tacho from current to frequency driven.
You can do it yourselve (if you have the skills) like this way;
http://www.dinoplex.org/tachoconversion/
Or buy an "add on box" like this;
https://www.spiyda.com/magento/index.ph ... board.html

[mk1]

Those are a couple of cracking links Jack.

I'll add them to the Recommended sites page.

I'm not certain that they would help the problem with the Speedwell Weston as these are as I understand it Frequency driven as is.

[Jack of all trades]

Mark,

As i look thrue the data of the Weston on the main site;
http://mk1-performance-conversions.co.u ... ston_1.jpg
it states "current to operate the meter etc." so this one is current driven aswell, the frequency driven ones came around in the late 60's early 70's

As the electronic "points" are on/off type the current driven is so very low the old Rev counters just can't detect it anymore.

I've rebuild several Smiths counters (the dinoplex way, made my own circuitboard) for use with Aldon ignitor contact breakers and they are more accurate and generally work better then when new!

[mk1]

Thanks for clearing that up Jack.

[almondgreen]

Thank You for all the input.
I know the way to go now.
But I think my electrical skills are not enough for this.

[swifty]

Maybe speedy cables have come across this problem and may be able to help ? . Worth a call . ... Ken

[mk1]

Personally I wouldn't be trying to bugger about with the innards of a Speedwell Weston. These are around £350 & up nowadays & are completely potted from new. To muck about with the innards you would need to destroy what is there to begin with. A mucked about (all be it working with modern ignition) Speedwell Weston is NEVER going to be as valuable as a totally original one that will only work in an original set up.

[dklawson]

I fully agree with Mark. While it is your gauge to do with what you wish, altering it will diminish its value.

[almondgreen]

I do not want to destroy the rev counter.
I am still hoping for a solution that simulates the signal the rev counter needs.

[Spider]

Sorry, I'm not clear on this, is this a current driven tacho, ie one where a coil wire passes through the tacho? Similar to the Smiths RVI type, like this?

[almondgreen]

I have been just told to try this:

"put a diode in the line between the coil and the tacho"

What do You think of this, can this work ?

[Astro]

A diode let electrons pass just in one direction. It's not expencive and will not destroy anything. Why not.

[dklawson]

Spider. Yes, that is an impulse tach. If it is not Smiths, it is similar. Current flowing through the coil also flows through that loop of white wire on the back of the tach and induces a pulse inside the tach which is then measured/processed. Later impulse tachs put the loop of wire completely inside the gauge case. Later impulse tachs can be identified by the presence of a pair of male and female bullet connectors on the back instead of the loop of white wire.

Almondgreen. There have been many suggestions made over the years to make impulse tachs work with electronic ignitions. None (or almost none) of the suggestions out there were posted without someone, somewhere, having success with them. However, in general they don't work for most gauges. In addition to the diode you will also find some recommendations to try various capacitors. Try them. You may find one of them works and they don't cost much to try. However....

The issue is that the dwell of the ignition system is different for operation with points than it is for electronic ignitions. The impulse tach was designed in the era of points and it is expecting the current to be flowing for a certain percentage of time. Adding diodes or capacitors to the circuit to change the duration of the current pulse seen by the tach may bring it back into operation. However, those changes also alter the behavior of the electronic ignition system. (i.e. Electronic ignitions don't use condensers. Adding a capacitor to the tach circuit to make it work is like adding the condenser back to the ignition system. You will be changing the ignition system to be have more like points).

I am hesitant to suggest the following for a period, collectible instrument but you could consider modifying it (reversibly) using one of the instrument packages offered by Spiyda Design (Chris on this board posted info within the past month). They make a conversion box that can be mounted remotely. You could open your tachometer, disconnect its red/black wires from the movement, connect the remote tachometer electronics to the movement, and mount that conversion box remotely... out of sight. That way the old movement would still be present and the alteration would be reversible. This of course assumes the bezel on your tach is easily removed so the movement can be worked on. If not... please completely ignore this last paragraph!
https://www.spiyda.com/magento/index.ph ... board.html

[mk1]

The vast majority of Speedwell Westons are potted in a solid lump of gloop & none of the gubbins can be accessed.

[almondgreen]

My Tacho is easy to Open
It should ne no Problem to change the red and
Black wires

[mk1]

Good luck Andreas, let us know how it goes.