Tachometer

[Mogzy Malone]

Hi, new member alert.
I bought my self a morris minor earlier this year.
I've recently acquired a tachometer to hopefully add to the dashboard eventually. As I am a fool I did not do the proper research prior to purchase, not taking into consideration the fact polarity may influence the workability of the gauge. It arrived today and I have struggled to find a datasheet, or installation guide.. however looking online I'm seeing that many older tachometer are built to work with positive earth.

As I have recently made a modification to my morris 1000, installing a altenator, for the sake of practicality. My car is now a negative earth. Question is.. have I just bought a gauge that unfit the job at hand?

Any ideas of the particular set up of this tachometer from the images attached

[King Kenny]

It looks like it is cable operated so polarity won't matter. However,I would not know how to connect this gauge to your gearbox.

[ManyMinors]

It does indeed appear to be cable driven. Possibly from a Riley 1.5? It won't be any use to you unless you find a way of driving it - which I don't think you will on a Minor. The rev counter was driven from a fitting in the engine block on the Riley and, I seem to recall, from the dynamo on the original Austin Healey Sprite? The rev counter counts the revolutions of the engine so is not connected to the gearbox

Oh, And welcome to the MMOC!

[mobylette]

https://www.ebay.co.uk/itm/153766632800

[geoberni]

Clearly a mechanical gauge, it's got a spindle in the centre, so it's designed to go with a specific connection on the engine or gearbox.
That's almost certainly a 1950s Tacho, from something like an MGA.
It's from an era where only Sports Cars had a Rev Counter, as far as I'm aware, they didn't start fitting them to 'sportier' common cars like Mini Cooper etc, until electric ones became available in the early 60s, using magnetic pickups to generate a pulse which could be counted.

I don't even think the A series engine could be fitted with a mechanical Tacho; they were B series engines in the MBA/B, Riley, Wolesley etc
See this photo I've pulled off the web. B series 1500, Tacho cable connection point arrowed.

Rev Counter connection.JPG (100.92 KiB) Viewed 4397 times

[philthehill]

The 'A' Series could be fitted with a mechanical tacho with the drive off the dynamo (as mentioned above) or from the front of the camshaft via an adapter fitted to the timing chain cover.

[geoberni]

The 'A' Series could be fitted with a mechanical tacho with the drive off the dynamo (as mentioned above) or from the front of the camshaft via an adapter fitted to the timing chain cover.

Didn't know that, never seen or heard of it.
Was that how they started with the Mini Coopers etc? I thought they were always electromechanical ones.

I've double checked my Lucas manual for Dynamo servicing and there is no mention of any mechanical add-ons for driving a Tacho, but I did find this image on ebay of the fitting ... every day's a school day...

Tacho Dynamo.JPG (88.59 KiB) Viewed 4356 times