Bugeye tach conversion question

[Jimflorida]

I have been reading posts on this for over an hour, and am not much smarter than when I started (and may have actually lost a brain cell or two). Like many others, I have converted my Bugeye to an alternator and to negative ground. I need to replace my mechanical tach with an electronic version, and plan on taking the faceplate off my original tach and putting it on a later tach, as a number of people have suggested. What is not clear to me is which later tachs are usable for this conversion. From what I understand, the 65-67 sprite/midgets have the 4" RVI tach that I would need, but are positive ground, although others have provided instructions to convert those to negative ground. I think there were also later tachs that were 4" and negative ground, but am not sure. Also, the later RVC tachs are usable, I believe, but am not sure which of these may be usable. Can anyone give me a cheat-sheet on which tachs are usable? Thanks,
Jim

 

[David_Doan]

Jim,

I just did this with an RCV tach from a later model spridget. RVC is electrically easy because it is negative ground, but it is smaller in diameter so the mechanical swapping of the guts is a lot more work. If i did it again, I would start with a spitfire tach. They are RVC, negative ground and the same size as the original tach.

Here's a link to one i found on ebay:

https://www.ebay.com/itm/120891420737?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I have not done this, but I have read that it will work. It would also need re-calibration since it is set up to go to 7000 rpm, vs. 6000 on your current tach.

Note: The reason I leaned towards an RVC is that they are also compatible with electronic ignition. Converting an RVI to negative ground is probably the easiest to do at the end of the day.

 

[Rut]

Jim,
i did the RVC conversion as well and the donor tach was a 4" unit. Very easy to swap the face plate, but the pin the needle fits on is smaller on the RVC...at least it was on my Bugeye tach. I chose the RVC for the same reasons David did and I changed a few more things. I painted the inside of the case white and added a self adhesive LED strip to improve the lighting and I have an LED dimmer to adjust the brightness. I found my tach on eBay for $20 or so and searched until I found an RVC in 4". The RVC tach also has a screw on the rear to adjust and/or calibrate it.
HTH, Rut

this is the tach I used
https://www.ebay.com/itm/1971-1980-...pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

 

[dklawson]

I have not converted a Bugeye tach but have done others. I would like to add general footnotes to what has been said above.

The RVC tach is a better choice (in most cases) not because of polarity but because of age and the simplicity involved in connecting/wiring it. The RVC tach will be "newer" than an RVI and most are indeed negative ground. However, of more significance to me, the RVC is easier to connect requiring only power, earth, and a single sense wire to coil (-). The RVI tach is more complicated to install because it is wired "in series" with current flowing through the ignition coil. It is NOT hooked to the coil with a single wire. Finally, the RVC tach is compatible with electronic ignitions while the RVI generally is not.

There is one caveat. The very late RVC tachs often had NO calibration pot on their circuit board. Sorry, I cannot tell you which tachs do and which do not. Therefore, if you can... select an RVC tach whose face/needle have the same degree of needle sweep as your original Bugeye gauge.

 

[bugedd]

When I do mine, I'm sending it to Palo Alto Speedometer. They will convert your stock tach to electric for $295. Pricey, but it will be done right.

 

[Jimflorida]

Thanks. I'll look for the RVC tach for the conversion. I had thought about having Palo Alto Speedometer do it too, but it is costly--maybe that will be my back-up plan.
Jim

 

[dklawson]

$295 may seem pricey but it really isn't when you consider the labor involved. With the exception of a few repeat/duplicate conversions, each gauge is unique. There are often custom pieces like spacers that have to be machined, some hand fitting of parts, and of course... calibration. There will typically be cosmetic repairs also. When you consider what you pay a mechanic at a dealership to fix your modern car, paying a professional shop to convert your gauge doesn't seem bad at all.

That said, I consider each such project a unique and new challenge that I enjoy. However, I fully understand that not everyone wants to undertake things like gauge conversion projects.