Tacho fitment on a mini!!! (hhhmm.....Mexican food)

[Doug Jackson]

i.ve recently fitted an old smiths tacho to my mini(1975 850). It very keen and wildly optimistic. Over reading by 1 1/2 times. Its wired in series in between the coil and the Dizzy. Is this correct?? not a low level missle (Lotus 7) related question....but you're a wise bunch.

 

 

[Super_Rich_Bernie]

Electronic tachos count pulses in the ignition. Did this one originally come from a 4 cylinder car?

 

Jonathan

[Doug Jackson]

Hi Jonathan

 

Yes...the dial says clearly on it 4CYL. Although i did hear a rumour once about Tachos bieng wired differently in the old days(teehee). This piece of kit is 60's accessory...in torpedo shaped indervidual binncle thing....nice!

[Morls]

"You're a wise bunch"

 

I take it they couldn't help on Sylva Chat then wink.gif(That should bring Coose back to Blatchat).

 

I thought one wire went to the LT coil side and one to earth, i.e in parralell with the coil, otherwise all the LT side current would have to travel half way round the, (admittedly small), car, theoretically weakening the spark.

 

I'll go and have a look for a manual....

 

Anyhoo, Shouldn't you be at work at this time of day?

 

Mark

[Morls]

Ok,

 

the two examples I can find, both using Smiths clocks (miserable, mancunian things waving gladioli and moaning about underpasses and wanting to cry), show three connections:

 

1- To earth, this may well have no insulation between the terminal and the body of the tacho.

 

2- To a power supply, stabilised. Poss not fitted on yours.

 

3- To the coil LT connection, where the dizzy connects on to it.

 

If it blows up once connected:

 

1-drill a hole through the back & drill a hole through the windscreen, (dont forget to use a grommet).

2- Put heavy curtains round all windows and connect a dremel flexi drive from the needle to the camshaft.

3-Paint a white mark on the clockface and use a strobe light connected to a signal generator to "freeze" the needle over the white mark.

4-When the signal generator is set to 240Hz the engine should be doing about 7200rpm.

5-Get a feel for the degree of valvebounce at this engine speed.

6-Change up a gear whenever this noise happens.

 

smile.gif

 

 

Mark

[Doug Jackson]

Oh you wise old sage.....I know you'd resort the the old dremmel method eventually!!!!

 

I think the following info may be true::

 

Before 1974 (approx.) the electronic tachometer were current impulse triggered. This means that the tachometer sense wire is connected in series with the ignition coil, usually between the ignition switch and coil/ballast positive as in Fig 1. Sometimes the power for the tachometer was shared internally with the ignition switch end of the sense wire giving only three terminals. Smiths unit of this type can be identified by the letters RVI on the face of the tachometer. Designed in the days of contact breakers, they give inconsistent results when used with electronic ignitions. Many installations will work but some will produce erratic or no movement of the indicating needle. Some suggestions for rewiring the ignition circuit to eliminate the problem have been tried with limited success

 

 

 

but i havn't read it. To many long words and quite frankly the first sentance is not exacly gripping.

 

So i've done it wrong then?

 

Looks v.goog@piontlessaccessories.com

 

p.s. I am at work although not doing any!

 

hows the hunt for the brackets going for you car mounted visor?

[Morls]

I can't say if you've done it wrong as I too lost interest after the first line.

 

Despite a 9 second scan read I couldn't see the word "Dremel" so perhaps it recommends a chain coming through a slot in the bonnet, driving a go Kart axle which has one wheel removed so the spline drives the tachoquestion.gif

 

I really can't be sureconfused.gif

 

As for my Aeroscreens, I might just paint arcs on the windscreen instead.

 

The proper ones are making the bookcase look very Vintage and Sporty. Just choosing a cookery book makes me feel like I'm driving a Bentley round Brooklands.

 

I am very sad.

 

Mark