Mechanical tach options?

[tdskip]

Hi guys - I have a Petronix in my Bugeye with a later Sprite tach. Check me on this - but I believe the early tachs were mechanically driven which would be preferable to electronic since the Petronix units typically don't play nice with the electronic tachs.

Any coaching or tips to pass along?

 

[Trevor Jessie]

Pertronix works fine with most tachs. Yes early tachs were driven from the generator (not the distributor)

 

[dklawson]

Smiths RVI (early electric) tachs do not work well with Pertronix and other electronic ignitions. The later RVC type Smiths tachs (as well as almost any aftermarket tach you can find) work fine with electronic ignitions.

 

[tdskip]

How do you tell if you have the later Smith tach?

 

[dklawson]

Don't focus on "early vs late" in the text that follows. Focus on RVI vs RVC.

To identify your tach, start by looking at its face. Typically you will find the type printed in white (RVI or RVC).

If you don't find RVI or RVC on the face, turn the tach over and look at the back of the case. If you see an insulating plate with two bullet connectors (one male, one female) that is a late RVI type tach. If you don't see any bullet connectors but you see a screw terminal (which may or may not have a "C" shaped piece of metal and a thumb nut... maybe with a loop of white wire in it), that is an early RVI type. (Paraphrasing... RVI types either have 2 bullet connectors or NO bullet connectors).

RVC types are simpler on the back. They will have a single male bullet connector AND a male spade lug both on an insulated plate. The case may have a male spade lug spot welded in place. If there is no spot welded male spade, the gauge gets its ground connection through the threaded studs used with the mounting brackets.

For electronic ignitions you want the RVC type.

My links never work so cut and paste the addresses below as needed:
Early RVI: https://www.lotus-cortina.com/electric/tach2b.jpg
Late RVI: https://i12.photobucket.com/albums/a233/tegwin/cropped.jpg

RVC type: https://www.locostbuilders.co.uk/gallery/a250554-Rev%20Rear%202.JPG

 

[tdskip]

 

[tdskip]

My gauge face, of course, isn't marked

 

[dklawson]

Sorry it's not marked. Can you identify a match to one of the three picture links? If not, can you post a picture of the back of your tach?

 

[60bug]

I have an RVC tach but which connections go where? Mine has the male spade connector and the round bullet connector, very similar to the one with the 511 sticker.

 

[tdskip]

Sorry it's not marked. Can you identify a match to one of the three picture links? If not, can you post a picture of the back of your tach?

But Doug, I did my weeks worth of hanging upside down dropping dust into my eyes last night.... Grin.

 

[Sarastro]

Look around a bit--there are places that will replace the innards of your mechanical tach with modern electronics. I'm not at home right now, so I can't dig out the names of the places, but a little googling should do it.

 

[dklawson]

I have an RVC tach but which connections go where? Mine has the male spade connector and the round bullet connector, very similar to the one with the 511 sticker.

Look again carefully. The one with the 511 sticker is an RVI tach. It has 2 bullet connectors next to the male spade lug. If your tach is an RVC and has one male spade and one round bullet it will look more like the bottom picture. Don't focus on the lamps on the back, just the electrical connectors.

The RVC wiring is very simple. The case gets a ground connection. The male spade lug next to the bullet connector gets switched, fused 12V power. The bullet connector is connected to coil (-) (the distributor side of the coil).

 

[tdskip]

Well I've got an RVI tach in her now (at some point will switch back to a correct Bugeye gauge).

 

[60bug]

Thanks Doug, looks like I have the RVC type which will work with my Pertronix ignition, I was concerned it wouldnt work with the pertronix.

 

[tdskip]

So I should be able to find a cheap RVC and connect it up, yes?

 

[dklawson]

eBay is your friend. There are lots of RVC tachs out there but most will look out of place in the dash of an early car. For starters, many were made with 80mm diameter housings instead of the larger 100mm size of early cars. Smiths also altered the font style over the years and the later gauges had a decidedly more "modern" appearance.

You can search for "RVC tachometer" but that won't lead to a lot of matches. You can use general searches like "Smiths tachometer", "MG tachometer", "Midget tachometer" and then look carefully at the pictures to make sure its an RVC. If you are not worried about the modern look, add "Spitfire tachometer" to your search.

 

[60bug]

I had to retrofit the innards from a later RVC tach to the 100mm canister from the RVI tach, it was a perfect fit.

 

[tdskip]

eBay is your friend. There are lots of RVC tachs out there but most will look out of place in the dash of an early car. For starters, many were made with 80mm diameter housings instead of the larger 100mm size of early cars. Smiths also altered the font style over the years and the later gauges had a decidedly more "modern" appearance.

Yeah, agree on the look. I have a "custom" dash now with later gauges anyway so not a big deal at this point.

I'll see if I can scare one up.

Thanks guys!