Tachometer

[series2]

I have a Smiths revcounter in a 1967 Series 2 which reads at least double the engine revs, 8000 rpm for a 1300Xflow is unlikely. I manged to buy an old but brand new boxed Smiths revcounter of the right period but this also overreads by a similar amount. Any ideas for what could cause this.

[Dave H]

Mike,

I had a similar problem with my Xflow (1987 car - engine lots older). The problem was explained to me as the Rev counter picking up multiple signals from the coil. It was some years ago and all I remember was a number of different configurations of coil/resistor were tried before the whole thing was dumped and an electronic ignition unit installed. (Which solved starting problems as well). I would advise you take it to a good auto electrician who should be able to diagnose your problem.

[R2D2]

The earthing on early cars is poor and all of the instruments use common earths. I would start by using a clean earth directly from the battery and then using a screened cable from the coil.

There is a plug in the back of the instrument which hides an adjustment potentiometer and lets the instrument be adjusted but you would need a reference from a master instrument such aa a Crypton or Sun system if you change the calibration in this way.

[CHRIS CLARK]

The electronic ignition didn't cure all the starting problems eh Dave? Love to Shazza!

[James Arnold]

I had a very similar problem with a 1970 TVR Tuscan V6. The Rev counter showed too many rpm. After spending money on a new Elliot rev counter, I discovered the reason was due to the car having been converted from a ballast resistor ignition system.

The rev counter was calibrated to work with a low tension circuit voltage of less than 12volts. When the resistor was removed, the rev counter over-read (and points had a short and sparky life).

I have no idea whether a series 2 had ballast resistor ignition when new, but its a ford engine from the same era as my TVR.

I believe that ageing rev counters are usually horribly inaccurate, I seem to remember that there are specialists who will put modern movement into the old case.

J