There is an alternative! I had the problem of converting my MGB 4 cylinder
tach to an 8 cylinder. So I bought ($10) a Triumph TR8 tach and swapped
out the guts to the MGB one. The MG dial fits perfectly onto the TR
guts! Maybe a 6 cylinder tach could offer its guts to fit ? The only
problem was drilling the holes in the MGB tach body in the right place -
but mistakes do not show !!!! The potentiometer method seemed to require
calibration with equipment I do not have.
At 02:09 AM 2/27/2005, Paul Hunt wrote:
>The 65 originally had a current pulse tach. This has a 12v and ground
>supply on green and black wires, and the current pulse is obtained from a
>white looped through an inductive pickup en route from the ignition switch
>to the coil +ve or SW terminal. The earliest of these had a physical loop
>of wire from the loom that was placed in the external pickup, later versions
>had two separate whites with male and female bullets on the loom, the tach
>having an internal pickup with flying leads or the bullets mounted on the
>case. Later tachs (73 on) were voltage operated and had a single
>white/black from the coil -ve to the tach in place of the white loop. You
>need to determine what type of tach you have and if it is connected
>correctly to whatever ignition system is on your engine. If electronic
>ignition or fuel injected with an ECU you could well have problems with the
>current pulse tach, this is not uncommon with aftermarket electronic
>ignition systems on the standard engine. You stand a better chance with the
>voltage operated tach, but it all depends on the ignition system for your
>engine.
>
>Since there are plenty of references around to converting standard tachs for
>a V8 by adding a multi-turn pot in the appropriate place I see no reason why
>this shouldn't work for a V6 with a suitable ignition system. V6? 3 firing
>pulses per revolution? 1000 revolutions per minute? 50Hz? I've not done
>it but again I have heard of using a simple battery charger with a simple
>rectified (and not smoothed) AC output as a test signal for tachs, 50Hz if
>single wave, 100Hz if full-wave rectified.
>
>PaulH.
>
>
>----- Original Message -----
>From: "Richard Schultz" <schultz2146@earthlink.net>
>To: "MG List (E-mail)" <mgs@autox.team.net>
>Sent: Saturday, February 26, 2005 8:32 PM
>Subject: MGB 65' v6 231 conversion alt/tach problem
>
>
> > ... I recently acquired a 65' mgb that had the 231 v6 conversion.
> >
> > Like I said I have a Smith Tach. The needle does not deflect at all when
> > engine is running at any speed.
> >
> > Checked the 12VDC source that comes to the tach. Question. since I
>should
> > see a pulse from this 12VDC, what AC source should I be seeing from same
> > lead and at what freq for 1000 rpm?
>
Regards
Barrie
Barrie Robinson
(705) 721-9060
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