Have i screwed my tacho?

[Goughie]

My Capri has always ran a complete SD1 tacho housed in the original Ford binnacle, i never liked the look of it as the needles and dials didnt match. I noticed that the normal Capri rev counter had the markings in much the same place so removed the needle from the SD1 placed the Capri face over it then redrilled the Capri needle to fit, Looks fantastic! The only problem is, it doesnt work any more
Mentioned it to a guy at work and he said some tachos are sprung loaded and by removing the needle would lose the tension? Can anyone confirm this is correct?
The other snag is, i done this whilst i was swapping the engine, was 3.5EFI
now 3.9 running a Holley so i dont know if that could be part of the problem. With my limeted knowledge i have put a multimeter on the terminal on the back of the gauge and get voltage which increases with RPM, is this how they work?
Thanks in advance,
Paul

[ChrisJC]

They work by measuring the frequency of the on-off-on-off...... signal from the coil.

It's almost certainly a mechanical problem.
The shaft is indeed sprung loaded, always trying to return the needle to 0. The stop-pin prevents the shaft from turning too far. If you've removed the needle, the spring will have completely unwound!

You're best bet is to hook it up to a running engine (with a known engine speed, e.g. a working rev counter), take off the needle and put it back on in the right place.

That might work anyway!

Chris.

[Goughie]

Hi Chris,
Sorry for the late reply and thanks, will take the needle back off and see if the spindle moves at all when the engine is revved.
How do you get round this problem if you are fitting a white dial kit i wonder? and is it possible to convert a standard 2.8i 6 cylinder tacho to read off an 8 cylinder engine?
Thanks again in anticipation,
Paul
P.S. has anyone got a spare MK2/3 Capri bonnet in the Coventry area, condition not that important, gonna cut a big hole in it for my bugcatcher