Series 1 Tachometer Function (S3 motor)

[Demian]

Hello again

Series 3 motor in an otherwise completely original Series 1 … including distributor and transmission.

Tachometer not functioning.

Can’t seem to find anything quite related searching…

What do I need to make it work?
What makes it work?

I recall on my E Type and Mk2 it ran off of cam with a little generator …
The Series 3 XJ was electronic and used later BW 65/6 transmission…

I’ve read the Series 1 Tach is different and larger than the later S2 and 3 models.

Prior to tackling this, is there anything else i need to know not mentioned within this excellent post by Mr. Doug Dwyer? It is related to the Series 3 however…

[xj] Tachometer

My tachometer quit working a few weeks ago so last night I decided to pull it out and take it apart. I re-soldered all the contacts, cleaned with electric parts cleaner, lubed the shaft with white litho spray, cleaned the lens and reinstalled. Still no tach. readings. Do these go bad or should I look for a wiring or fuse problem? Any suggestions? I know I’ll have to clean the rest of the gauges now because the lens and face plate looks better than the rest. I wonder what other can …

THANK YOU very much once again.
It is genuinely appreciated.

[Frank_Andersen]

**
There is no ‘motor’ as such in the tacho, Demian…

The tacho is connected, white slate/blue, to - and receives signals from coil negative. It also has 12V power on green wire - which actually ‘drives’ the tacho. The ign amp connects the coil to ground to ‘charge’ it - then breaks ground to fire the spark. This gives a signal to the tacho in step with engine rpms - and the needle deflects accordingly…

If you have ignition; the ign amplifier works, and the tacho should - if working, and properly connected. Check coil connection for continuity and proper connection of wires at the tacho.

Any previous history as to when the tacho failed…?

Frank
xj6 85 Sov Europe (UK/NZ)
**

[Demian]

Thank you Frank.
Think you’re confused…or I am??

The “motor” you seem to have thought i was mentioning was the old generator type gizmo run on the end of the cam on earlier cars mentioned (?) I did’t believe there was any motor within the tacho…

Tach never worked since I’ve owned the car and it was received in this state (S3 motor).

However, remember, this is a Series 1 car. no ignition “amp” as on the S3 and FI cars, etc…if that is what you were referring to?

Other than motor(engine), otherwise all original Series 1. Carbs, transmission, etc…Mistakenly I believed tach ran off of transmission which is why I mentioned it above, that’s the speedo I was thinning of…it’s late!

Earlier cars I’ve had (E Type and Mk2) had this generator gizmo on end of cam which ran the tach).
Don’t know if Series 1 XJ6 did as well…

Mentioned S3 motor(engine) only because it does not have cam machining at rear end as the original S1 motor should the tach have originally run from there using the little gear generator as on earlier models as stated…the S3 XJ6 cam cover is flat in the back…if that makes a difference with the old tachs that ran there…I can’t remember anymore.

So, does the original S1 tach run off the neg terminal coil terminal as well like the XJ6 per that post?

EDIT:

Solved and important. The S1 Tach does NOT go to the Negative Coil connection like the S3 apparently…

Per a past post found and responded to by no other than YOU Mr. Frank.

Found within some Post entitled “Loose Wires and Mystery Relay” (?!)I came across this:

Hold it, Steven - and procede carfully, very carefully…

On the SIs the coil pos goes through the tacho, for some obscure reason.
This means the tacho wire is live, and conncting it to coil neg will
effectively ground it - and zap…
If you cannot discern wire colour disconnect it from the coil, measure
voltage - then turn on ignition and remeasure. If it has 12V at any
time; do NOT(!) connect it to coil neg…

Point here being; the wire on the ‘other side’ of the resistor should be
from the tacho, and carry 12V with ignition ‘on’. The resistor should be
checked by disconnecting all wires and measuring resistance in it -
likely some 1 - 3 ohms. Break or contiuity is a defective resistor - and
may be one reason for PO wire machinations…

[Frank_Andersen]

**
I stand corrected, Demian - I thought you had the electronic ignition…

The procedure mentioned in the ‘Steven’ post is appropriate. The ignition type mentioned is indeed fed trough the ignition coil through the tacho. The current flows through a coil inside the tacho, and move the needle electromagnetically.

Incidentally, this arrangement causes some problems when changing to electronic ignition and retaining the original tacho…

Frank
xj6 85 Sov Europe (UK/NZ)
**

[Demian]

Thank you…got it.

Yes, I’ve seemed to come across that in past posts…problems with the electronic ignition changeover and the tach.

Have a good day and thanks again very much for your time.