31 replies to this topic

[dklawson]

RVC = newer = points or electronic ignition = voltage pulse sensing = parallel wired

RVI = older = points ignition = current pulse sensing = series wired

[Dusky]

Working now ( engine runs yay)

But reads around 1K rpm bu tby sound of the engine it is way higher. Probably needs calibrating but any ideas on how to do that?

[dklawson]

You will probably need to borrow another tach (even if it is just a tune-up tach) to confirm the accuracy of your gauge.

 

I found the old thread linked below which confirms the wiring:

http://www.theminifo...counter-wiring/

 

Note the picture in that thread shows the same model tach as yours (from what detail I can read from the picture of your gauge's face it looks like you also have a 1003/00F).  However, the tach in the other thread as a cylinder selector on the back that yours does not appear to have.  Maybe it is inside?  If there were an cylinder selector and it were set to 8 instead of 4, your tach would be reading 1/2 the real engine speed.

 

Some early RVC tachs had trim pots on their circuit boards that would allow calibration.  Later ones did not.  They were what they were where the only minor calibration possible was adjusting the tension of the hairspring that returned the needle to zero when the engine was not running.

 

Regardless, I don't know how easy it is go get inside of this style of tach to work with its calibration.  The OEM tachs as the factory used in MGs were easy to take apart to access the electronics.  I think the aftermarket type like you have is harder to open if it can be opened at all.

 

EDIT:  Dusky, going back and looking at your pictures again... the photograph of the gauge face you posted... is it YOUR gauge or is that a catalog or otherwise generic photograph?  I'm not picking or anything, but it looks like a professional photograph and may not represent your exact gauge.  If the photograph is just one that looks like your gauge, that's fine.  But look at the numbers on the bottom of the dial for your gauge and tell us what they are.  It should say something like "RVC 1XXX/YYY"  where the Xs and Ys are replaced by numbers and letters.

Edited by dklawson, 13 February 2014 - 11:08 PM.

[Dusky]

Not my tach indeed but looks exactly the same..
My tach comes of my dads race mini with electronic ignition,was removed.for a.digital counter.with limiter...
Thats why I guess I need callibration:p

[Dusky]

will look tonight for numbers(im at school atm:p)

[Dusky]

Here are the pics : 

 

Doesn't have a 4-8 cylinder switch I guess...

But really wont go higher than 1500 rpm, still revving the mini above 4K I think... Could this be due to wiring orso?

 

 

grtz

[Dusky]

could it be bad wiring? had to put the 'trigger wire' on the + of the coil to make it move..

[dklawson]

The tach should not have worked at all by moving the trigger wire to coil (+). 

 

Modern tachs (and yes... Smiths RVI tachs are still considered modern) work by sensing voltage pulses.  On a negative earth car, there is very little change in the voltage on coil (+) as the points open and close.  The coil (-) terminal is used because its voltage switches between 0V and 12V each time the points open and close.

 

My advice is two-fold.  

1) Remove the tach from your car and with some short wires, connect it to a friend's car... something with a simple points ignition system.  V+ to the battery positive terminal, V- to the battery negative terminal, Trigger to their car's coil (-) terminal.  See if the tach reads properly.

2) On your car, test the tach by removing (temporarily) any wiring that is on the coil that is not required.  I don't remember which type of ignition your car has (standard or ballast).  A basic "standard" ignition will have minimum requirements of a white wire from the ignition switch on coil (+) and a white/black wire between coil (-) and the distributor.  Make your wiring that simple.  You said your tach is getting power from the starter solenoid and that you have provided an earth connection.  Double check the earth connection and make sure you measure 12V at the tach when the engine is running.  Make sure the trigger wire has a good clean connection to coil (-).  Also, even though it may not say it is required, make sure the tach case has a good earth connection.

 

If the tach does not work on a friend's car you know it needs repair.  If it works properly on a friend's car you will know that the gauge is operational and the connections in your car are somehow not right.

[Dusky]

Okays,will try that.
I have a normal non ballast coil, just wondering if it will change anything if I would turn the coil 180 degrees? engine wont run then I guess? its weard it runs with the triffer on +.. any harm if i switch + and - earths?

[dklawson]

Do you mean switch the coil polarity (power in on coil (-), distributor connected to coil (+))?  If that is what you mean, the results are pretty well documented.  A coil will work with reverse polarity but will have lower output voltage.  It's an electro-physics thing that I am not comfortable trying to explain.  Maybe Tiger will post to this thread and explain it.

 

Regardless, switching the coil polarity will in no way change the way your tach is working.  The tach is connected to the low-tension circuit and what it is looking for is a voltage swing between 0V and 12V.  That will still happen when the points open and close regardless of which coil low tension terminal are connected where.

[Dusky]

and the - and + on the gauge itself? or would it stop working?

[dklawson]

I don't understand your question.

[Dusky]

connecting the -VE to the starter and.the +VE to the body?

[dklawson]

Connecting the power that way sounds like a sure way to let the white smoke out of the parts inside.

[Dusky]

Hmm, won't do it then I thought maybe because he works on the + side of the coil..