Feeling stupid -- converting tachs

[drooartz]

Okay, I've been reading the documents by our very own Sarastro and Doug Lawson on a couple of ways to convert your mechanical tach to electronic operation, and I'm feeling a bit overwhelmed. I'm not an engineer, though I've done some soldering (mostly guitar repair work). I'm trying to figure out the simplest way to get to a reliable tach operation, while retaining the original Bugeye tach face.

Here's what I have in hand:

* Smiths RVI 2401/01 tach (4"), that I now know is missing the little piece that the wire loops around. Positive ground.

* Smiths RVC 1401/01 AF tach (3"). Unknown if it works, but it looks to be all there. Negative ground.

* Original Bugeye mechanical tach, in working order (though the drive gear box is broken, hence this work to replace the tach).

* Original Bugeye mechanical tach being bid on in eBay. Needs restoration, but the gauge face looks to be in decent shape (that's what I want it for, as I don't want to cut up my original unit).

It would seem to me that I can use the donor Bugeye face, RVC guts, and one of the two 4" cases I'll have to make this all work. I'm just not feeling very confident. Building a circuit board as Sarastro did seems a bit beyond me, or am I just being a wimp? I do own a soldering iron, and have used it to some success in the past.

 

[Sarastro]

In all candor, I wouldn't recommend trying to repeat my project as a first electronics project. Not that it's so difficult, in terms of the electronics, but there are so many pitfalls with getting everything to fit, and so on. For example--one of the biggest problems I had was that the pin from the sacrificed tach was smaller than the original mechanical one, so the pointer needle didn't fit. So, I had to make a plastic insert, drill it out 0.020" diameter, and press the pointer onto the pin. At that point I discovered that it stuck out too far, so the glass face cover wouldn't go on. More mods, finally getting enough clearance.

In fact, I think the hardest part was figuring out how to make it all fit together, mechanically, deciding what pieces to use, making sure there was enough clearance, and all of that.

But, if you're good at dealing with this kind of thing, thinking it out and anticipating problems, it might be fun to do. Might be good also if you know someone electronically knowledgeable who can help with parts and such, and help troubleshoot if it doesn't work.

 

[DrEntropy]

...and I s'pose some watchmaker's training wouldn't hurt either, huh? /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

 

[drooartz]

There's certainly some training involved that my music degree didn't cover! /bcforum/images/%%GRAEMLIN_URL%%/grin.gif

 

[DrEntropy]

Well, you're certainly getting plenty of "OJT" with the Tunebug! /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[drooartz]

You ain't kidding, Doc.

I haven't felt this ignorant since I was a little kid! At least I'm not (normally) afraid to push past that and get on with the learning. Part of why I enjoy it, really.

 

[DrEntropy]

"Ignorant"?!?! BAH!! You've got books, the actual MACHINE and the BCF as source reference!!!

"Ain't nuttin' ya can't do" with a bit of concentration.


...don't hurt to have a few "spares" lyin' about, either. /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

 

[drooartz]

I count on all of those things, Doc. Doing it still seems to be the only way to gain real understanding, though.

 

[spritenut]

Drew

Here's what you do.....
Use the 3" Neg ground tach guts. Stick them in the 4" tach housing, some dremel or filing will need to be done to the housing. Now just screw the Bugeye face to the guts of the 3" tach and use the needle. All are interchangable unless you have the late 3" tach with the dial plate screws going verticle. (73 on tach) You can do the same with the 65-67 4" tach, just swap guts, dial, and needle. Now all the gauges match. I don't know why ther Bugeyes/MKIIs had a silver face but the smaller gauges are black and so are the 65 on dials.
So "matching" is not the word, it's a combo of silver and black face gauges.

 

[drooartz]

Thanks, Frank. Sounds like I've got a plan in there somewhere. The 3" tach is the vertical one (74 Midget tach), however, so the proper one may need to be sourced.

 

[spritenut]

Drew
You can use the 74 tach guts, I did just that on my 59.
I drilled the holes to match the horizonal screws.
You have to look real close to see the verticle holes.
I'm sure a spot of black dum-dum from the back side would hide the holes.
That 74 tach is a negative wire hook up. No white wire loop.
I forget the wire color but all you need is a wire from the bullet connector to the - side of the coil.
The spade terminal gets a green wire (hot with key on) and a close jumping point is the gas gauge where the green wire (b terminal) hooks to. Some even have a spare terminal already.

 

[drooartz]

Thanks, Frank, that's comforting to hear. I'll have to play a bit and see what I can do with the bits I have on hand.

I assume to use the 74 tach I'll need to convert the Tunebug to negative ground. No big issue there, just clarifying.