5 replies to this topic

[BiMU]

Before I buy a rev counter I thought I'd pick peoples brains. I was wondering what the differences are in rev counters/tacho gauges as there? Like RVI, positive earth etc... as I haven't got a scooby doo!

[GreaseMonkey]

The figure above is helpful if you are fitting a Smiths RVI type tachometer to a car with a points-type distributor. (RVI will be somewhere on the gauge face). If your car has electronic ignition, do not bother trying to fit an RVI tach to it. Chances are very strong that the tach will not work correctly.

A better choice is to find a Smiths RVC type tachometer as was used on later MGBs and Midgets. As above, RVC will appear on the gauge face. The RVC tachs are a more modern design AND they will work with either points or electronic ignitions. Unlike the figure above, an RVC tach connects to the ignition system using a single wire connected to the coil (-) terminal. Of course, it still needs power, earth, and illumination connections.

Above quoted from another thread,

Your mini will be wired negative earth, early cars were wired positive earth meaning the polarity is different.

Edited by GreaseMonkey, 13 April 2009 - 11:53 AM.

[dklawson]

Er... thanks. Not much I can add to that!

If you stick with older Smiths instruments, look for the above mentioned RVC type. If for some reason you do NOT see RVC on the face, this type can be identified by several features on the back of the tach.
1) It will have two spade lugs on the back, one attached to the case, one on an insulator plate.
2) It will have one (1) bullet connector (NOT 2).
3) Excluding the threaded mounting studs, the RVC tach will NOT (not, not, not) have any other threaded studs on the back.

Almost any modern aftermarket tach will work and be reliable. Don't buy one that goes to 10k RPM, 7k or 8k tachs are all you need for a street car.

[BiMU]

Er... thanks. Not much I can add to that!

If you stick with older Smiths instruments, look for the above mentioned RVC type. If for some reason you do NOT see RVC on the face, this type can be identified by several features on the back of the tach.
1) It will have two spade lugs on the back, one attached to the case, one on an insulator plate.
2) It will have one (1) bullet connector (NOT 2).
3) Excluding the threaded mounting studs, the RVC tach will NOT (not, not, not) have any other threaded studs on the back.

Almost any modern aftermarket tach will work and be reliable. Don't buy one that goes to 10k RPM, 7k or 8k tachs are all you need for a street car.

Ah so would this one work on electronic ignition?

[dklawson]

There are always exceptions... but I'd say "no".

You are showing an RVI tachometer. You should find the letters "RVI" on the bottom of the face. The other tell-tale bit is the threaded brass post sticking out of the back on the right side. That post is for the clamp that holds the inductive loop to the tachometer.

As mentioned in the quoted text above and several other threads on this board, RVI tachometers generally do not work properly with electronic ignitions. Like I said... there are always exceptions, but I wouldn't count on this working with anything but points.

[BiMU]

There are always exceptions... but I'd say "no".

You are showing an RVI tachometer. You should find the letters "RVI" on the bottom of the face. The other tell-tale bit is the threaded brass post sticking out of the back on the right side. That post is for the clamp that holds the inductive loop to the tachometer.

As mentioned in the quoted text above and several other threads on this board, RVI tachometers generally do not work properly with electronic ignitions. Like I said... there are always exceptions, but I wouldn't count on this working with anything but points.

Thanks, it was on eBay and wanted to make sure!