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Smiths revcounter
dutchsuperseven - 22/12/04 at 07:37 AM

Is it possible to change a Smiths 4cyl rev-counter in such a way that i can use it with a 6-cyl engine?

Greetings Rob

zetec - 22/12/04 at 08:12 AM

I think Speedy Cables/greenguages can do it. They restore guages, fit new workings to old guages etc. I'm sure the guage will work but read 50% high (I think!).

dutchsuperseven - 22/12/04 at 08:42 AM

It will surely work. but there must be some way of modifying it on a d.i.y. basis?
Maybe change a resistor in the internals?

Greetings, Rob

Mave - 22/12/04 at 04:16 PM

Rob, since when is a Zetec a 6-cylinder engine?

(helping out Jack I pressume?)

Marcel

dutchsuperseven - 22/12/04 at 08:47 PM

Its all part of the special operations programm, Mave
Still top secret!
Greetings, 00super7

MikeRJ - 22/12/04 at 09:46 PM

quote:
Originally posted by dutchsuperseven
It will surely work. but there must be some way of modifying it on a d.i.y. basis?
Maybe change a resistor in the internals?

Greetings, Rob


Rob,

That is exactly what you have to do. The frequency/voltage converter circuit relies on an RC network, changing either the R or the C will change calibration. I have converted a couple of 6 cylinder ones to 4 cylinder in the very distant past, and it wasn't hard.

If initial inspection of the circuit does not obviously show which are the timing components, you can simply connect the tachometer to the engine, and whilst running use a lowish value, non-electrolytic capacitor (say around 0.1uF) and touch it accross any likely looking capacitors. When you see the needle move you've likely found it.

The reading will be 50% too high with a 6 cylinder engine, so you'd need to increase the value of this cap by 50%, or increase the value of the ascociated resistor by 50% (will probably be connected to this cap at one end). The gauges I modified had a trim pot for calibration IIRC, so I upped the value of the resistor and then fine tuned the calibration with this pot, using a signal generator and frequency counter.

[Edited on 22/12/04 by MikeRJ]

dutchsuperseven - 23/12/04 at 08:12 AM

Mike,
Can i use this method to change the rev-counter from a 4-cyl into a 6-cyl rev-counter?

Greetings, Rob

MikeRJ - 23/12/04 at 04:09 PM

quote:
Originally posted by dutchsuperseven
Mike,
Can i use this method to change the rev-counter from a 4-cyl into a 6-cyl rev-counter?

Greetings, Rob


Yes, you should be able to modify it for any reasonable number of cylinders.

David Jenkins - 23/12/04 at 07:29 PM

Rob,

A dumb question... this isn't a modern Smiths tacho is it? If so, there's a rubber bung in the back with a DIL switch underneath. If you have one of those let me know - I can give you the correct switch positions for 4, 6 or 8 cylinders.

If it isn't a modern tacho - ignore me!

David

dutchsuperseven - 24/12/04 at 07:36 AM

Unfortunately it's one of those middle-aged rev-counters from the mid-70's.

Best wishes, Rob