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I've read several places about taking the guts from a later model Sprite tach and swapping the face from a BE tach. The BE tach sweep goes to 6K and the later models go higher. Wont that result in inaccurate reading on the dial? What am I missing or not thinking correctly with the different face sweeps?
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BE Tach Conversion
- Thread starter erstearns
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Trevor Jessie
Yoda
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I dunno, but there are other aftermarket tachs out there with a similar sweep and 6000 rpm range.
dklawson
Yoda
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As Trevor said, the movement doesn't have to be from Smiths, it's just easier that way since they may have the same "depth" from face to the back of the gauge case.
There are versions of both the Smiths RVI and RVC type tachometers that have calibration potentiometers on their circuit boards. By drilling an appropriately located hole in the back of the BE gauge case you will have access to that screw and that in turn will allow you to change the calibration of the donor movement to the BE tach face. However, some of the late RVC tachs do not have any provisions for calibration so they are not good candidates for transplant.
There are versions of both the Smiths RVI and RVC type tachometers that have calibration potentiometers on their circuit boards. By drilling an appropriately located hole in the back of the BE gauge case you will have access to that screw and that in turn will allow you to change the calibration of the donor movement to the BE tach face. However, some of the late RVC tachs do not have any provisions for calibration so they are not good candidates for transplant.
The_architect
Jedi Trainee
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I had the Bugeye tach face put on a RVI gauge by one of the gauge shops frequently referred to here. Other people have done this themselves, I did not trust my skill.
On this RVI gauge the wire goes from the distributor through the firewall to the dash, loops around the back of the gauge and back again to the coil.
I wish I had not bought that kind because if the wire breaks anywhere the car will stop dead. However, I was positive ground at the time and the RVC gauges do not work with positive ground.
RVI gauges come in both positive and negative ground. Make sure you get the right kind, although the positive ground gauges can be converted to negative ground.
I carry an extra short wire I can stick between the coil and distributor should the wire looping through the tachometer break, which is most likely to happen at the terminals. It is not a bad idea to have such a wire made up and carry it in your car even if you do not have this type of gauge.
I believe the RVC gauge has a terminal for positive power, a ground terminal, and a single wire that goes to the coil. No loop.
Steve Maas (Sarastro) has an excellent writeup on this topic on his website. It explains calibration and a lot of other things. He'll be along shortly, I'm sure.
Best of luck
Charlie
On this RVI gauge the wire goes from the distributor through the firewall to the dash, loops around the back of the gauge and back again to the coil.
I wish I had not bought that kind because if the wire breaks anywhere the car will stop dead. However, I was positive ground at the time and the RVC gauges do not work with positive ground.
RVI gauges come in both positive and negative ground. Make sure you get the right kind, although the positive ground gauges can be converted to negative ground.
I carry an extra short wire I can stick between the coil and distributor should the wire looping through the tachometer break, which is most likely to happen at the terminals. It is not a bad idea to have such a wire made up and carry it in your car even if you do not have this type of gauge.
I believe the RVC gauge has a terminal for positive power, a ground terminal, and a single wire that goes to the coil. No loop.
Steve Maas (Sarastro) has an excellent writeup on this topic on his website. It explains calibration and a lot of other things. He'll be along shortly, I'm sure.
Best of luck
Charlie
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Here's the link to my write-up:
https://www.nonlintec.com/sprite/Sprite_Electronic_Tach.pdf
I know that a couple people, at least, have duplicated this.
https://www.nonlintec.com/sprite/Sprite_Electronic_Tach.pdf
I know that a couple people, at least, have duplicated this.
The_architect
Jedi Trainee
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I realized I never answered the calibration question. When the gauge shop put the face on the gauge for me they also calibrated it. That's probably the easiest way to get around this problem.
If you want to do it yourself the link Steve Maas included in his post has a diagram of a circuit that shows how to take power from your wall outlet and drop it to 4 volts AC using a transformer. You can use a similar circuit to SAFELY give yourself a signal source of 12V 60 hertz power to calibrate an RVI gauge as well. You run the 60 hz signal through the loop on the back of the gauge and use the potentiometer set the gauge to read 1800 rpm. This will involve taking the back off the gauge, and you need a separate source of 12 volts DC to power the gauge.
I tried this on the bench and it works, but if what I am talking about does not make sense and you are not used to working with electricity, send it out. Working around 120V is not for everybody.
By the way, if anyone does buy an RVI gauge, be sure that the extra parts that the wire loops through on the back of the gauge are included. I frequently see these gauges on eBay without these extra bits.
They are just a nylon block that holds the wiring, a metal strap, and a tiny round nut that screws onto a post on the back of the gauge. You could rig something up for the nylon block. The little tiny nut that holds this to the back of the gauge is the problem. It must be a weird thread or something, because I could not find anything to fit it.
Charlie
If you want to do it yourself the link Steve Maas included in his post has a diagram of a circuit that shows how to take power from your wall outlet and drop it to 4 volts AC using a transformer. You can use a similar circuit to SAFELY give yourself a signal source of 12V 60 hertz power to calibrate an RVI gauge as well. You run the 60 hz signal through the loop on the back of the gauge and use the potentiometer set the gauge to read 1800 rpm. This will involve taking the back off the gauge, and you need a separate source of 12 volts DC to power the gauge.
I tried this on the bench and it works, but if what I am talking about does not make sense and you are not used to working with electricity, send it out. Working around 120V is not for everybody.
By the way, if anyone does buy an RVI gauge, be sure that the extra parts that the wire loops through on the back of the gauge are included. I frequently see these gauges on eBay without these extra bits.
They are just a nylon block that holds the wiring, a metal strap, and a tiny round nut that screws onto a post on the back of the gauge. You could rig something up for the nylon block. The little tiny nut that holds this to the back of the gauge is the problem. It must be a weird thread or something, because I could not find anything to fit it.
Charlie
The_architect
Jedi Trainee
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Eric, I forgot to mention I bought my RVI tach from The Gauge Shop in the UK. Great service, lots of good looking gauges, and they were able to give me technical support.
You can buy old Smiths tachs off of eBay, but apparently the capacitors in these original gauges sometimes give out and need to be replaced. They had already done this. The gauge looked brand new--they might even swap the face with your Bugeye's and calibrate it too.
Charlie
You can buy old Smiths tachs off of eBay, but apparently the capacitors in these original gauges sometimes give out and need to be replaced. They had already done this. The gauge looked brand new--they might even swap the face with your Bugeye's and calibrate it too.
Charlie