Tachometer

[Timothy Keith-Lucas]

My original tach is toast in several ways. I'm trying to find a replacement.  So far I'm the not-so-proud owner of two (2!) positive earth Smith originals that apparently came off bug eye sprites and are 95mm in case diameter. That's too big to fit between the upper frame member of the dashboard and the steering column.  I need an 80mm. Moss has one, but it's negative earth. Can anyone tell me where to find an 80mm, positive earth, electric, 8,000 RPM tach for a Series 2 Seven? Anyone want the ones I've got?

 

Thanks. --Tim.

[toldfield]

Try Nisonger

 

https://nisonger.com

[MV8]

I wonder if you could not just take a common, neg ground tach and loop the coil lead a few tight turns around a plug wire to trigger the tach.

[7Westfield]

FWIW   Bugeyes were mechanical, driven from the generator

I don't recall when they went electric

[MV8]

Late '60s MGB was still positive earth. Don't know if the tach on those is smaller.

You can use a negative earth tach on a positive earth car.

The main difference is you are controlling it (off-on) by the tach ground through the ignition switch with the tach power and light wires connected to the chassis. Because the negative is not split, the light would illuminate anytime the tach was ON but it could be wired in such a way to make the light independent of the tach being ON.

The bottom line is the tach is still getting positive and negative on the correct terminals. 

Edited August 7 by MV8

[7Westfield]

the older tach's usually ground thru the case, instead of a separate wire, so you would need to insulate the case from the dash

not easy to do

 

there used to be places that would convert a tach for you, but I think most of them are gone, and it wasn't cheap

I think Nisonger was one, but they are out of the repair business

 

there are 2 types of smith connections--earlier ones used a loop of the lead from switch to coil going thru a plastic clip on the back to generate a signal. you had to have the loop going the "right" way for it to work

later ones had 2 push on connectors for the wire and the loop was internal

 

your ideal solution is a tach from a later MGB, if you can find someone to convert it

you might try a place in Albuquerque   I think it's called Albuquerque Speedometer

I first dealt with them in the 80's   I was going thru town in my Corvair and the speedo crapped---he fixed me that day

BUT   I tried to get something done a few years ago, and both price and time were ridiculous   YMMV

 

call Moss--maybe they know a guy, who knows a guy....

Edited August 7 by 7Westfield

[7Westfield]

OR     do the conversion to neg ground

 

just re-polarize the generator       switch the coil wires     starter doesn't care

only issue might be the fuel gauge, if you have one

[Timothy Keith-Lucas]

So, no nice clean simple solution. The conversion to negative ground is getting more attractive. Nisonger was not helpful, just a "unfortunately" message. I found this negative ground tach that will fit and looks about right for $200.

 

https://www.appletreeauto.com/80mm-0-8000-rpm-tachometer-with-chrome-bezel

[Timothy Keith-Lucas]

I'll just have to insulate it very carefully and switch the wires.

[7Westfield]

1 hour ago, Timothy Keith-Lucas said:

I'll just have to insulate it very carefully and switch the wires.

before you do, check into whether the reversed polarity on the signal wire will be a problem

hate to have the smoke leak out...

[toldfield]

My apologies for the Nisonger reference...  But I'll try again.  North Hollywood Speedometer is very highly rated.

https://www.nhspeedometer.com/

 

[MV8]

I did not suggest reversing polarity. A pertronix mag or optical pickup should float allowing the use of a negative coil trigger with a positive earth chassis. Could also use a signal conditioning circuit to go between the neg earth tach and a positive earth coil being triggered by points.

 

They also have cheap digital inductive tachs run on batteries that wrap around a plug wire that can hide under the dash for when you really want to know the revs. Trust me; they are HIGH at highway speed.

Edited August 7 by MV8

[Alex-Ks1]

On 8/7/2025 at 11:16 AM, Timothy Keith-Lucas said:

So, no nice clean simple solution. The conversion to negative ground is getting more attractive. Nisonger was not helpful, just a "unfortunately" message. I found this negative ground tach that will fit and looks about right for $200.

 

https://www.appletreeauto.com/80mm-0-8000-rpm-tachometer-with-chrome-bezel

What ever you do , don't buy Chinese crap , they all  degrade in time , they might look good and are cheap as dirt but junk 

[jbcollier]

Fit a repair kit from these people:

 

https://clocks4classics.com

 

Works a treat.

[IamScotticus]

If originality is the goal, my suggestion is not helpful. 

Racetech (UK) have a 80mm electronic speedo and tach set.  The speedo is capable of GPS and motion sensor (magnetic?).  This makes ths elimination of the speedo cable possible.

The electronic versions are only available in black face and bezel, for now.  

Imagine life without a cable!

 

I have heard that Smiths had a GPS speedo, but I haven't seen it and the online store fronts haven't been helpful. 

I need to do more Googling on it.

Edited August 9 by IamScotticus

[IamScotticus]

2 hours ago, jbcollier said:

Fit a repair kit from these people:

 

https://clocks4classics.com

 

Works a treat.

I didn't know "Tickety-Boo" was a thing!

[Croc]

2 hours ago, IamScotticus said:

I didn't know "Tickety-Boo" was a thing!

 

It is but I would never describe you as tickety-boo.  I could use many other words.... 

[Timothy Keith-Lucas]

Are you children having fun?

 

Actually the trashed tach I have was converted to new electronics by Clocks for Classics. Unfortunately, I need a quicker solution. Let me see what I can do switching wires  and insulating, with the hope that my 7 will not become a poster for Lucas Electric (not relatives).