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MG MGA - MGA Rev Counter

Hi Everyone,


What are the things to check for now that my Rev Counter appears permanently to be stuck at zero..?

It was working fine previously.


Thank you




Aleks
Aleks Stojanovic

Hi Aleks,
assuming you are running a 3-brg engine with a mechanical drive rev counter, it seems like the rev counters drive cable is no longer connected.
In theory, the connectors either at the rear of the rev counter or the engine end could have come unscrewed, but most likely is that the inner drive cable has broken.

If you disconnect one end, you should be able to pull out the inner drive cable with a pair of mole grips.

Once it is out, have a look at each end, both ends should have be square in section to connect to the engine drive or the rev counter. It is fairly obvious if the cable has broken.

You can in theory, just fit a new inner drive cable, but you are best advised to replace the entire cable (inner and outer) because the outer can be also be damaged if the inner has broken.

Moss can supply new cables.

If the inner cable is not broken or disconnected, it could possibly be a problem with the rev counter internals, but I personally have never come across this.

Let us know how you get on.

Cheers
Colyn


Colyn Firth

Sorry Colyn,

My apologies - I should have said that I have the MGB 4 stroke 1800 engine, with an electronic distributer.

Thank you for your advice.



Aleks
Aleks Stojanovic

I run with a Smiths RVC 2415/00F model tacho from a 5-bearing MGB (or an MG midget), mine is the negative earth model and it has "negative earth" printed onto the dial at the bottom.

You can find the wiring instructions on the MGA Guru website. I am fairly sure that on this model there are two connections, a spade connector for the +12v ign supply and a push on connector for which goes to the negative connector on the coil.

The RVC tacho needs a separate +12v supply from the ignition, don't be tempted to use the +12v supply from the coil as this may affect the rev readings.

Cheers
Colyn

Colyn Firth

Hello Aleks

When I built an 1840cc 18V engine for my 1600 Mk1 in 2012, I fitted an RVI tacho. It required similar connections to those mentioned by Colyn, but mine required a loop from the coil-to-distributor wire to pass through a magnetic coupling on the back of the tacho.

I persisted with a number of RVI tachos until 2018. They use germanium transistors, and the circuit boards are often fragile and subject to easy damage when replacing components.

In 2018, before our regular MGA trip to Italy in May, I again had RVI tachometer problems, and decided to fit a Spiyda tachometer drive unit. This powers the RVI meter movement only. The RVI electronics are not used. As long as your tacho movement is OK, you can use the Spiyda unit.

https://spiyda.com/tachometer-electronics.html

I mounted the Spiyda module external to the RVI case under the dash, on and above the dash stiffening bracket near the steering wheel, together with a screw terminal strip for the various connecting wires. (Can mail photo if you wish.) You calibrate the assembly via the Spiyda website before fitting it in the car.

This has worked perfectly since. I recommend it. Not expensive, GBP43-00.

Mike Card

PS How are those brake calipers going?
M D Card

Aleks
If it was working fine previously, my money is on a connector (wire) has fallen off the back of the tacho

willy
William Revit

I can certainly recommend Spiyda products,
I fitted a Spiyda Gauge Wizard to calibrate my MGAs fuel gauge and it is now accurate to within a pint or two.
You would have to have to have your Tacho tested to make sure that it is working correctly before you invest in the Spiyda Tacho unit though.

Cheers
Colyn
Colyn Firth

This thread was discussed between 12/03/2023 and 14/03/2023

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