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MG MGB GT V8 Factory Originals Technical - Tach Conversion


I have a 74.5 MGB Rover 3.5 conversion.
I used Leon Zaks instructions to convert my tach to operate for 8 cylinders.
One of the electrical parts has failed and I need to source another one. The local Radio Shack store is unable to help me, the local Electronics’ fellow would gladly research the part (and change me 40 bucks per hour to do so) or I can hope that some one on this board can help.
The part I need can be seen at
It is the right hand side orange capacitor, resister (I am sorry I don't know the proper terminology).
Would anyone be able to give me the proper name, value and perhaps where I can get such a part?
As the concentric springs in my tach are somewhat messed up (it still works) I am also trying to source a new tach. Does anyone know what numbers (on the tach face) I should be looking for that allow the tach to be converted to run for an 8 cylinder?


Bruce Mills


Here's another option for you. I'm using one in my tach for my v6 and it works great. The board pictured is a completely new circuit that bypasses the original B tach circuit. Theo Smit is great to deal with as well. Tell him what you are trying to do and he'll take care of you.

-- Scott
Scott Costanzo
should be dead cheap

Any of the tachs from '73 to '76 can be modded to work with the Zak modification. The late ones can be done also but they won't fit your dash. How did you determine that the that part is bad?

Thanks Scott and Peter. Both good sites.
"Any of the tachs from '73 to '76 can be modded to work with the Zak modification."
Thanks Jake, that is what I wanted to know. With that I can get the tach numbers for those years. Although there doesn’t seem to be much advertised in the local Buy & Sell, the BBS classified or even Ebay. I am now thinking VDO gauges might be nice to have. They would save having to have another ratio drive (tranny to speedometer) made up when I change the tire size and/or the rear end.
I have had trouble with the concentric springs inside the Smiths tach for years. Every once in a while I will hit a bump and they will jump over the separator between the 2 springs. I have always managed to get them back but now they are really starting to look tired.
When I had the tach apart the ‘pot fell off so that was going to need soldering, as I looked at the electronic components I noticed that one of the resistors/capacitors was broken, cracked right through the middle. So time to get a new tach

Bruce Mills


I used the mechanics and electronics of an early SD1 instrument and fitted it into the housing of the normal MG B tach.
It is just a change, all screws are in the same position and the connetors too.
Just change to your old dial and pointer and forgett all tricky changes to the old printed circuit that do not really work well (variable in line resitor etc.).


This thread was discussed between 15/09/2006 and 18/09/2006

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