Dash board gauges

[Marlindan1965]

Hi

I have a couple things about gauges the first one might help someone else the second is a question of my own.

1. My temp gauge has been over-reading for sometime. I have looked at various posts on the forum and there was a lot of talk about sender options compatible with gauges etc. I have a smiths gauge that has N at one end H at the other and N in the middle. I found a semi conductor voltage stabalizer on ebay that said it was the modern equivalent of the units that used to be used with smiths gauges. It also said that it always sends a 10v supply to the gauge and this means it is very accurate. At £12 it was more than a direct replacement for the unit I did have. That said I had a go and it has really done the trick. My gauge was always reading near H even when I had not been in the car long enough for the car to warm up never mind overheat! I know the cooling is good on the car (Triumph Vitesse based) as I have been stuck on the motorway crawling in mid summer and had no problems with boiling despite the gauge telling me otherwise. So I would recommend this unit as it is great and it is always reassuring when you have faith in your gauge readings.

Right on to my problem.

2. My rev counter is under-reading! It is a Smiths RVI unit for 6 cylinder negative earth. I converted the car to electronic ignition back along and at the same time my brother in law gave me an old RVI rev counter, it was not in a good way. So I sent it off to Speedograph Richfield to be overhauled and converted to be compatible with an electronic ignition. They weren't great to deal with and had the unit for ages! Anyway eventually got it back and a mate of mine who is much better at electrics than me wired it up as per instructions. It worked great on tick over so I left. Now I get to the problem. It progressively under-reads as the revs increase and the unit never goes above about 2 1/2 thousand revs. I know that when the car is at about full tilt the engine is at about 4 thousand revs.

I have done a bit of research on this and talked to some people and they say that it isn't picking up the pulses from the coil as they get faster. The question is how do I make it work accurately. I have also read that a balast resistor is used in some systems (haven't gone one on mine) for the purpose of making the gauge read more accurately. I have also read that you souldn't use them with electronic ignition. I am very confused and rambling!

Does anyone have any suggestions about making the gauge read accurately. After my experience with Speedograph Richfield I decided there was no way I was going to send it back to them (assuming it is there fault). I can live with it but think that if you have gauges in a car it's great if they work!

Hope to hear from someone (I bet Ben gets back to me with the answer)

Regards

Dan Cook

[philcoyle]

Re: Dash board gauges

Have you checked that the rev counter wire from the coil is not on the feed wire to the coil, the green wire must be connected to the -neg side of the coil.

[b_caswell]

Re: Dash board gauges

Hi Dan, I think your confidence may be premature but along with Phil's suggestion here are a few other points..... I) Check that you do have 12V at the coil a the ballast resistor can be the wire that feeds the coil (not obvious and even so I don't think a 6V coil feed will make any difference....2) Ensure the Tacho itself is properly earthed......3).Ensure the supply feed to the Tacho is taken from a 12V feed and not from the 10V side of the stabilizer. 4) Try borrowing a substitute Tacho to see what happens. Alternative is to convert to a cable drive Tacho I know how that works.

[Mike]

Re: Dash board gauges

Hi


My temp gauge has been over-reading for sometime. I have looked at various posts on the forum and there was a lot of talk about sender options compatible with gauges etc. I have a smiths gauge that has N at one end H at the other and N in the middle. I found a semi conductor voltage stabalizer on ebay that said it was the modern equivalent of the units that used to be used with smiths gauges. It also said that it always sends a 10v supply to the gauge and this means it is very accurate. At £12 it was more than a direct replacement for the unit I did have. That said I had a go and it has really done the trick. My gauge was always reading near H even when I had not been in the car long enough for the car to warm up never mind overheat! I know the cooling is good on the car (Triumph Vitesse based) as I have been stuck on the motorway crawling in mid summer and had no problems with boiling despite the gauge telling me otherwise. So I would recommend this unit as it is great and it is always reassuring when you have faith in your gauge readings.

Hi Dan.
I had a similar problem with my new Smiths Classic water temp guage significantly over reading - boiling point was over 140 degrees C! Turned out to be my own fault as I had wired it to a 12v supply. A friend pointed out it needs a 10v supply!

Maplin sell a modern printed circuit board 10v regulator for £1.04 each - part number N38CA.
It has 3 pins: 12v +ve input, Earth, 10v +ve output.



Mike

[stevejgreen]

Re: Dash board gauges

Ballast resistors were not on the original Mk1 Marinas, only fitted on the later MK2 Export (LHD) models, according to some info I have. Triumphs are probably very different.
Tacho should be 12V feed from ignition switch and the signal wire comes from between the coil and distributor.

[b_caswell]

Re: Dash board gauges

Dans car is a Triumph based car and if it used a later wiring loom the ballast resistor was incorporated into the loom and usually coloured pink with a white tracer. My sons car uses the ballast resistor and has an electronic Tacho albeit on a four. That works OK If the supply to the coil is ballasted and the live feed to the tacho was taken from there that may explain the low reading.

[neiltechspec]

Re: Dash board gauges

Simple answer is to find a similar styled RVC tacho and have it re-calibrated to 6cyl if needed. RVC's are much simpler to connect and not fussy about ignition types - points or electronic.

Many years ago (25 maybe) on my Triumph 4cyl, I swapped the face and needle from a 4cyl RVI onto 6 cyl RVC innards, from a Scimitar, then re-calibrated it myself.
Some specialist kit is needed really for that, which I have - a pulse generator, freq counter and electronics knowledge. From what I can remember it was only a resistor value change (reduced in value).

Neil

[b_caswell]

Re: Dash board gauges

Neil, How do you tell the difference between a RVI and a RVC tacho. I may have a spare but I don't know which it is.

[Tnick]

Re: Dash board gauges

Hi Ben

There are two type of electronic tacho

Current sensing tachometers were used on many British cars through the 1960s. Inside the tachometer are electrical components including electrolytic capacitors which were not designed to last 30 or 40 years. As these older components fail they can be replaced to restore operation but again, this profe ssional repair may not be cost effective. In addition, there is a trend to replace traditional points ignition systems with aftermarket electronic ignitions. For reasons beyond the scope of this document it is often the case that the current sensing tachometers will not work with electronic ignitions. The Smiths tachometers falling into this category can be identified by the letters RVI appearing on the gauge face.

Voltage sensing tachometers were used on most cars after the 1960s. Like the current sensing tachometers, inside are
electrical components which were not designed to last 30 or more years. As these older components fail they can be replaced to restore operation but again, this professional repair may not be cost effective. The Smiths tachometers falling into this category can be identified by the letters RVC appearing on the gauge face

For more info and suggestions on repair / upgrade see

http://www.gomog.com/allmorgan/smiths_tachometer_conversion.pdf

Regards

Nick

[neiltechspec]

Re: Dash board gauges

The post above tell you how to spot the difference, just look for RVI or RVC on the tacho face.

Not sure about the repair aspect being that simple though, the older RVI gauges used what they call "Germanium" semiconductors, everything is silicon based nowadays and not directly interchangeable.

Swapping the innards as described in that link above is definitely the way to go, but not for the inexperienced.

Neil.

[nigel]

Re: Dash board gauges

Just had a similar problem on my Sportster with a Smiths Telemetrix rev counter. It was reading a bit high on tick over and progressively too high as the revs increased.

But a simple flick of a couple of dip switches in the back of the tacho calibrated it for a 6 cyl engine instead of a 4 it was set for and now its fine.

I've always thought that car electrics had become a lot more complicated over the years, but sometimes it turns out it's for the best. A couple of dip switches sounds like a much simpler fix than changing out ballast resistors and electrolytics or swapping dial faces!!

But then remembering to calibrate the tacho properly in the first place would have avoided the problem altogether.............

Nigel