Fitting Tachometer

[Lord Gadbury]

Hi All, 

I have a ford 1.8xld with Bosch alternator, also the boat has a smith industries tacho, which has never been connected. I have searched and found links from other sites, as I understand it the Tacho is wired to ground and to the 'W' terminal of the alternator. See pics.

As you can see from the alternator picture, the 'W' terminal appears to be missing, I am assuming that I will have to connect my own terminal her, probably by soldering. Is this correct ?

The second picture is from the back of the Tacho. Assuming this is the wiring diagram, single ind is a single alternator setup, dual ind, for a dual alternator setup. So if I am reading correctly, 'W' connector from alternator, to pin 1 of Tacho, pin 2 of Tacho to Ground. And now if I wanted to connect the second Alternator, then the same for pins 3 and 4 ?

If any one can just confirm or deny, been a while ( 18 years ) since working on this type of equipment. 

 

[Tony Brooks]

Are you sure that there is not a 6mm blade in the hole marked W? If there is not then I would not advise soldering anything unless you know how to set up a completely perseverate phase tap from one of the diodes. I do not know enough about the alternator but without the terminal I would be concerned what you see is a diode pack heat sink and not only will a connection there not work for a rev counter it is also difficult to solder to aluminium. Sir N would know more, try PMing him.

Are you sure the rev counter is designed for alternator use? I would expect three terminals and adjustment buttons/switches if it was. I fear its a petrol engine rev counter driven from the coil.

 

 

[Lord Gadbury]

Thanks for your reply, it isn't urgent so will do a bit more research, I am aware of adjustments, such as number of coin etc. Which I think the back of the Tacho has to come of, which as it as much use as a chocolate fire guard at the moment then I have no problems with doing. Can't remember what forum I read about soldering a new terminal onto, I think YBW, maybe the terminal is folded over.

[Tony Brooks]

You do have to solder if you want to fit a flying lead phase tap but its to a diode, not the heat sink.

Upon reflection I think that G one the diagram may indicate "generator". I hope this is supposed to mean a pulse generator that works lie a car's flywheel/crank position sensor. If so and if it will work with a phase tap one then termianl1 or terminal 2 will be connected to negative and the phase tap (W terminal) to the other one. However as it contains electronic circuitry I have no idea if it matters which one is which or if it will make magic smoke if wrongly connected.

Edited April 16, 2017 by Tony Brooks

[Lord Gadbury]

I was also thnking G = Generator, wiring diagram not the best.

I will put this on hold until I can have a chat with a friend next week, I will take the Tacho with me. I am pretty sure now that this Tacho is not fit for purpose, a different one will have to be acquired.

[Tony Brooks]

I think some Jags were fitted with an electric speedo where the sender was a little generator driven off the gearbox tail shaft. I also THINK that I have seen a similar generator on the end of a cam cover so driven by the camshaft. I expect the generator is a fixed field coil, spinning magnet type that produces AC so having rectified it in the gauge (thus no pos and neg signs) it would drive a moving coil instrument directly with no other power. If I am right then its not suitable unless you have the generator.

Having got into that train of thought I think I have seen such generators stuck into the mechanical revcounter drive take off on the odd marine engine.

[Jen-in-Wellies]

1 hour ago, Tony Brooks said:

I think some Jags were fitted with an electric speedo where the sender was a little generator driven off the gearbox tail shaft. I also THINK that I have seen a similar generator on the end of a cam cover so driven by the camshaft. I expect the generator is a fixed field coil, spinning magnet type that produces AC so having rectified it in the gauge (thus no pos and neg signs) it would drive a moving coil instrument directly with no other power. If I am right then its not suitable unless you have the generator.

Having got into that train of thought I think I have seen such generators stuck into the mechanical revcounter drive take off on the odd marine engine.

I fou nd a BMC 1.8 like this with a camshaft driven generator that supplied a Smiths tacho with both power and speed signal exactly as you describe. http://canalworld.net/forums/index.php?/topic/87426-tachometer-wiring/

The alternator was a type with no tach signal.

Jenny

Edited April 16, 2017 by Jen-in-Wellies

[Lord Gadbury]

Hi Jen,

Thanks for your reply, however mine is slightly different. Attached photo of complete rear.

 

[Jen-in-Wellies]

It does have four terminals marked 1, 2, 3 & 4, which is the same as the one I encountered. The G may possibly be for generator, which could be the same. It also doesn't have power and ground connections marked, which again is the same. It could be worth looking over the engine for a sender that goes with this. Take each timing pulley at the front and follow the centre line backwards and see if there are any unconnected two terminal gadgets on the engine that you don't know the function of. Are you sure this tacho was specifically for this engine?

Jenny

Edited April 16, 2017 by Jen-in-Wellies

[Lord Gadbury]

That's the problem Jenny, I am not sure, in fact I am swaying with the I am sure it is not.

However I will check over the engine, I am in there daily. Your suggestions are good, thanks. 

The Tacho only goes to 3k, pretty sure I have the 4800rpm XLD, not he 2800rpm XLD, However, this does make me wonder!