16 replies to this topic

[Vanman20]

Fitted a Smith's rev counter out of a 4 cylinder Triumph.Wired in with a 12 volt feed and it under reads by about half.
Wired in from the the voltage stabilizer and it's all over the shop.
Any guidance much appreciated

[nicklouse]

what is your ignition system. are you 100% sure it is from a 4 pot engine?

[Vanman20]

what is your ignition system. are you 100% sure it is from a 4 pot engine?

Std MG Metro,non electronic.
Yes definitely 4 cylinder,says on the fascia and written on the housing is Dolomite/Spitfire/Midget so it must have come from a breakers

[KTS]

Std MG Metro,non electronic.

 

 

you sure it's non-electronic (i.e points) ?   MG metro, I think, would as standard have been fitted with the 65DM4 type distributor which used the electronic switch module

[Vanman20]

Std MG Metro,non electronic.

you sure it's non-electronic (i.e points) ? MG metro, I think, would as standard have been fitted with the 65DM4 type distributor which used the electronic switch module

It has points,59D dizzy

[nicklouse]

 

 

Std MG Metro,non electronic.

you sure it's non-electronic (i.e points) ? MG metro, I think, would as standard have been fitted with the 65DM4 type distributor which used the electronic switch module

It has points,59D dizzy

 

The turbo came with Electronic but not the MG.

 

pics of the back of the rev counter or any ID info would help.

[Chris1275gt]

Is it wired to dash voltage stabiliser as that is stabilised at 10 volts not 12v don’t I know if that would make it not work properly.

[Vanman20]

[sonscar]

Is this one where the 12v for the coil passes through it in series before going to the coil?is 12v switched supply,,,rev counter ,,,then +ve of coil removing the current feed.Just a thought,probably incorrect,Steve..

[KTS]

http://www.mgb-stuff.org.uk/tach.htm

 

..about halfway down the page looks like yours

[sonscar]

Looks look the above,I was thinking of the earlier version.You need 12v unregulated and connect to the negative of the coil.These are old and work poorly as a rule,Steve..

[Vanman20]

It does seem like the voltage stabilizer is messing with stability lol.
But even with a 12v supply it under reads.
Maybe someone has had it apart before and put the needle on in the wrong position....or maybe I'm clutching at straws and it's knackered

[sonscar]

Isn't there a test using a battery charger that gives you 3000 rpm?Must google it,Steve..

[Spider]

Those tachos need a 12 V supply. It's an RCV type of Tacho. I have found inside them there is a pot for calibrating, but if opening it up for adjustment, I'd suggest replacing all the Electrolytic Capacitors too (there's only one or 2 of them) as they'd likely be on their last legs by now.

You can calibrate the unit yourself, find yourself a 12V AC Plugpak (or transformer), connect that between Earth and the Pulse Input Terminal. In the UK, it should read 3000 RPM and in the US, 3600 RPM.

[Vanman20]

Those tachos need a 12 V supply. It's an RCV type of Tacho. I have found inside them there is a pot for calibrating, but if opening it up for adjustment, I'd suggest replacing all the Electrolytic Capacitors too (there's only one or 2 of them) as they'd likely be on their last legs by now.

You can calibrate the unit yourself, find yourself a 12V AC Plugpak (or transformer), connect that between Earth and the Pulse Input Terminal. In the UK, it should read 3000 RPM and in the US, 3600 RPM.

Tried that but don't get any reading.....googling suggests this needs to be done with the coil or a bulb wired into the circuit