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Tach
- Thread starter Taz
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dklawson
Yoda
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The answer is you can probably find a later tach to fit. The other question you must ask yourself is do you want to stay with the same type of tach. My answer is "probably not".
Look on the face of your old positive ground tach. If you find the letters RVI on the face you have a current pulse sensing tach. Should you ever change to an electronic ignition (Pertronix or other) you probably won't be able to make this tach work.
If you look for a replacement tach, get a negative ground tach that says RVC on the face. These are connected a little different but are basically a "modern" voltage sensing tach.
Succinctly, the RVI tachs are wired in series from the ignition switch to the coil. If you replace an RVI tach with something else, you need to make the wire from the switch to the coil continuous w/o the RVI tach and its wiring. To connect the RVC tach you establish the same ground, switched power, and lamp connections for the tach. Then you run a voltage sensing wire from the tach to the coil (-) terminal.
Look on the face of your old positive ground tach. If you find the letters RVI on the face you have a current pulse sensing tach. Should you ever change to an electronic ignition (Pertronix or other) you probably won't be able to make this tach work.
If you look for a replacement tach, get a negative ground tach that says RVC on the face. These are connected a little different but are basically a "modern" voltage sensing tach.
Succinctly, the RVI tachs are wired in series from the ignition switch to the coil. If you replace an RVI tach with something else, you need to make the wire from the switch to the coil continuous w/o the RVI tach and its wiring. To connect the RVC tach you establish the same ground, switched power, and lamp connections for the tach. Then you run a voltage sensing wire from the tach to the coil (-) terminal.
It is not difficult to change a pos ground tach to a negative. The direction of the wire loop from the ignition switch to the coil needs to be reversed where it passes in back of the RVI tach and the tach needs to be opened and the wiring to the case and to the tab (power) connection reversed. You can get more detailed info searching for a tach thread on the forum.
George Zeck
Jedi Warrior
Offline
I just bought a late 60's / early 70's tach for my car and it seemed to work. Not 100% sure it was accurate. I've posted that the RPM's just seemed high. Still in break-in period of engine (shame on me for not blowing through that sooner) and switch from pos earth to neg ground.
The bad news was that my tach I bought on ebay did NOT fit -- although it seemed to work. Accurate ?? Since it didn't fit -- I jammed a screw driver to prevent it from bouncing out -- hit a bump and I heard a "pop" -- goodbye tach. So now I simply don't have one. (< 2 weeks ago).
I also wasn't comfortable with the swapping of wires inside (I looked and just didn't make sense despite help and links from many here)-- thus the purchase of a later model tach.
Anyone have advice on replacing with non-stock one without spending an arm and a leg ??
Tx-
Geo
/ubbthreads/images/graemlins/hammer.gif
The bad news was that my tach I bought on ebay did NOT fit -- although it seemed to work. Accurate ?? Since it didn't fit -- I jammed a screw driver to prevent it from bouncing out -- hit a bump and I heard a "pop" -- goodbye tach. So now I simply don't have one. (< 2 weeks ago).
I also wasn't comfortable with the swapping of wires inside (I looked and just didn't make sense despite help and links from many here)-- thus the purchase of a later model tach.
Anyone have advice on replacing with non-stock one without spending an arm and a leg ??
Tx-
Geo
/ubbthreads/images/graemlins/hammer.gif
lesingepsycho
Jedi Warrior
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Let me be blunt. I'm not interested in having a stock MG Midget.
That being said, the A-series engine is stout and strong yet delicate, meaning, it doesn't take much out of normal operating range to do damage. Therefore, I wanted the most reliable and most accurate gauges that I could find so that I could monitor every infinitesimally small detail of what the motor was doing at any given time. Therefore, I chose autometer gauges and they have SAVED my engine TWICE since using them. Once when the oil plug fell out and once when the car nearly boiled over. Especially the temp gauge I had zero confidance in being the old copper tube style.
I chose the ultra-lite model which is a little more modern looking but like i said, I'm not interested in having it look like a stock or vintage car but I also imagine that if you wanted to upgrade, you could find autometer gauges or any other decent aftermarket gauge that had more of a "stock" look. As far as costing an arm and a leg, well... they're expensive but not as much as a rebuild!
For those interested, I've attached a picture of my dash or you can see it on my web page
JACK
That being said, the A-series engine is stout and strong yet delicate, meaning, it doesn't take much out of normal operating range to do damage. Therefore, I wanted the most reliable and most accurate gauges that I could find so that I could monitor every infinitesimally small detail of what the motor was doing at any given time. Therefore, I chose autometer gauges and they have SAVED my engine TWICE since using them. Once when the oil plug fell out and once when the car nearly boiled over. Especially the temp gauge I had zero confidance in being the old copper tube style.
I chose the ultra-lite model which is a little more modern looking but like i said, I'm not interested in having it look like a stock or vintage car but I also imagine that if you wanted to upgrade, you could find autometer gauges or any other decent aftermarket gauge that had more of a "stock" look. As far as costing an arm and a leg, well... they're expensive but not as much as a rebuild!
For those interested, I've attached a picture of my dash or you can see it on my web page
JACK
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dklawson
Yoda
Offline
Taz, when you converted your tach to negative ground, did you find a potentiometer on the circuit board for calibration? If so, you can adjust the gauge to make it read more accurately. You'll need another tach you trust as a reference. Just hold the engine at some reasonable RPM (like 3000 as displayed on the reference tach) and adjust your Smiths to match it.
George, if you're looking for reliable stuff to replace your Smiths tach (on a budget) look for used VDO and Veglia-Borletti gauges on eBay. There are lots of VDO tachs available, some from Porsches may even be about the right size. The Veglia gauges come from Fiats and Lancias and are known to be very stable.
George, if you're looking for reliable stuff to replace your Smiths tach (on a budget) look for used VDO and Veglia-Borletti gauges on eBay. There are lots of VDO tachs available, some from Porsches may even be about the right size. The Veglia gauges come from Fiats and Lancias and are known to be very stable.
George Zeck
Jedi Warrior
Offline
I ended up biting the bullet (racers will probably slap me) but I bought a VDO 4" tach from Summit for ~ $90 delivered. More than I wanted to spend -- but I can trust this and it fits and it reasonably "matches" the other guages (w/o the color in the red zone).
Tx-
Geo
Tx-
Geo
George Zeck
Jedi Warrior
Offline
For complaining about spending $100 and thinking it's "big $$".
I did see the ones on ebay @ $20 but they just wouldn't have looked good. (white face w/ red flames and I'm not 18).
Tx-
Geo
I did see the ones on ebay @ $20 but they just wouldn't have looked good. (white face w/ red flames and I'm not 18).
Tx-
Geo