4.2L 2+2 Tachometer generator

[Allister]

Hi guys,

The tachometer of my 1968 4.2L 2+2 has been overhauled twice by a specialist, via David Manners Ltd, in UK. But these overhaulings didn't resolve the problems : the tachometer displays erratic values, never the same one for a same speed !!

I wonder if the problem could come from the tachometer generator. For example, I know that the 340 mkII tachometer generator is located at the end of one of the camshafts. Where is it on my E Type please ?

Kind regards,

Julian

[Allister]

I have to notice that the speedometer is perfectly working, checked up with a Sat Nav App on my Smartphone

[Tom W]

There’s 2 versions of tacho on the E-type 6cyl.

Series 1s have the same generator driven system as you mention on the MK2. The generator is on the back of the inlet camshaft.

Series 2s have an RVI tacho that counts ignition pulses on the positive wire going to the coil. These can read incorrectly or erratically if the car is converted to electronic ignition.

[abowie]

Your car doesn't have a tacho generator. As above it is an induction/RVI unit which takes its signal from a loop of the ignition wire going to the coil.

Send it to Speedograph Richfield in Nottingham, UK.

[Series1 Stu]

I think Julian is referring to what we commonly call the speedometer. It's a bit like the Tachymeter scale on your watch bezel.

The clue is in calibration against Sat Nav. An erratic speedometer needle is commonly caused by problems in the cable drive.

Regards

[mgcjag]

Julian,s second post confirms that his speedo is working ok when checked with his sat nav...Steve

[Series1 Stu]

Ah, yes. My mistake.

Regards

[christopher storey]

Allister : often, the symptoms you describe with an RVI ignition driven tacho are caused by inadequate earthing. The case can be earthed with a wire connected to the nuts which hold the tacho to the instrument panel. These nuts need to be quite tight to get a good earth

The other cause, however, as already stated, is that the tacho is not compatible with any electronic ignition unti you may have installed