Slow or Low reading Tachometer

[TheMadBadger]

The tachometer on my ‘68 OTS reads slow, or should I say won’t go past 2500 or so rpm. It seems to be fairly accurate up to that point but won’t progress further up the scale regardless of engine speed. Does anyone have any ideas?

Regards
Mark Badger

[abowie]

If what you describe is correct then it's possible that there is a simple mechanical obstruction preventing the needle from turning (bit of dirt etc). Take the tacho out disassemble the movement from the case and have a look.

Otherwise, some light reading:

https://www.triumphclub.co.nz/wp-conten ... ters-1.pdf

https://www.classictiger.com/techtips/motach.html

[JerryL770]

I had this problem on my S2 FHC.

I have 123 ignition and thought this was an electrical problem but nothing changed in that way corrected it.

Thinking about it I realised the tacho would not go above ~2000 rpm as I accelerated but would jump up as soon as I lifted off.

This was caused by excessive float in the rotor so as the car accelerated, the rotor could move toward the tacho glass and then stick against the magnet body.

If you pull the needle off and remove the dial there is a small brass bearing (?) with a slot in, around the spindle. Turn this on its thread to screw it in till you reduce the spindle float to a few thou and problem cured.

[TheMadBadger]

I’ve fixed the problem by installing the Spiyda kit which replaces the electric components inside the tachometer. It works perfectly. Now I know I’ve been shifting at 3500 to 4000 rpm by sound!

Result!
Mark

[JerryL770]

Glad you have found the answer but there in lies the problem with your initial question: not enough information.

I presume from your post above that you have an electronic ignition. A 123 perhaps?

Had we known that, I might have pointed you in a better direction i.e. to the Spiyda RVI to RVC converter which I have in my own tacho.

[TheMadBadger]

My car presently has a Mallory points type distributor, which I will be replacing with an original distributor after I have it rebuilt. I also need to add back the vacuum port and line for the distributor. A previous owner deleted all of that.

Mark